Wednesday, September 30, 2009

Landscape - Fall Leaf Color 2

The following is the second post in a series on fall leaf color in deciduous plants.

Leaf Senescence

There are popular and scientific myths about the causes of fall color in temperate deciduous forests. Jack Frost is alleged to paint tree leaves with his chilling touch, bringing on color change along with a frosty coating. Another twist on this myth is that Jack Frost brings reds and purples to autumn trees by pinching the leaves with his icy fingers. A less poetic explanation of fall color, favored by scientists for decades, is that the autumnal coloring of leaves was caused by waste products accumulated in the leaves and revealed to us with the fading of green chlorophyll pigments. As it turns out, the waste product theory now seems to be considered a bunch of, well, crud. The fall color pigments are produced, or revealed, only in living leaf cells of deciduous trees during the critical, seasonal process of leaf senescence. In fact, if Jack Frost did his thing too early, or, in other words, if there was an early killing frost, the leaf color display would be dulled, if not stopped altogether.

What triggers these fall changes if not Jack Frost? A specific combination of shortening day length and cooling temperatures in autumn at a given locale is typically “sensed” by plant receptors resulting in the production of plant hormones that initiate leaf senescence. The initiation and timing of the various processes of leaf senescence are genetically controlled for tree populations of a rather narrow climatic zone. How narrow is it? Seedlings originating from a local population in Illinois are usually planted within northern, central and southern seed zones each about 130 miles from south to north. This precise genetic programming, evolving through the impetus of natural selection, allows leaves to escape autumn frost damage in a specific climatic region during senescence. In the western mountains, it is possible to observe the wave of aspen coloration beginning at higher mountain elevations and progressing downwards to milder climates at lower altitudes.

In the living cells of senescing leaves, complex molecules, such as starch and proteins, are broken down into smaller, soluble ones, such as sugars and amino acids, and then exported to storage cells (resorbed). Living storage cells are found in the inner bark of twigs, the outer sapwood of the main stem (in and near wood rays) and in corresponding root tissues. Resorbing and storing these compounds permits the tree to shed its leaves while avoiding loss of the large percentage of their nutrients in leaves. This, in turn, allows the tree to avoid having to compete with other plants and soil microbes for the resorbed nutrients that would otherwise be cycled back into the soil system through leaf litter decomposition. Resorbed nutrients including nitrogen, phosphorus, potassium, sulfur, and carbohydrates. are mobilized from cells and stored within the tree. The following spring the stored nutrients are remobilized and used to support the intense flush of new leaves and spring growth burst in other tissues.

More energy is required for the biochemical breakdown of leaf substances by enzymes, and for loading the soluble products into the leaf-veins for transport out of the leaves, than that which is available as reserves in leaves. Hence it is necessary to protect chlorophyll, at least during the earlier phases of senescence, in order to prolong production of energy rich compounds that initiate the enzymatic reactions necessary for leaf senescence. Additional important biochemical processes supported by photosynthesis in senescing leaves include the production of enzymes and their products that allow leaf cells to better tolerate freezing and drying, that absorb energy from light bursts damaging to the photosynthetic apparatus, that deter leaf predators, that prevent oxidative damage to cell constituents, including membranes, proteins and DNA, caused by free radicals produced during senescence, and that protect and transform the cells of leaf tissue that form the abscission layer at the base of the leaf petiole. The abscission layer allows the leaf to break away cleanly from its branch without forming an opening from which sap could leak and through which disease organisms could enter the tree.

Information from "Why Tree Leaves Turn Color in Autumn" by Jeffrey O. Dawson, Professor of Tree Physiology, Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign. Go to for the full article.

Landscape - Fall Leaf Color 3

The following is the third in a series on fall leaf color in deciduous plants.

Carotenoid compounds

Carotenoid pigments are found abundantly in such vegetables as carrots and tomatoes. The carotenoids include lycopene and beta-carotene, known to be powerful antioxidants and cancer-fighting substances in humans. Another form of carotenoid found in senescing tree leaves is xanthophyll. Carotenoids are responsible for the yellow and orange colors of autumn leaves. The unmasking of the carotenoids accounts for the yellow fall leaf color of Ohio buckeye, yellow-poplar, sycamore, birches, hickories, ashes, and many other tree species.

Carotenoid pigments and chlorophyll are attached to membranes in intricate structures (organelles) called chloroplasts. Chloroplasts give leaves their green color. Carotenoid pigments assist chlorophyll in the capture of sunlight for photosynthesis. The light energy is converted to a form that charges energy-rich compounds needed to activate enzymatic reactions. These yellowish pigments are always present in leaves, but are not visible for most of the year because they are masked by larger amounts of green chlorophyll. As chlorophyll degrades in the fall, the carotenoid pigments degrade more slowly and persist, revealing their yellowish colors.

In pistachio trees undergoing summer leaf senescence in the Mediterranean, S. Munne-Bosch and J. Penuelas of the Science Faculty of the Autonomous University of Barcelona found that carotenoid substances actually increase during the early stages of senescence. Carotenoids are thought to provide both photo-protection and antioxidative protection to the photosynthetic apparatus. Carotenoids dampen damage, caused by high light intensity, to the susceptible photosynthetic apparatus of senescing leaves.

