Friday, November 30, 2007

Nursery - Overwintering Container Grown Ornamentals

One important part of successful production of container grown ornamentals is overwintering. The following is an article on the subject.

How can container grown plants be stored for winter? Plants produced in containers may require winter protection to protect them from desiccation and root damage from freezing. Many plants grown in zone 7 will require some type of protection from freezing temperatures, although plants with very low root killing temperatures will survive with minimum protection. The type of overwintering technique used (structureless or structure) is determined by the plant species and the ability of their roots to withstand cold temperatures during winter.

Growers must first determine the extent of winter protection required for the plants he grows. Plants whose roots are killed at higher temperatures than the average low temperature in their area will need some type of protection. Plants with roots that can withstand colder temperatures may only need to be consolidated and the outside perimeter protected with bales of hay or bags of leaves. This can save valuable time and money compared to using more significant systems.

Following are several overwintering systems for container grown plants:

Polyhouse - This is the most common type of overwintering structure and allows the most protection to plants. A Quonset type structure is the most common and is generally 14’ wide, 7’ high in the middle, and approximately 100’ long. Construction is simple and fairly inexpensive. They are built from 3/4" galvanized water pipe or 1" heavy walled electrical conduit which is bent into a half circle (or 2 quarter circles can be connected easily when using electrical conduit) and placed at 4’ to 5’ intervals. Securing the bent pipe over steel rods hammered into the ground supports these. The ends are enclosed by plywood with vent doors placed at each end. Exact construction details can be obtained through the Cooperative Extension Office.

Polyhuts - These are similar to polyhouses but are low, copolymer-covered structures used mostly for herbaceous perennials, ground covers, and low growing woody ornamentals. The structure is 5 - 6’ wide, 4’ high, and any length. Construction is similar to the polyhouse.
Both of these structures are covered with 4 - 6 ml white polyethylene for the best protection. White polyethylene is preferred over clear poly since it reflects solar radiation and will not heat up as much at mid-day as clear polyethylene thus reducing temperature fluctuations and heat build up.

The temperature inside polyhuts has been shown to stay warmer and maintain higher relative humidity than polyhouses but the variation in temperature is greater and may be undesirable. This also means temperatures inside polyhuts will increase faster in late winter due to decreased buffering capacity. Also, it is harder to monitor and work on plants during the winter in ployhuts compared to polyhouses.

House orientation has been shown to influence the temperature inside the house. Houses oriented in a north-south direction are cooler at mid-day than houses in a east-west orientation. Houses in an east-west direction therefore have larger temperature fluctuations over the course of the day. Reducing these temperature fluctuations is important to reduce cold damage and desiccation injury. It is not uncommon for temperatures in a house covered with clear poly and oriented in a east-west fashion to approach 70°F and the leaf temperature to approach 100°F on a clear winter day with temperatures of 30°F. In this situation transpiration and plant desiccation can occur especially if the relative humidity is low and the media is frozen. It is important to maintain a high relative humidity to reduce transpiration. By using white poly and orienting overwintering structures north-south, cooler leaf and air temperatures inside the house are obtained thus reducing transpiration.

These two systems work satisfactorily for most plants. When growing plants which can sustain root injury at relatively high temperatures, additional protection may be necessary. This protection can include covering the plants with microfoam or a layer of clear poly. Microfoam is a flexible, high efficiency, lightweight insulation sheeting which is very effective. Another option for protecting root sensitive species grown in areas where winter temperatures are low is the concept of ‘minimum heat’. In this system some type of heat is employed to keep the soil temperature at a minimum of 25°F. It is important to note that the temperature sensor should be placed in the media to determine media temperature rather than air temperature in the house.

The temperature around the inside perimeter of the house will be colder than the middle of the house. When the plants are placed pot to pot, the pots on the outside edge are only protected on 3 sides. These plants will be colder in the winter and will warm up first in the spring. If possible, place cold sensitive species in the center of the house and more tolerant species around the edge. Another approach would be to place bags of leaves or bales of hay around the outside edge of the house or place styrofoam sheets around the inside.

Structureless systems - Another method of overwintering plants is by laying protective covers directly over plants and securing the edges. These systems provide more insulating protection to the plants than structure-supported systems but are not used as commonly for several reasons. The big disadvantage of this system is you can not check the plants as easily. Once the plants are covered, they should remain sealed for the winter. Also, towards the end of the winter when day temperatures increase, venting to inhibit plant growth is more difficult. When using these systems larger plants are laid on their sides with the crowns towards the middle.
Poly-straw-poly - An older but less common method is to consolidate the plants and cover them first with a layer of clear poly, then 6" - 12" of straw, and then a layer of white poly. They straw acts like an insulation barrier, protecting the plants. A main disadvantage of this system is the straw becomes wet from condensation and clean up can be messy.

Microfoam-poly cover - A more effective and cleaner method is to consolidate the plants and cover with microfoam. White poly is laid over the microfoam and secured around the perimeter.
No covering - Some plants are root hardy enough that no protection may be necessary unless very unusual winter temperatures are experienced. Plants such as Juniperus horizontalis "Wiltoni", J. h. "Plumosa", Picea glauca, Picea omorika, and Potentilla fruticosa have low root killing temperatures. These plants may only need to be consolidated and left uncovered. If the area is not protected from winter winds, then it may be advantageous to protect the perimeter with bales of hay or bags of leaves. If this system has not been a regular practice at your nursery, it is advisable to try this with a few plants of each species. The advantage of this system is valuable overwintering space is freed up and your production area is increased.

Caring for overwintering plants:

Covering the plants for winter - Plants should be completely dormant or hardened off before covering for the winter. Plants begin the dormancy process by responding to the increasing length of darkness. The second stage of acclimation is caused by exposure to cold temperatures such as autumn frosts. Plants should not be covered before they have acclimated to cold temperatures. This is sometime in November or early December. Cover plants that are prone to stem splitting from early frosts, such as evergreen azaleas, earlier as long as there is ample ventilation during sunny days.

Watering - Before covering, consolidate plants as close as possible and water well. Moist media freezes slower and releases heat compared to dry media offering protection to the roots. The moisture the relative humidity, which helps guard against desiccation. Structureless systems will not need watering if sealed properly.

Uncovering - After the plant’s chilling requirement has been satisfied, plants can respond to warm temperatures. In late winter as the temperature increases, plants can deacclimate to cold temperatures. If the temperature decreases slowly, plants can reacclimate to colder temperatures but fast drops in temperature can cause cold injury to plant tissue. Although white polyethylene covered houses warm up less, vent the house by opening the end doors if the inside temperature approaches 45-50°F. Plants should not be uncovered until after the danger of subfreezing temperatures. In early spring, some nurserymen cut holes in the poly to ensure adequate ventilation while still providing adequate protection from frosts. Although difficult, it is important to check that growth of plants under structureless systems hasn’t started. Depending on the materials used to protect plants they can have a high insulating value that is effective at retaining heat. Etiolated growth can occur and be very susceptible to cold injury. By uncovering, the plants will remain dormant. This can be a nuisance where mild temperatures occur periodically during the winter.

In summary, proper overwintering of container grown ornamentals is essential to maintain high plant quality. Several overwintering systems have been developed. The choice depends on capital as well as the amount of protection required by the plants. Economically, it doesn’t make sense to over-provide winter protection. To overwinter plants, group the plants together, water thoroughly, and cover the plants after they have acclimated to the cold but before danger of subfreezing temperatures. Adequate moisture should be maintained and irrigation may be necessary during the winter when using some overwintering systems. Uncover the plants when temperatures begin to increase in early spring but after danger of subfreezing temperatures.

Modified from "Overwintering Container Grown Ornamentals" by the University of Massachusetts Cooperative Extension.

Greenhouse and Nursery - Monitor your Meters

Meters used to monitor pH and salts in greenhouse and nursery media, directly, in saturate paste extracts, or in the leachates in the pour throught methods, are extremely useful management tools. However, they must be regularly calibrated, maintained properly, and electrodes need to be replaced when not performing properly. The following is a short article on the subject.

We often tell you to monitor the pH and soluble salt levels of your substrates, but growers sometimes forget to check their meters. Regardless of the quality of your equipment, the probes on these meters do have a shelf-life. You may need to replace the probe on your meter about every two years. The probes can be replaced by contacting the supplier where the meter was purchased. You should from time to time send a sample to a commercial lab for testing for comparison of pH. A unit may be off even though you are regularly calibrating your meter with fresh buffer solution (remember that these also have a shelf-life). It’s a good idea to compare your results with a commercial lab once a year. To extend the life of the soil probes make sure to keep the probe tip in buffer solution and do not allow the tip to dry out.

Modified from and article in the February 2, 2007 issue of the Greenhouse TPM/IPM Weekly Report from the University of Maryland Cooperative Extension

Thursday, November 29, 2007

Landscape and Nursery - Deer Activity

Deer damage can be more severe starting this time of year. The following is a short article on the subject.

Be cautious when driving because deer are all over the roadways in the evening and morning hours. Four things are causing lots of deer movement at this time of year: 1) Cold weather tends to encourage deer to migrate around an area. They hunker down in cold, wet weather. 2) It is bow season and this makes deer jumpy. 3) Farmers have cut most of the corn fields and soybean fields at this point and the deer will migrate from the fields toward wooded areas. 4) Finally, it is still mating season so deer tend to migrate around looking for each other.

Monitor and protect your young pansy plants since deer love to browse on them if they are out in the open. A local facilities manager in charge of deer spraying called this week and said that he had noticed that the deer were particular about which plants they ate in an unsprayed pansy staging area. He noted that when they planted “majestic giant” pansies that the deer did not attack the beds as much.