Information from "Why Tree Leaves Turn Color in Autumn" by Jeffrey O. Dawson, Professor of Tree Physiology, Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign. Go to for the full article.

Tuesday, September 29, 2009

Landscape - Fall Leaf Color 1

The following is the first in a series on fall leaf color changes.

During summer, the leaves of trees are factories producing sugar from carbon dioxide and water by the action of light on chlorophyll. Chlorophyll causes the leaves to appear green. (The leaves of some trees, such as birches and cottonwoods, also contain carotene; these leaves appear brighter green, because carotene absorbs blue-green light.) Water and nutrients flow from the roots, through the branches, and into the leaves. The sugars produced by photosynthesis flow from the leaves to other parts of the tree, where some of the chemical energy is used for growth and some is stored. The shortening days and cool nights of autumn trigger changes in the tree. One of these changes is the growth of a corky membrane between the branch and the leaf stem. This membrane interferes with the flow of nutrients into the leaf. Because the nutrient flow is interrupted, the production of chlorophyll in the leaf declines, and the green color of the leaf fades. If the leaf contains carotene, as do the leaves of birch and hickory, it will change from green to bright yellow as the chlorophyll disappears. In some trees, as the concentration of sugar in the leaf increases, the sugar reacts to form anthocyanins. These pigments cause the yellowing leaves to turn red. Red maples, red oaks, and sumac produce anthocyanins in abundance and display the brightest reds and purples in the autumn landscape.

Information from the following website

Greehouse and Nursery - Iron Chelates

The following is a good article on using iron chelates to correct iron deficiencies in greenhouses and nurseries.

Plants take up nutrients only when they are in solution, which can be a problem with iron.At pHs above 6.5, interactions with calcium and other ions in the media solution cause iron to precipitate out of solution and become unavailable to plants.Using iron chelates can keep plants green and growing until you can drop the pH to proper levels.

Chelates can best be visualized as a lobster’s claw (appropriate since the word chelate comes from a Greek word meaning claw) made of carbon and hydrogen atoms holding an iron ion. The more bonds, called ligands, that form between the iron ion and the carbon atoms, the stronger the iron ion is held within the chelate.The strength of the chelate’s hold on the iron ion determines, as pH increases, how long the iron ion will continue to be in solution and therefore available to plants.

There are four commonly used chelates: citric acid, EDTA (Ethylenediaminetetraacetic acid), DTPA (Diethylenetriaminepentaacetic acid) and EDDHA (Ethylenediamine di(o-hydroxyphenylacetic acid)). According to data presented by Norvel (Equilibria of Metal Chelates in Soil Solution, in Micronutrients in Agriculture, Soil Science of America, 1972) citric acid does not strongly bond with iron and is not effective at pHs above 6.0. EDTA strongly holds iron in solution up to pH 6.0, but by pH 6.5, almost one-half the iron is precipitated, and by pH 7.0, almost none of the iron is available to plants.DTPA is an excellent iron source up to media pH 7.0; however, 60 percent of the iron is precipitated and unavailable by pH 8.0. EDDHA is the strongest chelate of any of the commonly used materials and maintains iron availability to plants past pH 9.0. These chelates are ranked in the same order of effectiveness by Drs. Bill Argo and Paul Fisher in Understanding pH Management, Meister Publications.

Chelates prove the maxim “You get what you pay for.” The cheaper the chelate, the less useful it is.You may have to sit down when you write the check for iron-EDDHA, but remember you use very little per plant and you are assured that iron is available to your crop no matter the pH.

Sometimes growers are puzzled by plants showing iron deficiency symptoms when the media pH is only slightly higher than desired.Phosphorus ties up iron and the combination of a weak chelate, slightly high pH and high phosphorus levels can cause iron to be unavailable.Another reason not to over apply phosphorus.

Reprinted from "Selecting which iron chelate to use" by Dean Krauskopf, MSU Extension, Southeast Michigan in the May 10, 2007 Greenhouse Alert newsletter from Michigan State University.

Monday, September 28, 2009

Greenhouse and Nursery - Fall Aster Diseases

Fall asters are being produced and sold along side of mums in many Delaware greenhouses and nurseries. The following are some diseases common on fall asters that you may have to manage.

Aster Diseases
- Leaf spots (Alternaria sp., Ascochyta compositarum, Cercospora asterata, Cercosporella cana, Ramularia asteris, Septoria asteris, and S. astericola). Control watering to avoid prolonged
- Downy mildew (Basidiophora entospora). Control as soon as problem arises with fungicides specific for downy mildew.
- Powdery mildew (Erysiphe cichoraceurum). Mildew that is comonly found on the lower
half of asters. Start control as soon as mildew is apparent using fungicides specific for powdery mildew
- Rusts (Coleosporium soldaginis, Puccinia asteris, P. extensicola, P. grindeliae, P. stipae, Uromyces compactus, and U. junci). Avoid alternate hosts; pines, grasses, and sedges

Gordon Johnson, Extension Horticulture Agent, UD, Kent County

Landscape - Deer Resistant Shrubs

Deer damage is more and more common in Delaware landscapes, especially in newer developments in rural areas. The following is a list of shrubs and climing plants rarely damaged by deer.

Shrubs and Climbers Rarely Damaged by Deer

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 Old Fashion Weigela

Information from the University of Maryland go to for the full fact sheet.

Sunday, September 27, 2009

Nursery - Fall Acclimation for Wintering Over Plants

It is important to acclimatize plants for overwintering in nurseries during the fall months. The following is an article on the subject.

Hardening plants or providing dormancy requires many conditions to occur all at the same time within the plant. Nursery practices like fertilizer applications, irrigation, pruning and light levels all contribute to how successful plants will overwinter and avoid winter injury.

Plants that have a balanced nutrient content overwinter better. Avoid fertilizing plants about six weeks before the average first frost date for your area. Be sure you choose the correct controlled release fertilizer so your plants have lower nutrient levels in the pots over the winter. Research has shown plants prefer higher potassium (K) levels going into the winter. High K promotes cell permeability that is important in avoiding cellular freeze injury. A foliar level of 50 to 75 ppm K is generally sufficient. Field grown plants having soil test levels above 50 lbs./A. is adequate.

Overwintered plants require moisture so be sure to provide enough water to allows some moisture to reach the bottom of the container. Check field stock for moisture availability because a dry September can cause fertilizer that was applied earlier to release when rains do occur causing a flush of new growth. Overwintered nursery stock survival is directly correlated with reduced energy storage due to dry root balls. Dry plants in the fall may not have enough root reserve to break bud and shoot expansion in the spring.

Avoid late season pruning, which may stimulate bud break that ends up causing new growth that is not hardened off. Pruning like fertilization should stop six weeks before the first frost date.

When temperatures begin to drop, most plants slow their growth and begin the winter hardening process which ends up as dormancy. Figure 1 shows this process.

Light levels decrease in the fall, and shorter day lengths signal to the plants that dormancy is starting to occur. Shaded plants acclimate more slowly than those in the sun do. That is another reason for removing shade cloth in the fall.

Be sure to apply protective fungicides to plants being protected for overwintering. A fungicide drench for Pythium or Phytopthora is suggested. Also, a foliar fungicide application is suggested to protect any cut stems, branches or wounds during the hardening off process. If herbicides are used, be sure a safe amount of time has elapsed between application and the covering of poly houses to avoid crop injury.

Information from "Points to ponder as you prepare nursery plants for winter protection" from Thomas Dudek, MSU Extension West Central Region in the September 18, 2009 posting on the Michigan State University Landscape Crop Advisory Team Alert website

Greenhouse and Nursery - Evaluating Alternative Fuels

Many greenhouse and nursery growers are interested in exploring alternative fuel sources and alternative heating systems. Although propane prices are reasonable now, the price spike in 2008 showed what could happen if world demand for natural gas increases again as we come out of recession. It is often challenging to evaluate alternative heating systems. Below are some tables comparing fuel sources and efficiencies from Auburn University. While the information came from the poultry industry, it is very applicable to greenhouse heating.

Tables from the Auburn poultry newsletter. See the link below.

Greenhouse growers can learn a lot from the poultry industry and visa versa. The following are two good articles on evaluating alternative heating systems for poultry houses that can also be used by greenhouse growers.
Newsletter 61 - Alternate Fuel Systems Simple Economics from Auburn University

Biomass Heating Systems...Do They Make Economic Sense? from the University of Georgia

Saturday, September 26, 2009

Landscape and Turf - Fall Soil Sampling

Fall is the time of year that most soil samples are taken by landscapers and turf managers. This is a good service to provide to clients and can help you to explain fertilization and liming programs to clients. The following are some guidelines for taking soil samples.
  • Take soil samples from a uniform depth. Soil tests have been calibrated at the depth of the cultivated layer (6-8 inches) for all but extablished turf. A 7 inch depth should be targeted. This would include areas where new lawns are to be established, flower beds, landscape beds, and areas with trees and shrubs.
  • Established turf should be sampled at a depth of 4 inches.
  • Use a soil coring tool (soil sampling tool).
  • Ideally, a minimum of 20 cores should be taken and composited for a sample. When you mix the cores to form the samples, make sure that you have mixed them well before you take the subsample to send to the lab. All clods or core pieces need to be broken up. The most common mistake in soil sampling is not mixing cores adequately.
  • Take cores in a random pattern in the areas sampled.
  • Divide landscapes up into sampling areas. Beds, turf areas, and garden areas should be sampled separately.
  • If fertilizer has been spot applied to an area (such as fertilizer stakes), samples should stay off of the spots if at all possible. If the spots are not known, then plan to take extra cores.
  • Different soil types within a landscape or turf area should be sampled separately.
  • Avoid any features in a landscape that might skew the test results. Examples would be disturbed areas (such as where pipes were trenched in), wet pockets, or areas right next to pavement or cement walkways. Do not take cores from these areas for the composite. If you are interested in the fertility of these areas, take separate samples.
  • Take samples at least once every 3 years.
  • Target soil sampling at the same time of year each time you take the sample. Time of year is not as important as being consistant in when you take the sample. However, fall sampling gives the most consistant results.