Also expect more deer damage in general in landscapes now that that crops are harvested. Take measures to protect sensitive plants. Repellant techniques such as soap hung on trees and shrub and human hair can be used on a small scale. Some areas may require electric livestock fencing to help keep deer away (contact your extension office on how to "train" deer to avoid these electric fences). In nurseries, a tall deer exclusion fence may be necessary to protect valuable plants.

Adapted and modified from an article in the November 16, 2007 edition of the Greenhouse TPM/IPM Weekly Report from the University of Maryland Cooperative Extension

Landscape - Proper Planting

Proper planting is critical in establishing trees and shrubs. The following are some guidelines to follow in planting landscape plants.

Plant and Site Selection

Select trees and shrubs well-adapted to conditions of individual planting sites. Poorly-sited plants are doomed from the start, no matter how carefully they’re planted.

Test soil drainage before planting. Dig a test hole as deep as your planting hole and fill with water. If water drains at a rate of less than one inch per hour, consider installing drainage to carry water away from the planting hole base, or moving or raising the planting site (berm construction).

Also consider using more water-tolerant species. For trees, try red maple, sycamore, bald cypress, willow oak, or river birch. For shrubs, try inkberry, redtwig dogwood and buttonbush. Avoid dogwoods, azaleas, boxwoods, Japanese hollies, and other plants that don’t like “wet feet” where drainage is poor.

Examine soil for compaction before planting. If soils are compacted, consider replacement with a good loam soil, or incorporation of several inches of an organic material such as composted yard waste to a depth of at least 8 inches over the entire planting area. Do not incorporate small quantities of sand - compaction will increase and drainage decrease.

Site Preparation

Dig shallow planting holes two to three times as wide as the root ball. Wide, shallow holes encourage horizontal root growth that trees and shrubs naturally produce.

In well-drained soil, dig holes as deep as the root ball. In poorly-drained heavy clay soil, dig holes one to two inches shallower than the root ball. Cover the exposed root ball top with mulch.
Don’t dig holes deeper than root balls or put loose soil beneath roots because loose soil will compact over time, leaving trees and shrubs planted too deep. Widen holes near the soil surface where most root growth occurs. Score walls of machine-dug (auger, backhoe) holes to prevent glazing.

Backfill holes with existing unamended soil. Do not incorporate organic matter such as peatmoss into backfill for individual planting holes. Differences in soil pore sizes will be created causing problems with water movement and root growth between the root ball, planting hole, and surrounding soil.

Backfill half the soil, then water thoroughly to settle out air pockets. Finish backfilling, then water again. Cover any exposed root ball tops with mulch.

It is generally not recommended to put fertilizers in the planting hole. Howver you can incorporate slow-release fertilizers into backfill soil to provide nitrogen, or if a soil test indicates a need for phosphorus or potassium. Avoid using fast-release agronomic fertilizers that can dehydrate tree roots. Use no more than 1# actual nitrogen per 1,000 ft. of planting hole surface. (Example - if using 18-6-12 with a 5' diameter hole, incorporate 0.3 oz. per planting hole.)

Tree and Shrub Preparation

Closely inspect the wrapping around root balls of B&B (balled and burlapped) trees and shrubs. Growers use many synthetic materials, as well as burlap treated to retard degradation, to wrap root balls. Many of these materials will not degrade. To insure root growth into surrounding soil, remove pinning nails or rope lacing, then cut away or drop the wrapping material to the bottom of the planting hole, backfilling over it.

Wire baskets used to protect root balls degrade very slowly underground. Remove the top 8-12 inches of wire to keep equipment from getting caught in wire loops, and surface roots from girdling.

Remove all rope, whether jute or nylon, from trunks. Again, degradation is slow or nonexistent, and ropes can girdle trunks and roots.

Remove plastic containers from container-grown trees and shrubs. For plants in fiber pots, break away the top or remove the pot entirely. Many fiber pots are coated to extend their shelf life, but this slows degradation below ground and retards root extension.

In container palnts, if roots are circling around the root ball exterior, tease the roots out with a hand fork to prevent circling roots from eventually girdling the trunk. Cut any that stay circling. Select trees grown in containers with vertical ribs or a copper treatment on the interior container wall. These container modifications and treatments minimize circling root formation. Remove as much of the media as possible from the root ball without damaging the roots. This will allow the plant to root mor quickly into the soil.

Tree Care After Planting

Remove tags and labels from trees and shrubs to prevent girdling branches and trunks. Good follow-up watering helps promote root growth. Drip irrigation systems and water reservoir devices can facilitate watering.

Mulch, but don’t over mulch newly planted trees and shrubs. Two to three inches of mulch is best - less if a fine material, more if coarse. Use either organic mulches (shredded or chunk pine bark, pine straw, composts) or inorganic mulches (volcanic and river rocks).

Keep mulch from touching tree trunks and shrub stems. This prevents disease and rodent problems if using organic mulches, and bark abrasion if using inorganic mulches.

Don’t use black plastic beneath mulch around trees and shrubs because it blocks air and water exchange. For added weed control, use landscape fabrics that resist weed root penetration. Apply only one to two inches of mulch atop fabrics to prevent weeds from growing in the mulch.

Only stake trees with large crowns, or those situated on windy sites or where people may push them over. Stake for a maximum of one year. Allow trees a slight amount of flex rather than holding them rigidly in place. Use guying or attaching material that won’t damage the bark. To prevent trunk girdling, remove all guying material after one year.

Most trees should not have their trunks wrapped. Wrapping often increases insect, disease, and water damage to trunks. Thin-barked trees planted in spring or summer into hot or paved areas may benefit from wrapping if a white wrap is used. To avoid trunk girdling, do not attach wraps with wire, nylon rope, plastic ties, or electrical tape. If wraps must be used, remove within one year.

For protection against animal or equipment damage, install guards to protect the trunk. Be sure the guards are loose-fitting and permit air circulation.

Adapted from the fact sheet "Tree and Shrub Planting Guidelines" Authors: Bonnie Lee Appleton, Extension Specialist and Susan French, Extension Technician,AREC, Hampton Roads; Virginia Tech

Wednesday, November 28, 2007

Turf - Understanding Moles

Moles and mole damage is often not well understood by turf managers. The following is a short article on these pests.

Moles belong to the group of mammals that are insect eaters. They are often incorrectly called "rodents," the group or family of animals such as mice, rats, and squirrels. There are different species of moles in the United States. However, the common mole is the most widespread in the East and is the most likely mole encountered in Delaware.

Description and Habits

Moles have short, velvet-like fur that varies in color from gray to brown. A fully grown mole is 4 to 6 1/2 inches long, not including its short tail. Adults weigh 3 to 5 ounces. The eastern mole has a long naked snout with nostrils that open upward. Moles have a voracious appetite and can eat 70-100 percent of their weight daily. They feed while burrowing just below the surface of the ground where their preferred foods, including insect grubs, adult insects, and earthworms, are abundant. Plant parts are eaten only occasionally.

Moles live alone, but burrow systems of several moles may connect. Burrowing occurs year-round, peaking during warm wet months. When making feeding tunnels near the surface, moles may burrow up to one foot per minute. A single mole can create an extensive network of burrows. Moles tend to burrow along structures, fence lines and walkways. Therefore, one animal can be responsible for considerable damage to a lawn or garden.

Breeding takes place in February and March; young are born 42 days later. Females produce one litter of four or five young per year. Young are independent of their mother at one month and reach sexual maturity in one year.

Moles live underground and seldom venture out of their burrows. They are most active early in the morning and late in the evening. The ridges produced by their burrowing plainly indicate their presence. Most of the tunneling is done in a random search for food, so many of the tunnels are seldom re-used. This is important to remember when trapping moles. Their more permanent or "active" tunnels usually run along fences, borders or other protected places that lead to feeding areas.

Moles feed almost exclusively on soil insects -- earthworms and grubs are the most important food sources. Because they eat insect pests, they can be beneficial. A mole has a tremendous appetite and can consume nearly half its own weight in food daily. Roots, bulbs and tubers of plants are not target food sources, but may be damaged indirectly as moles dig through the ground in search of grubs and earthworms. Plant parts may subsequently be eaten by mice, which use mole tunnels for protection and as avenues to food supplies.

Information from the UD Extension Fact Sheet HYG-61 and the University of Nebraska Extension Factsheet on "Moles and Their Control"

Landscape - Rust Mites on Conifers

Landscapers may have seen some damage by rust mites on conifers this fall. They also can be problems in early spring. The following is an article on these pests and when to have them on the calendar to look for.

CONIFEROUS RUST MITES. Rust mites are tiny microscopic creatures that cause a silvering or bronzing to the plant needles they affect. Two species present in spring and fall are the hemlock rust mite (HRM) and the white pine sheath mite (WPSM). Hemlock rust mite mostly feeds on hemlock and occasionally on spruce. It feeds on the margins and upper surface of needles, turning them an olive-green to silver-green color. Premature needle drop can occur in heavy infestations. HRM can be found any time of year, but has population peaks in the early spring (around 265-471 GDD) and again in late October to Early November. Bloom of Cornus mas (Cornelian cherry dogwood) may coincide with the spring HRM peak.

White pine sheath mite feeds on white pine and inhabits the innermost portion of the needle bundle, where it causes spotting/”russetting” of needles. Excessive stunting of old needles may also result from its feeding. Damage from WPSM is often mistaken for air pollution, phytotoxicity, or seasonal needle drop when first observed. WPSM can be found in early spring but late summer-fall populations are also observed. Penn-Del IPM research group data and Longwood research show peaks around 275 GDD and again after 1000-2000 GDD (August to late September). Bloom of Acer saccharum (Sugar maple) may be a plant phenological indicator for WPSM.

Monitoring for rust mites is tricky. A hand lens is usually inadequate. Instead, beat sampling branches over a funnel and into a vial, filling the vial with water or rubbing alcohol afterward. View the vial contents in a dish with a 40x or higher dissecting scope (inexpensive scopes are fine). Rust mite eggs are slightly larger than the mites themselves and are often observed at the base of infected needles. Manage rust mites with sprays of 2% horticultural oil or a labeled product such as Avid (abamectin) or Forbid (spiromesifen). Many of the newer selective miticides have no affect on rust mites, so be sure to check the label prior to treatment. Naturally occurring biological controls such as predatory mites will eat rust mites, so critically evaluate the need for spraying before application.

Article by Casey Sclar, IPM Coordinator, Longwood Gardens in the UD Cooperative Extension Ornamentals Hotline, April 7, 2006.

Tuesday, November 27, 2007

Greenhouse - Edema or Water Blisters

Edema on Ivyleaf Geranium
Photo from Iowa State University Horticulture Home and Pest News.

Edema or water blistering is a common problem in some greenhouse grown plants such as ivyleaf geranium. The following is a short article on the subject.

During periods of cloudy weather, greenhouses are apt to be cool and humid. These environmental conditions favor the development of edema (oedema). When the growing media remains moist and the plant roots absorb water at a faster rate than is transpired through leaf cells, the leaf cells rupture. This rupturing of the leaf epidermis and the inner cells causes the raised, crusty appearance on the underside of the leaf.

Edema is commonly found on ivy geraniums and cultivars vary in their susceptibility. Experienced growers will select varieties less susceptible to the problem. Other greenhouse crops susceptible to edema include: sweet potato vine (ipomea), begonias, cacti, ferns, palms, pansy, cleome and cole crop vegetables like broccoli, cabbage and cauliflower.

Symptoms of edema appear as bumps or blisters initially on the undersides of lower or older leaves on a plant. They may then turn brownish or tan and become corky. Severely affected leaves will turn yellow and fall off the plant.

To reduce the incidence of edema: Use a well drained growing media, avoid over watering, and keep plants on the "dry side" during extended periods of low light and cool temperature. Plants grown in saucerless hangers with reservoirs of water inside the pot are more prone. Ventilate whenever possible to lower humidity and use horizontal air flow (HAF) fans to hasten air movement and maximize plant transpiration. Increase light intensity. Space plants farther apart. Avoid over-fertilizing plants, and avoid cultivars that are highly susceptible to edema in your greenhouse.

Article from the University of Massachusetts Floriculture Timely Topics, 3/2/04.

Recommended Plants For Kent County - Serviceberry

Apple Serviceberry, Amelanchier x grandiflora
Photo from Plants for a Liveable Delaware publication
This is a continuation of the series on recommended plants for Kent County. Apple Serviceberry is a shrub or small tree with early bloom and good fall color. The following is information on this species.

Serviceberry (Amelanchier x grandiflora) – 15-25’ tall with very early white flowers covering the tree, attractive fruit and orange fall color; single stemmed cultivars are available, native plant.

Amelanchier x grandiflora is sometimes called Apple Serviceberry. Apple Serviceberry is a hybrid between Amelanchier canadensis and Amelanchier laevis that grows 15 to 25 feet tall. Multiple stems are upright and highly branched forming a dense shrub, or if properly pruned in the nursery, a small tree. It is superior to either species in that it suckers less and is adapted to a wide range of soils, and tolerates some drought. The main ornamental feature is the white flowers that are larger than those of other Amelanchiers. The flowers are borne in early spring and are at first tinged with pink but later fade to white. The young leaves are purplish and the fall color is yellow to orange. Edible fruit attracts birds. Well adapted for planting beneath power lines due to its small size. There are several disease and insect pests of Serviceberry that may need be be controlled in some cases.
Information taken from Plants for a Liveable Delaware publication and the University of Florida Fact Sheet ST-77 by Edward F. Gilman and Dennis G. Watson.

Monday, November 26, 2007

Landscape - Trees and Shrubs Rarely or Seldom Damaged by Deer

Deer damage can be quite severe in the landscape. As more development occurs in Delaware, deer are becoming adapted to surviving in and around our suburban areas. Landscapers may therefore choose to plant species that are not commonly damaged by deer. The follow is a partial list of trees and shrubs to consider.

Trees and Shrubs Rarely Damaged by Deer.

Aesculus parviflora, Bottlebrush Buckeye
Amelanchier arborea , Downy Serviceberry
Amelanchier canadensis, Shadbush
Amelanchier laevis, Allegheny Serviceberry
Betula albo-sinensis, Chinese Paper Birch
Betula nigra, ‘ Heritage’ Heritage Birch
Betula papyrifera, Paper Birch
Chamaecyparis pisifera, Japanese Falsecypress
Cryptomeria japonica, Japanese Cedar
Ilex x aquipernyi, ‘Dragon Lady’ Dragon Lady Holly
Ilex x aquipernyi, ‘ San Jose’ San Jose Holly
Picea pungens glauca, Colorado Blue Spruce
Arctostaphylos uva-ursi, Bearberry
Asimina triloba, Pawpaw
Berberis spp., Barberry
Buxus spp., Boxwood
Caryopteris x clandonensis, Caryopteris
Calastrus scandens, American Bittersweet
Cornus sericea, Red Osier Dogwood
Cephalotaxus harringtonia var. koreana, Japanese Plum-Yew
Gaultheria procumbens, Creeping Wintergreen
Gaultheria shallon, Shallon
Hibiscus syriacus, Rose of Sharon
Ilex x ‘John T. Morris’, John T. Morris Holly
Ilex x ‘Lydia Morris’, Lydia Morris Hollies
Leucothoe spp., Leucothoe
Pieris japonica, Japanese Andromeda
Rhamnus cathartica, Common Buckthorn
Sambucus canadensis, Blueberry Elder
Sarcoccoca hookeriana var. humilis, Dwarf Sweet Christmas Box

Trees and Shrubs Seldom Damaged by Deer

Betula pendula, European White Birch
Cornus florida, Flowering Dogwood
Cornus kousa, Korean Dogwood
Crataegus laevigata, English Hawthorn
Fagus sylvatica, European Birch
Gleditsia triacanthos, Honey Locust
Ilex opaca, American Holly
Lindera benzoin, Spicebush
Picea abies, Norway Spruce
Picea glauca, White Spruce
Pinus nigra, Austrian Pine
Pinus mugo, Mugo Pine
Pinus resinosa, Red Pine
Pinus rigida, Pitch Pine
Prunus serrulata, Japanese Flowering Cherry
Sassafras albidum, Common Sassafras
Salix matsudana ‘Tortuosa’, Corkscrew Willow
Buddleia spp., Butterfly Bush
Calycanthus occidentalis, California Sweetshrub
Ceanothus spp., Cheonothus
Choisya ternata, Mexican Orange
Cistus spp., Rock Rose
Cornus sanguinea, Bloodtwig Dogwood
Daphne spp., Daphne
Enkianthus campanulatus, Redvein Enkianthus
Forsythia spp., Forsythia
Hippophae rhamnoides, Sea Buckthorn
Ilex glabra, Inkberry
Jasminum nudiflorum, Winter Jasmine
Juniperus chinensis, Chinese Juniper
Kerria japonica, Japanese Kerria
Kolwitzia amabilis, Beauty Bush
Laurus nobilis, Laurel
Lonicera spp., Honeysuckle
Mahonia spp., Grape Holly
Myrica pensylvanica, Bayberry
Nandina spp., Heavenly bamboo
Osmanthus heterophyllus, Holly Osmanthus
Philadelphus spp., Mock Orange
Prunus laurocerasus, Cherry Laurel
Ribes spp., Currant
Spirea spp., Spirea
Syringa villosa, Late Lilac
Syringa vulgaris, Common Lilac
Viburnum juddii, Judd Viburnum
Viburnum rhytidophyllum, Leatherleaf Viburnum
Viburnum carlesii, Koreanspice Viburnum
Viburnum plicatum, Doublefile Viburnum
Weigela florida, Weigela

Information extracted from Maryland Cooperative Extension Fact Sheet 655

Sunday, November 25, 2007

Greenhouse - Prepare for Spring Pansy Production

Greenhouse growers are in the midst of poinsettia sales season now. The next major production plant for many growers will be spring pansies. The following is information on pansy problems to avoid.

Growers will be once again starting their spring pansies in December. Just a few reminders on what to watch out for on your pansy crop:

Root rots- look for stunting, wilting, and yellowing. Roots rots are promoted by cold, cloudy weather when soils tend to stay wet for longer periods of time which is a very common situation as we move into January and February.

Examine roots for Pythium. AGDIA of Indiana produces on-site serological testing kits that can be used to detect Pythium and Rhizoctonia. If Pythium is detected, materials for control include Subdue Maxx, Alude, Aliette, Truban, and Banrot.

For Thielaviopsis (black root rot) controls include Terraguard, Cleary’s 3336, and Banrot. However, it is recommended that infected plants be discarded. It should also be noted that cleaning used pots or trays with bleach is not enough to protect against Thielaviopsis; you must either steam sterilize them or use fresh ones.

Botrytis- remove spent blooms, water as early in the day as possible, and increase air circulation. Controls include Decree, Daconil, Cleary’s 3336, and Chipco 26019.

Leaf spots- insufficient nitrogen can lead to Alternaria or Colletoctrichum in cold weather and Cercospora in hot weather.

Fungus gnats- can spread root rots. Monitor with potato slices. Controls include IGRs like Adept and Distance. Biocontrols include Bacillus thuringiensis serotype 14 (=israeliensis), available as Gnatrol, and beneficial nematodes (Steinernema feltiae), applied as a drench.

Fertility and pH- the EC should be around 0.5-1.0 microseimens. Maintain a lower pH of 5.8-6.2 to avoid problems with Thielaviopsis and nutrient deficiencies.