Gordon Johnson, Extension Horticulture Agent, UD, Kent County

Landscape - Azalea Lace Bug

The last generation of Azalea lace bug is now active in Delaware. The following is more information.

Last Generation of Azalea Lace Bug Active

Azalea lace bug (Stephanitis pyriodes), nymphs and some adults are present in Delaware. The adults will be laying eggs in October and the insects overwinter in the egg stage. The eggs are inserted into foliage, usually along the midvein area. We usually see nymphs in May in Delaware and can see at least 2 to 3 generations per year. In southern Delaware where the growing season is a little longer the 3rd generation is more likely. Azalea lace bug populations tend to be highest when plants are grown in full sun and the damage can be the most severe at these sites.

Cultural control: The best thing you can advise your clientele to do is to stop growing rhododendrons and azaleas in full sun and move them into areas of filtered shade or landscapes with shade part of the day. Also, keep pH low with acidic mulch (pine needles, pine bark) and soil moisture even. A stressed plant is more likely to show heavier injury.

Chemical Control: Imidacloprid has been used by most landscape managers for the last decade. Some are starting to use some of the newer neonicotinoids such as Flagship and Safari for lace bug control. The imidacloprid has controlled both species of lace bug for at least a full growing season. We have had several landscape mangers report that they continue to see control carry into a second season.

Photo of azalea lace bug damage by Whitney Cranshaw, Colorado State University,

Adapted for Delaware from an article in the September 25, 2009 edition of the TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers from the University of Maryland Cooperative Extension

Friday, September 25, 2009

Landscape - Oak Lace Bug

I recently got a call from a landscaper describing damage from the oak lace bug. The following is more information.

I recently have seen damage from the oak lace bug in DE landscapes. Oak lace bug adults overwinter under the bark or in leaf litter near the base of the tree. Next spring, look for black eggs and nymphs on the undersides of foliage. At this time of year control is not necessary.

This insect is very similar to lace bugs found on azaleas, hawthorns, and sycamores. Their fall peak of activity is between 1613 3384 [2300 peak] GDD. Stipled leaves have black 'tar spots' on the underside of the leaf. There are two generations per year in our area. Natural enemies often keep this insect controlled, however when treatments are necessary options include acephate, carbaryl, pyrethroids, or imidacloprid. Horticultural oil or insecticidal soap are options when temperature and humidity permit.

Oak lace bug adults and lymphs feeding on underside of white oak. Photo from Michael Masuik, Penn State University.

Lacebug damage on white oak, Quercus alba. Photo from Michael Masuik, Penn State University.

Information from multiple sources: Brian Kunkel, UD; University of Maryland, and Penn State University.

Landscape, Greenhouse, and Nursery - UDBG Landscape Color Trial Garden

The UDBG had an All-American Selections color trial garden again in 2009. Watch for ratings as data from this year is analyzed. The following is more information.

Landscape Color Trial Garden

Located adjacent to the Herbaceous Garden, the Color Trial/All-American Selections Garden features bold sweeps of annual color, combining the newest cultivars with a display of All-American Selections winners that have proven outstanding in national evaluations. The garden offers both home gardeners and industry professionals a chance to observe how up-and-coming plant selections can enliven the landscape with minimal maintenance. For plant suppliers, the garden provides information about how their new selections fare in the mid-Atlantic climate.

UDBG staff conducts bi-weekly evaluations throughout the summer to rate each plant on its performance. Click on the link below to access results and other information for each year.

Coleus varieties in the 2009 color trial garden at UDBG. Photo by Gordon Johnson, UD.

To view 2007 and 2008 ratings go to 2009 ratings will be posted later this year at the same site.

Information from the UDBG website.

Thursday, September 24, 2009

Landscape - Fall Needle Drop in Pines

Inner needle drop is a natural occurance in pines and other evergreens in the fall. The following is more information.

White pines with inner needles turning yellow are not dying, they are just experiencing normal fall yellowing and leaf drop. While evergreens do not loose all their leaves in the fall, individual leaves/needles do not last on the tree forever. If trees are small, you can shake them and loosen the needles. You will end up with a nice pine straw mulch below the trees.

In some years, the natural needle drop will occur in a relatively short period of time, with rapid and noticeable browning of the older needles, which leads to fears the tree is dying. In other years, people don't even notice it happening, because the browning is spread over a long period of time.

The symptoms are normal for the fall. Pines and arborvitaes normally shed their oldest needles in the Fall. White pines usually retain their needles for one to two years. The older needles, those towards the center of the tree, turn yellow before dropping. Older arborvitae leaves turn a reddish brown. Natural needle discoloration may be more noticeable on trees that have experienced root stress due to less than optimal growing conditions. Extended dry periods during the summer months, as well as sites with poorly drained, heavy clay soils may accentuate root stress to pines. Since the newest growth (this year's needles) are still green and healthy in appearance, you can be assured that this yellowing phenomenon is a natural one.