Iron deficiency causes interveinal chlorosis on the new leaves and can be corrected with iron sulfate at 2 lbs/100 gallons or sulfuric acid at 1 oz/ 100 gallons.

Boron deficiency makes the leaves thick and puckered and can be corrected with Borax at 0.5 oz/100 gallons or Solubor at 0.25 oz/100 gallons.

Magnesium deficiency can cause symptoms of interveinal cholorosis that look much like iron deficiency. Magnesium can compete with calcium to create a magnesium deficiency that appears on the middle leaves rather than the new leaves. It can be corrected with Epsom salts at 1-2 lbs/100 gallons.

Excess phosphorus and ammonia will cause plants to stretch and become floppy.

Information reprinted from the December 8, 2006 edition of the Greenhouse TPM/IPM Weekly Report from the University of Maryland Cooperative Extension

Landscape - Recommended Plants for Kent County: Kentucky Coffeetree

Kentucky Coffeetree, Gymnocladus dioicus
Photo from the University of Minnesota Agricultural Experiment Station
This is a continuation of a series on recommended plants for Kent county landscapes. Kentucky coffeetree is a very trouble free tree that can be used as a replacement for Norway maple. The following is information on this species.

Kentucky Coffeetree, Gymnocladus dioicus

Kentucky coffee tree (Gymnocladus dioicus) – 60-75’ with a narrow oval crown that tolerates dry soil and urban conditions, short-lived fall color but great bold winter structure.

This is a medium-growing tree that will reach a height of about 70 feet while spreading 45 to 60 feet. The state tree of Kentucky should be used more often because it is adaptable to many soils, has interesting bark and grows with an open canopy allowing light to penetrate to the ground for adequate turf growth beneath the canopy. The coarse branch texture in the winter is also quite unique, forming an interesting silhouette of only several large branches. Large seed pods hang on the tree in the winter but can be a litter problem when they fall in the spring. They are very hard and can be ‘shot’ from a lawnmower running over the fruit. Male trees are sometimes available and they do not set fruit, but this is often unreliable. The seeds (in a 5 to 10- inch-long pod) and leaves may be poisonous to humans. The pod contains seeds which used to be roasted as a coffee substitute. The leaves are bipinnately compound and can be up to 18 inches long, resembling walnut.

The trunk normally grows straight up through the crown and is very strong. Branches grow at wide angles to the trunk and are usually well-spaced along the trunk. This configuration adds to the durability of the tree. Be sure that major limbs are kept at less than about half the diameter of the trunk to ensure that they remain well-attached to the tree. The crown is round or oval in youth, becoming more upright and oval with age. Some people object to the sparse branching when this tree is young, but some pruning to create more branches can help. Any shortcomings of the tree are made up by the almost total lack of insect or disease problems. Lawns grow well beneath the tree due to the light shade cast by the thin, open canopy.

Kentucky Coffeetree is well-adapted to urban soil and could be used more often and, like most trees, does best when provided with irrigation until well established. Amazingly tolerant of drought and poor soil once established although it is native to rich bottomland soil. Used as a street tree in some communities. Be careful using the tree in a lawn since the pods could become projectiles from mowing equipment. Male cultivars without fruit are available to avoid this problem. These will be well-suited for planting along streets. Propagation is by seed, or grafting male plants. There are no pests or diseases of major concern.

Information from the Plants for a Liveable Delaware publication and from the University of Florida Cooperative Extension fact sheet Fact Sheet ST-287 by Edward F. Gilman and Dennis G. Watson.

Saturday, November 24, 2007

Greenhouse - Know the Difference Between Greenhouse Whitefly and Silverleaf Whitefly

Greenhouse growers should know the difference between greenhouse whitefly and silverleaf whitefly. The silverleaf (or sweet potato) whitefly is much harder to control. The following is information on how to identify the two species.

Greenhouse Whitefly: Usually bright white; wings loosely held against body, giving a much broader appearance; forewing with one distinct vein, bent slightly mesad at about middle of wing, and a short distinct ridge forming a fork with the vein.

Greenhouse Whitefly
Photo by Whitney Cranshaw, Colorado State University,

Sweetpotato or silverleaf whitefly: Usually yellowish white; wings tightly held against body, giving a cylindrical appearance; forewing with one vein, bent slightly mesad at about 2/3 of wing, no distinct ridge or trace of fork.

Silverleaf Whitefly
Photo by Scott Bauer, USDA Agricultural Research Service,
Whitefly identification diagrams from the USDA/University of Florida website:

Landsccape and Turf - Know Your Winter Annual Weeds: Chickweeds

There are several chickweeds that are winter annual weeds in landscapes and turf in Delaware. The following are 3 of the most common species.

Common chickweed, Stellaria media
Photo from at Virginia Tech

Mouseear chickweed, Cerastium vulgatum
Photo from at Virginia Tech

Jagged chickweed, Holosteum umbellatum
Photo from

Friday, November 23, 2007

Landscape and Turf - Drought Effects, Educate Your Clients

From a business perspective, client education is very important for long term customer retention. The drought this past year is a good example where you need to inform your customers of future problems to expect related to the severe plant stress this past summer. Take your clients around the landscape and point out problem areas as they relate to the drought stress. The following is an article on the subject.

Of all the problems this season, the drought will have had the most long lasting effect on the landscapes you service. The potential effects of past droughts may not be seen for several years. Be sure to discuss this with clients, and use this knowledge in making decisions about the future, since plants that succumbed to drought must be replaced, and other plants may not show symptoms for months (to years). Take notice where the driest areas are and plan changes to better prepare that area to weather the next drought. If changes are not made, those areas are where future problems are more likely to show up in existing plantings. Trees and shrubs become more susceptible to diseases and insects under drought stress, and these pests will probably attack again next season. For example: Canker diseases which attack now, may not kill off the branch for several years. Borers that laid eggs this season may weaken the tree for several seasons before major damage or symptoms occur. Taking note of the condition of the trees and shrubs this fall can be a good indication of their future potential survival. Examine such plant features as dormant bud health and the distance between terminal bud scars on branches/twigs. If the distance between terminal bud scars is consistently smaller for each of the past few years, then the tree/shrub is undoubtedly experiencing a “declining downward spiral” and may not have the ability to recover.

Article by Steven K. Rettke, Ornamental IPM Program Associate in the Plant and Pest Advisory, Landscape, Nursery, and Turf Edition, Rutgers University.

Landscape - Don't Waste Dormant Season Oil Applications on Dead Scales

Too often, applications of dormant oils go on where scale insects are already dead. The following is an article on the subject.

Live vs. Dead Scale Characteristics:

Many professional landscapers and arborists will be applying early dormant oil applications against over-wintering insect/mite pests. Probably all too often, oil treatments are applied to scale populations that are not viable. Just a little bit of extra time is required to determine if the observed scales are dead or alive. Compare a live, viable scale insect to a water filled balloon. If the cover is somewhat flexible and soft to the touch it may still be alive. Furthermore, with the use of a sharp pinpoint (e.g., insect mounting pin), determine if insect body fluids are released. When the waxy cover of a live armored scale is removed from the plant surface, it will often appear as a red/yellow “blob of jelly.” As an example, by early spring pine needle scale females have already laid most of their red colored eggs and are probably dead (i.e., the female scale has become darkened, dry and shrunken in appearance). Pine needle scale eggs will hatch and red colored crawlers will emerge some time in May. As a side note, do not expect excellent controls of armored scales with the use of dormant oils. Some suppression may occur, but satisfactory results are not always achieved.

Article by Steven K. Rettke, Ornamental IPM Program Associate in the Plant and Pest Advisory, Landscape, Nursery, and Turf Edition, Rutgers University.

Thursday, November 22, 2007

Nursery - Drought and Christmas Tree Plantings

Chrismas tree plantings in Kent County suffered greatly this year because of the drought. The following is an article on the subject.

June through September proved to be very dry throughout most regions of the county. Drought or dry soil conditions result in root damage and death. Non-woody feeder roots, usually located in the top 15 inches of soil, are particularly sensitive and are the first ones affected. Without moisture, these roots shrivel and die. This is expecially severe in our sandy soils. In our heavier soils with high clay content (many Kent county christmas tree plantings are on heavier soils such as our "White Oak" ground), the soil pulls away from the roots as it dries which results in desiccation and killing of the fine roots. When these roots become nonfunctional, a water deficit develops since the roots cannot provide water to the top of the plant.

Effects of drought are particularly severe on seedlings or new transplants because their roots occupy the uppermost layers of soil where the most rapid drying occurs. In addition, recent transplants typically lose feeder roots during the transplant process. Contrary to popular opinion, it often takes woody transplants two years to become completely established in a new site. Therefore, seedling beds and new transplants should be given extra care and attention during periods of drought if possible.

Established trees are also affected by drought, especially those planted in marginal sites such as those in sandy soils or those that have been improperly planted. Drought can exacerbate even the most subtle of improper planting practices!

Symptoms are manifest in different ways depending upon species but are often not evident until some time after the event has occurred--even as much as one or two years later! Symptoms of early drought stress in conifers often appear at the top of the tree as a wilting and drooping of the needles and branches. If dry conditions persist, needles may appear pale and off-colored and can develop "scorch" symptoms or browning at the tips. On spruce, needles become chlorotic and drop. In the case of white pine, needles become discolored and can develop a permanent bend. With most conifers, severely affected needles of all ages will drop prematurely and tip dieback can occur.

Drought stress is especially noticeable in mid-summer on trees in sandy soils or where roots are located in the top layers of heavily compacted soils. Symptoms can develop in individual trees or in groups of trees which are growing under common soil conditions.