Fall needle drop in pine. Photo from the Plant & Pest Digital Library at Purdue University.

Information from the Ornamentals Hotline Newsletter from UD Cooperative Extension and Gail Ruhl and Jeff Burbrink, Purdue University.

Landscape - Bulb Plant Growth in Fall

It is common for certain spring flowering bulbs to have some foliage growth in the fall. The following is more information.

Some bulbs tend to come up in the fall -- grape hyacinths are a good example. Customers may become concerned that there is something wrong and that the bulbs won’t bloom in the spring. Spring-flowering bulbs have hardy foliage and will not suffer much foliage damage by coming up in the fall. Their flowers won’t come up until spring and will bloom normally. It might be a good idea to cover emerged foliage with a light layer of leaf mulch.

Grape hyacinth foliage dies back following flowering in the early summer, but grows actively again starting in mid-fall. The foliage will persist through the winter. Depending on how severe the winter conditions are and how much protection it receives from snow cover, it may be an attractive element in the winter landscape right up to the time that new growth begins in spring.

Grape Hyacinth in late November. Photo from the Plant & Pest Digital Library at Purdue University.

Information from the Ornamentals Hotline Newsletter from UD Cooperative Extension and Mike Dana, Department of Horticulture and Landscape Architecture, Purdue University.

Wednesday, September 23, 2009

Landscape - Witches' Brooms

Witches" Broom is a term to describe a certain growth abnormality in plants and can have a number of causes. The following is more information.

The development of witches’brooms on woody plants and the resulting formation of abnormal growth can cause curiosity and concern to your clients. Typically, the new growth is distorted and a proliferation of leaves or fruit/cones closely clumped together appears when apical dominance is lost. Witches’ Brooms are created on plants when the transfer of growth hormones is disrupted (perhaps caused from the introduction of a foreign substance). Insects (e.g., aphids), fungi, bacteria, phytoplasmas, and herbicides have all been implicated in causing the formation of witches’ brooms in a large number of plant species. It is interesting to note that sub-lethal doses of glyphosate (Round-Up) when applied late in the season can cause witches’ brooms on new plant growth the following spring.

Witches' broom. Photo from University of Georgia Plant Pathology Archive, University of Georgia,

Information from the September 3, 2009 edition of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition from Rutgers University

Landscape - Boxelder Bugs

Boxelder bugs are nuisance pests that can enter houses in the fall. The following is more information.

The boxelder bug overwinters as an adult in protected places such as houses and other buildings, in cracks or crevices in walls, doors, under windows and around foundations, particularly on south and west exposures. In the spring when tree buds open, females lay small, red eggs on leaves and stones and in cracks and crevices in the bark of female boxelder trees. The eggs later hatch into young nymphs that are wingless and bright red with some black markings. These young bugs usually are found on low vegetation near boxelder trees until seeds are formed on the tree, on which they start to feed.

Boxelder bugs are primarily a nuisance pest, annoying residents by crawling on exteriors and inside dwellings on warm fall and winter days. They also may stain draperies and other light-colored surfaces and produce an unpleasant odor when crushed, but these are not major problems. They do not reproduce during this period. They may attempt to feed on house plants but do not cause any damage. On rare occasions, they have been reported to bite humans.

Types of Control

The most permanent solution to the boxelder bug problem is the removal of female boxelder trees from a neighborhood, although this may not be practical or desirable. Because boxelder bugs usually overwinter near the trees that they feed on, the removal of one or two problem trees may help. Screening or sealing cracks or other entrances into the dwelling is important. Once boxelder bugs have entered the home, control becomes more difficult.

When the bugs begin to congregate on building exteriors, these areas (including all resting and hiding places) may be sprayed with residual insecticides. However, most insecticides registered for treatment of building exteriors are not that effective against boxelder bugs. Laundry detergent and water mixes are cheap, safe and effective when applied directly to boxelder bugs. Drawbacks of detergent sprays are that they will kill only if they contact the insect directly, and they may damage vegetation.

Use a vacuum cleaner to control bugs that have entered the house. Household insecticidal aerosols and many household spray cleaners also are effective when applied directly to individual Insects. These measures provide temporary relief only. Bugs may continue to enter the home as they move about on warmer days throughout the fall, winter and early spring. Nuisance infestations should be finished by late May, as the boxelder bugs have either died or moved back to the host trees.

Boxelder bug adult. Photo by William M. Ciesla, Forest Health Management International,

Information from a fact sheet on Boxelder Bugs by F.B. Peairs from Colorado State University

Tuesday, September 22, 2009

Turf and Landscape - Do Not Let Weeds Go to Seed

I see many lawns with crabgrass and other weeds in seed now. These seeds will be problems for years to come. The following is more information.

Farmers say, “One years’ seeding means 7 years weeding.” This adage indicates how long weed seeds remain viable in the soil. For example, if a soil contains 10,000,000 (ten million) weed seeds per acre, 50% will typically decay per year. Assuming no replenishment through reseeding, at the end of 7 years the population will be reduced to approximately 100,000. This is a lower number, but still significant. Also realize that the weeds that emerge each year often account for less than 5% of the soil’s weed seed population.