In addition to direct root damage, a significant secondary effect of drought is that it weakens trees and predisposes them to secondary invaders and opportunistic pests. For example, it has been reported that root rots and spider mites are more serious on trees under drought stress. Studies have shown that many drought-stressed trees are not as winter-hardy as healthy trees and often develop problems from winter injury. Drought-stressed trees are also more sensitive to air pollutants and pesticides to which they might be exposed.

While there is no cure for this problem, the effects of drought can be minimized by following some preventative measures. Water in periods of low soil moisture: trees require approximately one inch of water per week. This is best applied at one time as a slow, deep soaking to a depth of approximately 12-18 inches. The length of time required to "deep-water" will vary depending on soil type and water pressure: clay soils usually require more time than sandy soils. Frequent, light, surface watering will not help the tree and can actually cause harm by promoting growth of surface roots. A deep soaking just before the ground freezes in the fall will also help the winter hardiness of drought-stressed plants.

Select the appropriate site and follow good planting practices; drought-stress can magnify even the most subtle improper planting practices. Select native plants or match plant species to site conditions: drought-sensitive vs. drought-tolerant species. Prune any dead or weakened tissues to avoid secondary problems. Maintain tree vigor by following good cultural practices.

Modified from "Disease Problems in Connecticut Christmas Tree Plantations" By Dr. Sharon M. Douglas, Department of Plant Pathology and Ecology, The Connecticut Agricultural Experiment Station

Landscape: Dead Branches, Tops, and Dead Trees - The Effect of Water Stress

We have seen considerable drought damage to trees and shrubs this year. Effects of this year's drought will extend well into next year. The following is an article on the subject.


The sudden appearance of dead branches, dead tops, or dead trees can alarm anyone, especially tree growers. In Delaware, these symptoms can be unusually dramatic and are often widespread. The following information describes the damage that is often observed and discusses the usual causes and treatment strategies.


Damage occurs throughout the state, but is most severe in urban areas, on the fringe of forested areas, and on shallow or droughty soil types. Trees growing near roads, ditches, pastures, or in areas of soil disturbance or abundant competing vegetation are most frequently affected. Trees growing beyond their natural range or from non-local seed sources generally are at an increased risk of water stress compared to locally adapted trees or drought-tolerant species.


The most common cause of the damage described above is water stress inside the tree. Water stress results whenever water loss exceeds uptake long enough to cause plant damage or disturb its physiological processes. It usually results from a lack of available soil moisture due to drought, which in turn depends on the water storage capacity of the soil and on the rate at which plants take up water through their roots and evaporate it through the foliage. Water stress often affects groups of trees because they share common soil and environmental conditions that can affect their rate of uptake and the degree of water stress.

Because water storage capacity varies among soil types, water stress will develop in trees on some sites sooner than others under the same weather conditions. Trees exposed to full sunlight and greater air movements tend to lose water faster than trees growing in a closed canopy. Sudden changes in the stand that expose the crown can also increase the rate of water loss or competing vegetation can intercept water from tree roots during periods of low rainfall. Soil compaction can also stress trees by damaging roots, reducing aeration, and preventing water infiltration.

Trees respond to water stress in a number of ways. Moderate levels of stress reduce stem and root growth, while under more severe drought conditions, water content may drop to a critical level where trees are irreversibly damaged and branches, portions of the crown, or entire trees may suddenly die. It is often difficult to gauge the level of stress, as many of the tree's internal responses to water deficits occur without visible outward indicators.


In Delaware, water stress injury usually occurs in mid-summer through fall after trees have formed buds. Periods of greater moisture and cooler temperatures may initially improve tree water balance; however, the warmer conditions of late winter and spring often cause previously stressed trees to rapidly decline. Examinations of discolored branches or tops in early spring usually show little evidence of insects or disease, and are more often the result of water stress the previous year. If damage is due to these other agents, it will usually become more obvious as their activity and development increases in late spring and summer.

Water stress from winter events is also common. Low temperatures, especially following a warm period, can damage sapwood and impair water transport to branches and foliage. Severe needle desiccation and drop, occurs as the result of slower water movement in the soil, along with dry winds and sunny weather that cause increased water loss.

Water stress can also induce the loss of older foliage in the fall. This occurs as the tree mounts a "drought-resistance" response by reducing the total surface area of the foliage and subsequently lowering the rate of water loss.


Healthy, vigorous trees usually resist attacks by insect and disease agents by producing defensive chemical compounds. Tree stress, especially water stress, can reduce the production of these compounds and decrease the tree's ability to withstand attacks.


Populations of insects that attack weakened trees build during or following extended periods of drought or other events that cause water stress.


Several canker-causing fungi also infect and kill branches or stems, giving them an appearance that is often similar to water stress. Cankers are most visible in spring and summer, 1-2 years following water stress, and are distinguished by portions of bark becoming sunken and discolored. Removing a portion of the bark in affected areas reveals dead tissue underneath.


Most tree damage occurs on disturbed sites and is due to a combination of factors including soil conditions, tree species, and weather patterns. It is unlikely that stress will be alleviated by simply altering a single factor. Rather, improvement will come from an accumulation of many moderate changes to relieve stress and increase vigor.

• Prevent soil compaction caused by vehicle or foot traffic near trees. Excess traffic can compact surface soils and damage fine roots, most of which lie within a foot of the soil surface. Clay soils are especially vulnerable.
• Avoid direct damage to trees and roots by machinery.
• Reduce competing vegetation and apply mulch to maintain soil moisture (1-3 inches is usually sufficient).
• Irrigate landscape trees during dry weather. Apply water slowly over many hours so it penetrates to tree roots or use drip irrigation lines.
• Do not alter drainage patterns (ditches, ponds, etc.) near established trees.
• Plant trees that are well suited for the site; use local seed sources and species that are adapted to your soil types.
• If insect larvae or branch/stem cankers are evident, prune and destroy affected branches to reduce the spread of these agents.
• Do not fertilize during drought conditions. Fertilization stimulates foliage production and can increase a tree's water requirements.

Modified from "Dead Branches, Dead Tops & Dead Trees: The Interaction of Water Stress, Insects and Disease", Forest Health & Monitoring Unit, Oregon Department of Forestry

Wednesday, November 21, 2007

Greenhouse - Pesticides for Whitefly Control

Silverleaf whitefly is difficult to control in greenhouses. The following is a table of available pesticides for use in whitefly control in greenhouses, modes of action, and effectiveness on different biotypes of silverleaf whitefly. Click on the tables to get a larger image.

From "Important Update: Control of Q and B Biotype Whiteflies" at

Greenhouse - Whitefly Biotypes

Whiteflies can be difficult to control in greenhouses. The silverleaf whitefly in particular is a problem due to the ineffectiveness of some control measures. In addition, there are different biotypes of these whiteflies that respond differently to control measures. The following is an article on the subject.

The Q biotype whitefly is a new variant of the common A and B biotypes of Bemisia whiteflies, the silverleaf whitefly and sweet potato whitefly. Biotypes are genetically distinct strains of a species, similar to varieties of plant species, although some have been given species designation. Q and B biotypes are visually indistinguishable and require lab tests for accurate identification. Growers' first indication that they have Q biotype is that the usual insecticides are less effective on what appears to be silverleaf whiteflies, not the common and more easily controlled greenhouse white fly. However, it is possible to have mixed populations of B and Q so lack of efficacy may not be clear-cut.

There were at least 6 cases of Q biotype reported from New York State greenhouses in 2006, on poinsettia and hibiscus. If you suspect that you have Q biotype whiteflies, contact your local Extension personnel and they can help you get the necessary lab analysis and treatment options.

Following are some suggestions to growers on managing whiteflies, particularly the Q-biotype whitefly:
  • Carefully check plant shipments for even low levels of whiteflies.
  • Use good non-chemical controls.
  • Correctly identify the whitefly species present!
  • Monitor whitefly population levels as the crop is growing.
  • Use sentinel plants to check for pesticide performance.
  • Consider using biological control right from the start.
  • For unusual silverleaf whitefly control problems, contact a regional Extension specialist for more information on preparing and shipping samples.

From the article "Whitefly Update Q & A (Biotype B too)" by Betsy Lamb NYS IPM in the Ornamental Crops IPM E-newsletter, Spring 2007, Cornell University

Tuesday, November 20, 2007

Greenhouses - Judo, a New Chemical Option for Mite and Whitefly Control in Greenhouses

Judo is a new mite and whitefly control chemical for use in greenhouses. It is of a new and different chemical class and can help with resistance managment. It is very useful for Poinsettias. However, it does show phytotoxicity on some other greenhouse plants so check the label for plant sensitivities and test on a small number of plants before you use it in the whole greenhouse if you have not used it before. The following is an article from New York on using Judo.

Judo is labeled for spider mites, Tarsonemid mites (broad and cyclamen) and Tenuipalpid mites, and greenhouse, silverleaf and sweetpotato whiteflies (see label for specific species). It is reported to be active on all mite development stages, with juvenile stages more susceptible than adults, and to be most active against whitefly nymphs and pupae. Dan Gilrein has found Judo to be effective against the Q-biotype of silverleaf whitefly (Bemisia argentifolii), which is less susceptible to many of the insecticides currently used to manage the A and B biotypes of silverleaf whitefly in the greenhouse, and has the potential to become an increasing pest in New York State greenhouses.

Judo is reported by the manufacturer to be soft on beneficial insects used for biological control. Based on the Koppert Biological Systems website on side effects (check for Side Effects in the left sidebar), it would be appropriate for use with some of the common biological control agents for whitefly or spider mites. Spiromesefin is listed as harmless to Encarsia formosa adults and Amblyseius swirskii adults and eggs. However, it is slightly to moderately harmful to adult Phytoseiulus persimilis. There is no information concerning impact on other life stages of these beneficial insects or on Eretmocerus eremicus or Amblyseius californicus. While Judo has a reported residual control of 20-30 days, depending on the pest species, it has only short residual effects (low persistence) on some of the beneficial species. Persistence is 2-3 weeks for P. persimilis and 0 weeks for A. swirskii and E. formosa, but has not been determined for A. californicus or E. eremicus.

Spiromesefin is a lipid biosynthesis inhibitor in the class tetronic acids and can be rotated with all other labeled miticides for resistance management purposes. It affects water balance in the insect, resulting in desiccation. Feeding stops after 1-2 days and death occurs 4 -10 days after treatment. While no injury has been reported on poinsetia, there is an expanded list (not yet on the label) of plants that show sensitivity to Judo. Other crops require the use of lower rates. Both lists are included on the Judo Product Information Bulletin. Growers are advised to check for phytotoxicity on other crops, as not all crops have been included in the manufacturer's tests.

Reprinted from "New Greenhouse Miticide/Insecticide has Potential for Use with Biological Control" by Betsy Lamb, NYS IPM in the Spring 2007 edition of Ornamental Crops IPM E-newsletter from Cornell University.

Greenhouse - Indicator Plants, Trap Crops, and Banker Plants

Indicator plants, trap crops, and banker plants are biological plant based tools to monitor insect and mite pests, aid in control of these pests, and to maintain biocontrol species. The following is an article on the subject.

Indicator Plants: The diversity of plant species in an area can be used to indicate something about the environment: ground ivy in shady lawns, rhododendrons in acid soil, etc. In the same way, species or varieties that are more susceptible to an insect or disease than the desired crop can be used to indicate when that pest has appeared in the greenhouse. Some common greenhouse examples are potato chunks used to check for fungus gnat larvae (not quite an indicator plant, but the same principle) or specific cultivars of petunias grown as indicator plants for impatiens necrotic virus or tomato spotted wilt virus on a variety of ornamentals. Tomato or eggplant can be used as an indicator of whitefly infestation in poinsettia crops. It is important that the disease or insect be identified rapidly on the indicator plant, before it moves onto the crop, so scouting is still essential when using indicator plants.

Trap crops are also species or cultivars that are more attractive to a pest than the crop, but in trap cropping, the pest is controlled on the trap crop. This system has most often been used in field crops for insect control, where the trap crop is planted around the perimeter of the crop plant to attract insects moving in from outside the field. Some examples are: collards as a trap crop for diamond back moth in cabbage, Hubbard squash for cucumber beetles in other Cucurbitaceous plants, and cherry peppers for pepper weevil in bell peppers. Once the insect is found on the trap crop, only those plants are treated, reducing the amount of chemical pesticide needed. Perimeter trap crops can be used in the greenhouse, but it is more useful to intersperse the trap crop in the desired crop, as it is less likely that insects will be coming into the crop from outside. A set of plants could be positioned near wall vents to monitor insects coming in from outside the greenhouse, however. In addition to tomato or eggplant in poinsettia, gerbera or verbena or a more susceptible cultivar of chrysanthemum have been used to protect chrysanthemum from western flower thrips. The trap crop can be treated before or after it goes into the greenhouse, depending on the chemicals available for use.

Banker plants take the same concept one step further for biological control in greenhouse crops. In this case, the banker plant is used to rear insects that act as an alternative food source for the biocontrol agent, to reduce dramatic changes in its population. The most commonly used banker plant system is a grass, such as wheat or barley, infested with a grass-preferring aphid species, such as bird cherry or corn leaf aphid, to control melon or green peach aphid in ornamental or vegetable crops. The predators or parasitoids are very mobile and can use either the pest population on the crop or on the banker plant as host. There is interest in using the pest population itself as part of a banker plant system, by using the more susceptible cultivar or species, like the indicator or trap crop, as a banker plant. Because the banker plant is infested earlier, predators and parasitoids could colonize it and the population of biocontrol agents would increase before the crop was infested.

Reprinted from "Indicator plants, Trap crops, and Banker plants: Tools for Greenhouse IPM" in the December 2006 edition of the Ornamental Crops IPM E-newsletter from Cornell University.

Monday, November 19, 2007

Landscape and Turf - Vole Damage

Vole damage can be very extensive in landscapes and often is seen in the fall and winter on woody plants. The following is an article on voles and their control.


The meadow vole, also called meadow or field mouse, is a common problem many landscapes in Delaware. These pests can be very destructive to ornamental plantings, including annual and perennial flowers, turf, shrubs and small trees. Voles are compact animals with stocky bodies, short legs and short tails. Their eyes are small and their ears are partially hidden. The underfur is generally dense and covered with thicker, longer guard hairs. Typically, voles are brown or gray, though many color variations exist.

Voles are active day and night year-round. They construct extensive tunnel systems and surface runways. Several adults and young may live in one tunnel system. Populations seem to peak every 2 to 3 years, depending on food availability, climate and other stress factors.


Voles damage plant materials by their feeding habits and their tunnel systems, which can ruin turf as well as interfere with irrigation water patterns. Voles will girdle fruit and forest trees causing commercial damage. They also cause damage to ornamental plants. Their teeth marks are very haphazard leaving no particular pattern on the bark or inner portion of the plant material. Voles will feed on trees year-round with most of their damage occurring in fall and winter. In late summer and fall, they will store seeds, tubers, bulbs and rhizomes for winter feeding.

An extensive surface runway system is the most easily identifiable sign of voles. Vegetation near well-traveled runways may be clipped close to the ground. Feces and vegetation may be found in the runways. Pine voles, also native to Delaware, differ from the meadow vole in that they rely exclusively on a system of underground tunnels.


The best way to control voles is to take their cover away. Voles like vegetative covers or litter piles, because they provide food and cover. Elimination of these areas can help reduce populations. Keep weeds or dense brush away from shrubs and tress. Rake and clean up dead vegetation from areas where runways are seen.

Mechanical: Tree guards of hardware, cloth or other suitable material can be used as a barrier around young trees. Since voles are excellent diggers, place the bottom of the guard 6 inches below the soil surface.

Trapping: Use of snap-type mouse traps may be effective in eliminating small populations or reducing their numbers to reduce their damage. Traps should be placed with the bait side in the runway. Baits of peanut butter and oatmeal or apple slices may be effective. Live traps may also be employed.

Poison Baits: Pelleted commercial baits are effective when placed in the runways or burrow openings. Anticoagulant baits are also effective, though multiple feedings are required for control. Repellents are not usually effective. Such baits should be used only by commercial orchards or nurseries. Other than broadcast and hand placements, baits can be placed in various types of waterproof paper tubes. The tubes should be 5 inches long by 1.5 inches in diameter with the bait glued inside the tube.

Adapted from the Delaware Cooperative Extension Factsheet HYG-62 by Dewey M. Caron, Extension Entomologist

Landscape - Drought Tolerant Perennials

Landscapers may wish to consider more drought tolerant plants for installations. Recently, I posted a list of woody plants with drought tolerance. The following is a list of perennials that have some drought tolerance.


Achillea millefolium, Common Yarrow
Althaea rosea, Hollyhock
Anemone x hybrida, Japanese Anemone
Anemonella thalictroides, Rue Anemone
Anthemis tinctoria, Golden Marguerite
Aquilegia chrysantha, Golden Columbine
Artemisia schmidtiana, Wormwood
Asclepias tuberosa, Butterflyweed
Aster sp., Aster
Baptisia australis, False Indigo
Calamintha, Calamint
Centaurea montana, Perennial Bachelor’s Button
Cerastium tomentosum, Snow-in-Summer
Ceratostigma plumbaginoides, Leadwort
Cimicifuga americana, American Bugbane
Coreopsis verticillata, Threadleaf Coreopsis
Dictamus albus, Gas Plant
Echinacea purpurea, Purple Coneflower
Echinops exaltatus, Globe Thistle
Epimedium spp., Bishop’s Hat
Eryngium spp., Sea Holly
Eupatorium coelestinum, Mistflower
Eupatorium perfoliatum, Boneset
Eupatorium purpureum, Bluestem
Eupatorium rugosum, White Snakeroot
Geranium sp., Cranesbill
Gypsophila paniculata, Baby’s breath
Helianthemum nummularium, Sun-rose
Hemerocallis cv., Daylily
Iberis sempervirens, Perennial Candytuft
Kniphofia uvaria, Red-hot Poker
Lavandula sp., Lavender
Liatris spicata, Liatris
Linum perenne, Flax
Oenothera fruticosa, Sundrops
Papaver orientale, Oriental Poppy
Penstemon digitalis, Beard-tongue
Phlox subulata, Moss Pink
Polystichum acrostichoides, Christmas Fern
Rudbeckia hirta, Black-eyed Susan
Salvia x superba, Perennial Salvia
Santolina chamaecyparissus, Lavender-Cotton
Saxifraga virginiensis, Virginia Saxifrage
Sedum spectabile, Stonecrop
Sempervivum tectorum, Hens-and-Chickens
Silene caroliniana, Wild Pink
Solidago sp., Goldenrod
Stachys byzantina, Lamb’s ears
Thymus serpyllum, Thyme
Vinca minor, Periwinkle
Xerophyllum asphodeloides, Turkey-beard Beargrass


Campsis radicans, Trumpet Creeper
Parthenocissus quinquefollia, Virginia Creeper


Aegopodium podagraria, “Variegatum”, Bishop’s Goutweed
Arctostaphylos uva-ursi, Bearberry
Cerastium tomentosum, Snow-in-Summer
Cotoneaster dammeri, Bearberry Cotoneaster
Fragaria virginiana, Virginia Strawberry
Hemerocallis cv., Daylily
Hypericum calycinum, Aaronsbeard St. Johnswort
Juniperus horizontalis, Creeping Juniper
Liriope spicata, Lilyturf
Sedum sp., Stonecrop
Santolina chamaecyparissus, Lavender Cotton
Thymus serpyllum, Creeping Thyme


Calamagrostis x acutiflora, ‘Karl Foerster’ Feather Reed Grass
Helictotrichon sempervirens, Blue Oat Grass
Luzula sylvatica, Greater Woodrush
Miscanthus sinensis, Maidengrass
Panicum virgatum, Switch Grass

From the publication "Dealing With Drought in the Landscape" by Delaware Cooperative Extension.