Information from the September 3, 2009 edition of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition from Rutgers University

Landscape - Avoid Tree Staking if Possible

There is considerable controversy over whether or not to stake trees. Certainly, top heavy trees, trees with limited root balls, or trees in heavily exposed or windy areas may need to be staked. However, many trees are staked that do not need to be. The following are some facts about staked versus unstaked trees.

No staking is necessary for newly transplanted trees that can stand by themselves or have branches to the ground. Compared to rigidly staked trees, unstaked trees will: develop a 33% greater basal trunk area; grow 19% less in height; develop a 30% greater trunk taper; develop a stronger, larger root system; develop more uniform xylem to support itself upright; have few or no rubbing or girdling injuries.

Guy wires with rubber hose protectors. Left on more than one growing season. Partial stem girdling. Photo by Andrew Koeser, International Society of Arboriculture,

Information from the September 3, 2009 edition of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition from Rutgers University

Monday, September 21, 2009

Landscape - Current Diseases

The following is information on current diseases being found in Delaware landscapes.

Late season leafspots are present on many landscape plants. Septoria leafspot is being seen on many dogwoods including C. sericea, amomum, and florida. Look for grayish angular spots on the leaves. Sometimes they can look like anthracnose but we generally don't see anthracnose here in the fall. Again no controls are needed. Leaf blotch on horsechestnut is another foliage disease that is causing some premature defoliation. Look for the large brown blotches with yellow borders that follow the major veins. Usually it does not affect the health of the tree either.

Leaf blotch on horsechestnut. Photo by Fabio Stergulc, Università di Udine,

Information from Bob Mulrooney, Extension Plant Pathologist, UD.

Landscape - Current Pests

The following are pests that are currently active in Delaware landscapes.

Tuliptree scale and magnolia scale crawlers are active. Horticultural oil and Distance provide good control.

Magnolia scale. Photo by Brian Kunkel, UD Extension

Tuliptree scales. Photo by Gerald J. Lenhard, Louisiana State Univ,

European Hornets/German Wasps and Yellowjackets are very active. They are predatory natural enemies of other insects but may need control, especially where food or food crops are present.

Late season leafhooper and lace bug damage is showing up. On evergreen plants, (Azalea and Andromeda), a fall horticultural oil application may reduce lacebugs and their eggs that would potentially overwinter on leaves.

Information from the September 18, 2009 edition of the Ornamentals Hotline newsletter from University of Delaware Cooperative Extension.

Sunday, September 20, 2009

Landscape - Controlling Fall Invading Insect Pests

The following is information on controlling the 2 common fall insect pests that invade houses: the multicolored Asian lady beetle and the Western conifer seed bug.

Both species (the multicolored Asian lady beetle and the Western conifer seed bug) commonly inhabit the south and west exposures of windows or near places where bright light and heat are present. They appear inside buildings on bright days when temperatures drop below freezing. To manage these fall invaders, exclude entry. Examine doors, windows, walls, soffits, etc. and repair gaps where these insects gain entry. (Note: this also has energy conservation benefits). Vacuuming or sweeping them from inside generally cuts down on almost all but the most extreme problems. Other tactics may include adjusting lighting and color in infested spaces with window treatments, paint colors, or exterior plants. MALB trap designs are available on the internet for extreme cases like laboratories, etc. that need advanced protection. Don't use pesticides against these fall invaders; it provides only short-term relief and does not address bigger structural management issues.

Information from Casey Sclar, IPM Coordinator, Longwood Gardens

Greenhouse and Nursery - New Fall Plant for Consideration

The following is an interesting article from the University of Maryland on a new fall plant for greenhouse sales.

An Interesting Plant for Fall Sales? - Plectranthus

Last week, while visiting Catoctin Mountain Growers, a really fetching purple colored flowering plant caught my eye - Plectranthus. I had not run into this plant before and did a web search for information on this unusual short day blooming plant.

Plectranthus is native to South Africa and a member of the mint family (Lamiaceae). There are many species of Plectranthus (around 44) that are currently used as ornamental herbaceous plants throughout the world's gardens. They come in a number of shapes and colors ranging from white, pink to dark mauves, and lavenders. This plant is easy to propagate from cuttings. The genus of Plectranthus includes common plants such as creeping charlie and Swedish ivy.

Although many of the plants in this genus have a habit of creeping, 'Mona Lavender' has beautiful dark green leaves with contrasting undersides that are purple and very elegant looking. In the 1990's, the 'Mona Lavender' was bred at the Kirstenbosch Botanical Gardens in Cape Town, South Africa. It was a fairly long process involving much hand pollination and the raising of many thousands of seedlings, back crossing, and raising many more thousands of seedlings - each time selecting out the best, most attractive individuals to go through the next round of breeding.