Sunday, November 18, 2007

Landscape - How Well do You Understand Scale Insects?

One on the most misunderstood insect pest groups are the scale insects. Because of this, control measures are often ineffective. The following is an article that details the differences between soft and armored scales and the biology of each.

A Large Scale Dilemma

Undoubtedly many arborists, landscapers, nurserymen, and golf course superintendents would agree that effectively controlling scale insects is one of the more frustrating pest management challenges encountered. Of the half-dozen major families of scale insects common in the urban landscape, the armored scales are the most troublesome. With their protective waxy covering, armored scales are considerably less susceptible to various insecticide spray treatments. Many pesticide spray applicators fail to achieve satisfactory controls because they do not have the time or inclination to apply sprays during the scale crawler emergence periods. To complicate matters, the crawler periods for the various armored scale species are quite variable. Furthermore, the improper timing of long residual pyrethroid insecticides can virtually eliminate important parasitoid bio-control activity and hence, often encourage scale infestations. The intention of this article is to stress the importance of properly timed treatments in order to achieve better management of scale insects. This is especially true when attempting to control armored scales.

Scale vs. Scale: Contrasting Armored and Soft Scales Signs and Symptoms:

Without question the two most common families of scale insects found in the urban landscape are armored and soft scales. When physically removed from bark or leaf tissue both soft and armored scale species will leave a white ring of their outer margins. These white rings are waxy adhesives used to closely attach themselves to the plant host. This is an important sign that can be used to avoid making unnecessary treatments against non-scale look-a-likes sometimes seen in the landscape. Soft scales are vascular feeders and secrete large quantities of honeydew that typically becomes associated with black sooty mold. Although the sooty mold is a fungus, it is not pathogenic and is mostly only an aesthetic concern. However, it can be a problem if large areas of leaf tissue become covered, resulting in reduced photosynthesis. No leaf stippling is produced from soft scale feeders since they do not remove green chlorophyll or cause individual plant cell death. As a result, soft scales are less damaging to plant hosts and healthy trees and shrubs can tolerate moderate infestations with little affect. Alternatively, armored scales feed in mesophyll cells of plants and do create leaf stippling and typically cause more damage. They are more likely to generate individual branch dieback and can even kill trees. Since armored scales no not feed in vascular tissues they do not secrete honeydew and give rise to the corresponding black sooty mold.

Feeding Locations:

Most of armored scale species with broadleaf hosts will feed either on bark or leaf tissues, but usually not both (Euonymus scales are a notable exception). The crawlers have only 24 to 48 hours after hatching before they must insert their mouthparts into plant cells and begin feeding. Once armored scale crawlers settle they do not move again for the remainder of their lives (winged adult male scales do change positions, but cannot feed and only live for 24 hours). On the other hand, most soft scale species feed both on bark and leaf tissues during different stages of their life cycles (there are exceptions, especially with coniferous hosts). Unlike armored scales, the soft scales do not lose their legs after the crawlers settle and therefore can move to different feeding locations. On deciduous hosts, the 1st instar crawlers of most species will emerge in June or July from under adult females located on bark. They then move to settle and feed on leaves for the remainder of the summer. Before the leaves drop in autumn the nymphs will move back to bark tissue where they will over winter as 2nd instar nymphs.

Physical Attributes:

Unlike armored scales, soft scales do not produce a detachable protective covering. As a result, soft scale nymphs are exposed to not only sprays, but are easy prey for many predators and parasites. They also suffer high mortality from harsh environmental conditions. Even without insecticide treatments, mortality rates exceeding 98% are typical for soft scale nymphs. To help compensate for these huge losses, soft scale species will lay between 300 to 2000 eggs per female.

The armored scales protective covering is produced by waxy filaments and glue exuded through ducts and pores on the body. Without the protective cover the soft “jelly-like” body of an armored scale would be extremely susceptible to desiccation and predation. This protective covering gives armored scales higher natural survival rates throughout the various life stages and allows for more conservative egg laying. As a result the average armored scale species only produces between 10 to 80 eggs per female.

There are 15 families of scales that have been classified by entomologists. A total of approximately 7,000 species of scales have been identified within these families. More than half of the species (4,000) are included within the armored scale family. It can be said that the family of armored scales have genetically figured out how to best survive and proliferate. Armored scales have reached the evolutionary pinnacle of success.

Reprinted from "Effectively Managing Scale Insect Pests in the Urban Landscape" by Steven K. Rettke, RCRE Ornamental IPM Program Associate, in the March 16, 2006 edition of the Plant and Pest Advisory, Landscape, Nursery, and Turf edition, Rutgers University

Landscape - Control of Armored and Soft Scales

Scale control on landscape plants can be a challenge. This is especially the case with hard or armored scales. The following is some information on effectively controlling scale insects.

Suppressive Treatments: Armored vs. Soft Scales

Soft Scales:

Compared to armored scales, the soft scales are relatively easy to suppress with either contact sprays or systemic treatments. Although large soft scale adult females are more difficult to control, the immature nymphs are highly vulnerable to sprays when good coverage is achieved. There are numerous windows of control opportunities when applying sprays or systemic treatments against soft scales. (1) The best window for control when using spray treatments is toward the crawler emergence period. With only two major exceptions, all soft scale species produce crawlers during the months of June or July. Although scale crawlers are only 2 or 3 times the size of spider mites, they are usually clearly visible without magnification. Most crawlers have a yellowish or reddish coloration. (2) Sprays can also be successfully targeted against the settled 1st instar nymph stage feeding on foliage or bark during the growing season. Achieving adequate coverage to foliage is the major challenge with large deciduous shade trees since the settled nymphs feed on the undersides of leaves along major veins. (3) In addition, dormant oil treatments can be applied in the late fall or early spring to the over wintering 2nd instar nymphs on deciduous hosts. These nymphs have a black or brown coloration and are considerably larger than the crawlers and 1st instar nymphs. They can be observed in clusters on the bark of twigs, branches or trunks. (4) Finally, since soft scales are vascular feeders (phloem or xylem), root absorbed systemic insecticides such as imidacloprid (Merit) or dinotefuran (Safari) have provided better than 90% control rates. Root systemic treatments can be applied as a drench or be soil injected any time during the year as long as the ground is not frozen. Fall or spring applications are most typical. Having adequate soil moisture is a key factor to ensure success when applying root systemic treatments.

Armored Scales:

The primary reason armored scales are so difficult to manage is because the best control windows are dreadfully limited. The covers produced by different armored scale species vary somewhat in their abilities to deter insecticide penetration. Generally the waxy cover greatly reduces the effectiveness of insecticide sprays. (1) The most vulnerable life stage of all armored scales is during the crawler emergence period after egg hatch. The 1st instar nymphs continue to be susceptible to spray treatments for another one or two weeks after settling. However, after this time period most scales species secrete covers to a sufficient thickness to significantly diminish spray effectiveness. (2) Unfortunately, root or trunk injected systemic insecticides provide poor results. Efficacy trials have shown less than 20 to 30% suppression rates. (3) Translaminar materials such as Orthene (acephate) can cause some mortality to armored scales feeding on foliage. They are ineffective against scales feeding on woody tissue. (4) Tragically the traditional use of dormant oil treatments to smother armored scales appears to be overrated. The attempt to achieve satisfactory control by spraying dormant oils is often disappointing since suppression rates are often less than 20%. Therefore to reliably manage armored scales, insecticide treatments must be applied to the crawlers or shortly thereafter.

Research and field observations have determined the time of the year when most landscape scale species have crawler emergence. The most efficient method to monitor for armored scale crawler periods is to use growing degree-day (GDD) emergence periods. The GDD ranges for many common armored scale species are listed in the included table. All scale crawlers on the plant host do not hatch and emerge at the same time, but can range over a period of one, two or more weeks. Consequently, the GDD range represents the span of time the crawlers of a species occur, or when peak emergence takes place.

Conservation of Scale Predators and Parasitoids:

Armored scale infestations in the urban landscape often develop through secondary pest outbreaks. Some of the most effective biological controls found in the landscape are parasitoids against armored scales. When environmental conditions are favorable, parasitoid wasps can very adequately maintain armored scale populations well below thresholds levels. Research studies have shown that cover sprays with broad-spectrum insecticides (e.g., pyrethroids) will often promote scale infestations. These cover or calendar sprays are seldom timed properly against crawler emergence and consequently the treatments are ineffective. On the other hand, these broad-spectrum treatments are death to most beneficials and especially the sensitive parasitoids. Landscape cover sprays over several years duration have shown to increase armored scale populations by a factor of 3 to 4 times compared to landscapes not receiving these types of undesirable treatments. To conserve the important beneficials, the use of horticultural oils during scale crawler emergence periods is most advantageous. Scale species having multiple generations or extended crawler periods may require several oil treatments during the season.

Reprinted from "Effectively Managing Scale Insect Pests in the Urban Landscape" by Steven K. Rettke, RCRE Ornamental IPM Program Associate, in the March 16, 2006 edition of the Plant and Pest Advisory, Landscape, Nursery, and Turf edition, Rutgers University

Saturday, November 17, 2007

Drought Tolerant Trees and Shrubs

Landscapers may want to consider planting trees and shubs that have more drought tolerance. The following are some choices for Delaware.

The species listed below have shown greater drought-tolerance in our area than other species.


Carya ovata, Shagbark Hickory
Castanea mollissima, Chinese Chestnut
Catalpa bignonioides, Southern Catalpa
Celtis occidentalis, Common Hackberry
Fraxinus americana, White Ash
Fraxinus pennsylvanica, Green Ash
Ginkgo biloba, Maidenhair Tree
Gleditsia tricanthos var. inermis, Thornless Honeylocust
Gymnocladus dioicus, Kentucky Coffeetree
Liquidambar styraciflua, Sweet Gum
Platanus acerifolia, London Plane Tree
Populus grandidentata, Largetooth Aspen
Ptelea trifoliata, Hoptree
Quercus coccinea, Scarlet Oak
Quercus imbricaria, Single Oak
Quercus palustris, Pin Oak
Quercus rubra, Red Oak
Quercus stellata, Post Oak
Sophora japonica, Japanese Pagodatree
Sorbus americana, American Mountain Ash
Zelkova serrata, Japanese Zelkova

Small Trees

Chionanthus virginicus, Fringe Tree
Cotinus coggygria, Smoke Tree
Crataegus phaenopyrum, Washington Hawthorn
Diospyros virginiana, Persimmon
Koelreuteria paniculata, Goldenraintree
Pyrus calleryana, cvs. Callery Pear cultivars (not ‘Bradford’)
Sassafras albidum
Syringa reticulata, Japanese Tree Lilac

Evergreen Trees

Cedrus atlantica, Atlas Cedar
Ilex opaca, American Holly
Juniperus scopulorum, Rocky Mountain Juniper
Juniperus virginiana, Eastern Red Cedar
Picea abies, Norway Spruce
Picea pungens var. and cv., Colorado Spruce varieties and cultivars
Pseudotsuga menziesii, Douglas Fir
Pinus flexilis, Limber Pine
Pinus nigra, Austrian Pine
Pinus sylvestris, Scotts Pine
Pinus thunbergiana, Japanese Black Pine

Deciduous Shrubs

Aronia arbutifolia, Red Chokeberry
Baccharis halimifolia Groundsel bush
Buddleia davidii, Butterfly Bush
Chaenomeles speciosa, Common Flowering quince
Hibiscus syriacus, Rose of Sharon
Hypericum kalmianum, Kalm St.-John’s-wort
Ilex verticillata, Winterberry
Jasminum nudiflorum, Winter Jasmine
Prunus x cistena, Purpleleaf Sand Cherry
Rhus typhina, Staghorn Sumac
Rhus glabra, Smooth Sumac
Rhus copallina, Winged Sumac
Rosa rugosa, Rugosa Rose
Vitex agnus-castus, Chastetree
Xanthorhiza simplicissima, Yellowroot

Evergreen Shrubs

Abelia x grandiflora, Glossy Abelia
Buxus microphylla, Littleleaf Box
Ilex cornuta cv., Chinese Holly cultivars
Ilex crenata cv., Japanese Holly cultivars
Ilex glabra, Inkberry Holly
Juniperus chinensis cv. Chinese Juniper cultivars
Myrica pensylvanica, Northern Bayberry
Nandina domestica, Heavenly Bamboo
Pyracantha coccinea, Scarlet Firethorn
Taxus baccata, English Yew
Taxus cuspidata, Japanese Yew
Taxus x media, cv. Upright Yew
Yucca filamentosa, Adams Needle

Taken from the publication "Dealing with Drought in the Landscape" from Delaware Cooperative Extension.

Windbreaks, Screens, Borders, and Hedges

The following is a presentation I developed on windbreaks, screens, borders, and hedges for Delaware.

Double click on slideshow to go to album for larger images and to advance manually.

Friday, November 16, 2007

Landscape - More on Winter Injury in Landscape Plants

The following is another good article on winter injury in landscape plants as we get closer to the winter season.

Direct Low Temperature and Frost Injury:

Plants frequently injured by low winter temperatures are those which are planted in areas north of their appropriate hardiness zone. Such species cannot harden off at an appropriate rate or to an extent sufficient to withstand prevailing winter temperatures. However, even hardy plants can be injured during unusually cold periods or when temperatures drop rapidly or oscillate frequently. If hardy plants are not managed properly (not properly fertilized, pruned, watered, etc.) they may also suffer. Flower buds, vegetative buds, branches, stems, crowns, bark, roots, or even whole plants may be injured. Containerized plantings are particularly vulnerable to low winter temperatures since their roots are not protected by being below ground.

Late spring and early autumn frosts can injure metabolically active tissues that are insufficiently "hardened" to withstand the cold temperatures. This type of injury may occur on native or exotic plants although the latter are usually more valuable. A result of late spring frosts can be the death of dormant but, particularly, expanding flower buds on species such as magnolia or lilac, or the death of young, succulent, actively growing shoots. Cold temperature injury that occurs during winter may not be evident until injured tissues fail to grow the following spring. Management: Avoid planting exotic species north of their plant hardiness zones unless unique microclimates in the landscape are present to guarantee winter survival. Containerized plants should be placed in protected areas, sunk into the ground, grouped together, or heavily mulched to avoid low temperature injury to roots. To allow proper hardening of plant tissues, avoid heavy applications of nitrogen fertilizers in late summer to in-ground plants. Mulch around the bases of root-tender plants (such as roses) to help protect their crowns and roots from freezing temperatures. Even with good management, injury to young growth or insufficiently hardened tissues may still occur as a result of unusual weather patterns. Little can be done to prevent injury in these instances.

Injured and dead tissues should be pruned and discarded or destroyed to discourage invasion of the plants by disease organisms. Replace plants which are completely killed with species adapted for the appropriate plant hardiness zone.

Desiccation Injury:

This type of injury, called "winter drying" or "winter burn", is usually observed in late winter or early spring on evergreen plants. Broadleaved evergreens such as rhododendron exhibit browning or even total necrosis of their leaf margins (leaf scorch) depending on the extent of injury. Narrowleaved evergreens, such as white pine, exhibit slight browning of needle tips when injury is slight. Extensive injury may result in browning and premature abscission of entire needles. The injury occurs during sunny and/or windy winter weather when plants lose water from their leaves through transpiration faster than it can be replaced by roots which are in frozen soil. Management: Plants which are properly watered during dry periods in late autumn are better equipped to withstand this type of injury. Thoroughly watering the soil around plants once every two weeks (once per week for new transplants) during extended dry periods throughout the growing season will also prove helpful. Placing a protective barrier of burlap over or around plants to protect them from winter winds and sun will help to reduce the incidence of this injury. Antidessicant sprays applied once in late autumn and again in mid-winter may also prove helpful.

Winter Sunscald:

This type of injury occurs when the sun warms tree bark during the day and then the bark rapidly cools after sunset. These abrupt fluctuations are most common on south or southwest sides of trunks and branches, and they may kill the inner bark in those areas. Young and/or thin-barked trees are most susceptible to winter sunscald. Management: Wrapping trunks of susceptible trees with protective "tree wrap" is the most effective way to minimize this type of winter injury.

Frost Cracks:

Frost cracks are splits in bark and wood of a tree that result from rapid drops in temperature. They may be associated with internal defects resulting from previous injury to the trunk years prior to splitting. Defective wood does not contract as readily as the outer layers of healthy wood do when winter temperatures plunge rapidly. The strain between the outer, contracting layers of wood and the inner defect causes the outer layers of wood to crack. The initial crack is often accompanied by a loud snap. In winter, the crack may become wider or narrower during colder or warmer periods. Such frost cracks often close and callus over during the summer only to open again in subsequent winters. This callusing and recracking may lead to the formation of large "frost ribs" on the sides of affected trees. Management: Avoid wounding the bark of trees when they are young. Be particularly careful not to bump trees when mowing near them. Mulch around young trees to eliminate the need for close mowing and to help prevent lawnmower injury. Large frost ribs can be braced to prevent reopening during the winter, thus enhancing callusing and healing. frost cracks in trees are ideal sites for the entrance of wood decay organisms. Affected trees should be checked regularly to insure they are free from serious decay and, therefore, not a hazard to surrounding buildings and living things.

Frost Heaving:

Frost heaving of new transplants and small shrubs during the winter will expose plant roots to severe above-ground winter conditions which include cold temperatures and drying wind and sun. Freezing and drying injury to roots, if extensive enough, can result in the death of the heaved plants. Management: Proper mulching around the base and entirely over the root zone of plants will help prevent the soil from frequent freezing and thawing conditions which are most responsible for heaving. Replant heaved plants quickly if possible and mulch around them. Wait until spring to determine the extent of injury and need for replacement.

Snow and Ice Breakage/Injury:

Heavy snow or ice on weak limbs with foliage (as in the case of evergreens) can result in breakage. Even strong healthy limbs of deciduous trees and shrubs can be broken if the weight of ice or snow is extremely heavy. If the ground is saturated prior to a heavy snow or ice storm, and enough weight is placed on the upper portion of a tree, it can lift the root system right out of the ground. (Fig. 2)Management:Prune trees and shrubs to reduce the amount of snow and ice they will collect and/or to eliminate those branches which will be inherently weak. Branches with a wide angle to the main stem are generally stronger and can support more snow and ice than those with a narrow or acute angle. Cabling and bracing of weak limbs on specimen trees by commercial arborists may be helpful. However, removal of such limbs may be the only truly safe measure in many instances. Plant trees and shrubs away from places where snowmelt from roofs will drip on them. Otherwise, the dripping water may freeze on the plants and accumulate sufficiently to break branches. Wooden barriers may be built over small shrubs to allow snow and ice to slide off rather than accumulate.

Extracted from the Cornell University Plant Disease Diagnostic Clinic Factsheet on winter injury.