Ball International Company released Plectranthus 'Mona Lavender' plant and it is worth looking into for fall sales. 'Mona Lavender' is a quick-growing perennial shrub, reaching 24 to 30 inches in height but it is not winter hardy here in Maryland. It is ideal for fall sales since customers will need new plants each year. It does very well in either shaded or partly sunny positions. When it receives sun it tends to stay smaller and more compact, and the leaves exhibit a much more intense coloring, especially on the purple undersides of the leaf. The foliage is unique and special, but the real prize on this plant is the dark lavender flower spikes. 'Mona Lavender' is ideal for a mass planting in your garden or for container gardening. Like most Plectranthus species plants need a fair amount of water. The plants benefit from being pinched back to induce better branching and compactness.

Information from the September 18, 2009 edition of the Greenhouse TPM/IPM Bi-Weekly Report from the University of Maryland Cooperative Extension, Central Maryland Research and Education Center. Go to for the full newsletter.

Saturday, September 19, 2009

Landscape - Fall House Invaders 2: The Multicolored Asian Lady Beetle

Asian lady beetles are another problem insect that enters houses in the fall. The following is more information.

The multicolored Asian lady beetle (Harmonia axyridis) [MALB] probably arrived in the US as a result of large-scale aphid biocontrol program releases in the 70's and. It has expanded its range in recent years. These lady beetles are attracted to dwellings that mimic the light stone outcroppings of their native overwintering sites (i.e. white or bright colored houses). MALB feed on a wide variety of pests including hemlock woolly adelgid. However, they have also become a nuisance because they congregate in buildings beginning in fall. Identification of MALB based on color or spot pattern alone is very difficult several different color forms with and without spotting are often present. They will rarely give a small bite.

Different forms of the multicolored Asian lady beetle. Photo from the Pennsylvania Department of Conservation and Natural Resources - Forestry Archive,

Information from Casey Sclar, IPM Coordinator, Longwood Gardens

Landscape - Fall House Invaders 1: The Western Conifer Seed Bug

One common house invader in the fall that clients may call you on is the Western conifer seed bug. The following is more information.

The Western conifer seed bug (Leptoglossus occidentalis) is often found near white pine. It is ¾ inch long looks like a squash bug. They have dusky brown to brownish black bodies and an aggressive looking “beak” head. The upper surface of the abdomen is light yellow to orange. Alternating patterns of brown and black appear at the edges of their wing covers along their backs. While these insects look large and aggressive, they will not bite. They emit a powerful musky odor when disturbed or handled. Adults enter buildings seeking a site to overwinter after feeding on pine or Douglas-fir cones.

Western conifer seed bug adult. Photo by Gyorgy Csoka, Hungary Forest Research Institute,

Brightly colored seed bug nymphs. This stage is common during summer months. Photo by Sandy Kegley, USDA Forest Service,

Information from Casey Sclar, IPM Coordinator, Longwood Gardens

Friday, September 18, 2009

Landscape - Fall is the Time to Control Perennial Weeds and Invasive Plants

Target perennial weed control now in landscapes. The following is more information.

The second half of September is a good time to control many problem perennial weeds using systemic herbicides. At this time of the year, perennial plants have shifted from top growth to moving nutrients downward to areas of the plant involved in winter survival (crowns, roots, rhizomes, bulbs, corms, or tubers). Food reserves are stored in these plant parts and are needed to produce new weed growth in the spring. Systemic herbicides often will be more effective during early fall as they are translocated with this downward movement of nutrients in the perennial weed plant. Early fall applied herbicides also disrupt the downward movement of nutrients by killing foliage thus reducing the amount of carbohydrate that can reach storage organs. Perennial weeds that do not store adequate carbohydrates will have reduced winter survival or will be weakened next spring. Herbicide applications to perennial weeds should be made several weeks prior to the first hard frost for best effect. Examples of early fall perennial weed control programs would be glyphosate on mugwort, fluazifop-P-butyl on bermudagrass, triclopyr on Canada thistle, as well as selective herbicides such as 2,4-D, triclopyr, dicamba and clopyralid for perennial broadleaf weed control in turfgrass.

Now is also the time to control problem invasive woody species like poison ivy, multiflora rose, honeysuckle, bittersweet, fox grape, or porcelain vine. Herbicides containing glyphosate or triclopyr will be effective on these woody invasives as they both translocate readily into root systems this time of year and good control is achieved.

Information from Gordon Johnson, Extension Horticultural Agent, UD, Kent County

Landscape - Premature Leaf Drop on London Plane Trees

London plane trees are losing leaves prematurely at this time. The following is more information.

London plane trees are losing their leaves prematurely and after a close look they have powdery mildew and a leafspot that produces circular non-descript brown spots on the leaves. The spots are numerous and both diseases are contributing to early defoliation. The fungus leafspot is Phyllosticta leafspot and is typically a weakly pathogenic fungus but the cool, wet weather has been ideal and with the trees senescing anyway, the fungus has been very aggressive. Fortunately, it will not cause a decline in overall tree health at this point in the season but is making the trees appear untidy. No fungicide sprays are recommended for this disease at this time.

London plane trees.

Information from Bob Mulrooney, Extension Plant Pathologist, UD.

Thursday, September 17, 2009

Landscape and Nursery - Pictures from the UDBG Perennal Garden

The following are pictures from the UDBG perennial gardens. Photos are of plants that were offered in the fall plant sale.

Landscape, Nursery, and Greenhouse - Pictures from the All American Trial Garden at UDBG

The following are some picture from the All American trial gardens at the UDBG in Newark.

Wednesday, September 16, 2009

Greenhouse - Anthracnose on Pansy

With the wet growing conditions, watch for anthracnose on fall pansy. The following is more information.

Anthracnose on Pansy

The University of Maryland plant diagnostic clinic received a pansy sample with a severe leaf spot problem. Pansies can have a number of foliage diseases, but this time anthracnose, caused by the fungus Colletotrichum, was the culprit. The black setae (hairlike projections) and orange spore masses of the pathogen are often visible with a hand lens in the center of the lesions. Foliar application of fungicides such as the strobilurins (Heritage and others), chlorothalonil (Daconil), or thiophanate methyl (Cleary’s 3336) can protect foliage from anthracnose infection. There are lots of spores in the lesions, and they can be moved by splashing water, so it’s always a good idea to avoid overhead irrigation to reduce disease spread.

Photos below by Karen Rane

Information from the September 4, 2009 edition of the Greenhouse TPM/IPM Bi-Weekly Report from the University of Maryland Cooperative Extension Central Maryland Research and Education Center

Greenhouse and Nursery - Fertilizer Injector Calibration by the Dilution Ratio Method

The following are guidelines for calibrating fertilizer injectors by the Dilution Ratio Method.

Click on text for a larger version in a new window

Information from Chuck Schuster in the September 4, 2009 edition of the Greenhouse TPM/IPM Bi-Weekly Report from the University of Maryland Cooperative Extension Central Maryland Research and Education Center

Tuesday, September 15, 2009

Landscape - Know Your Invasive Plants: Mile-a-minute Weed

The following is information about mile-a-minute weed, an invasive weed in Delaware.

About Mile-a-minute Weed

Mile-a-minute weed (Persicaria perfoliata (L.) H. Gross, formerly Polygonum perfoliatum L.) is an annual Asian vine that invades a variety of habitats in the northeastern U.S. , including forested floodplains, streamside herbaceous wetlands, and upland forests.

Mile-a-minute weed is a prickly, branching, viney annual plant that germinates in early spring, usually in April or May in the mid-Atlantic region. Vines grow rapidly, climbing over other plants, and attain lengths of 6 meters or more. Flowers are inconspicuous, and iridescent blue berry-like achenes are produced beginning in mid-summer and continuing until the plants are killed by frost in the fall. Seeds require a cold period before germinating. Many will germinate within established mile-a-minute patches the following year, while others are spread by birds, mammals, and water. Mile-a-minute seeds can survive for up to seven years in the seed bank.

Mile-a-minute weed. Photo by Leslie J. Mehrhoff, University of Connecticut,

Information from a University of Delaware website detailing research on biological control of this invasive weed. Go to the following site for more information

Nursery, Greenhouse, and Landscape - Harlequin Bugs

Harlequin bugs are active on certain annuals in the landscape and in nursery plantings. The following is more information.

We are seeing feeding activity of harlequin bugs on cleome and snapdragons in landscapes. In the nursery or greenhouse the harlequin bugs are found feeding on ornamental cabbage and kale plants that are being grown for fall sales. Control with Acephate or synthetic pyrethroids such as Astro or Talstar.

Information from the September 11, 2009 TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers from the University of Maryland Cooperative Extension.

Monday, September 14, 2009

Greenhouse and Nursery - Treat for Powdery Mildew

Powdery mildew has really taken off these past two weeks in ornamental plants. I recently received reports of powdery mildew problems on fall asters grown by greenhouse growers with their mum crops. Treatments will be necessary. The following is more information on this disease.

Powdery mildews are one of the most common diseases of ornamental plants; many nursery, flower, and woody plants are susceptible. Greenhouse crops prone to infection include African violet, Begonia , Dahlia , gerbera daisy, Hydrangea , roses, Verbena, Kalanchoe, and poinsettia. Herbaceous perennials particularly susceptible to Powdery mildew include Aster, Centaurea, Coreopsis, Delphinium, Monarda, Phlox, Rudebeckia, and Sedum.

The disease is easily recognizable as a white to gray powdery growth on leaves and sometimes stems and flowers. Powdery mildew may have little or no affect on the plant (other than aesthetic) or it may cause infected leaves to distort, discolor, wither, and defoliate prematurely. Most Powdery mildews have evolved to avoid killing their hosts because they can only survive in living plant tissue. Symptoms and their severity depend upon the cultivar or species of host plant, the powdery mildew species, environmental conditions, and the age of plant tissue when it first became infected. Powdery mildew diseases are caused by species of fungi such as Erisyphe, Leveillula, Microsphaera, Podosphaera, Odium, and Sphaerotheca, although each powdery mildew is specialized to infect only hosts in one genus or one family. Infection does not spread to species of plants in other plant families. Erisyphe has a wide host range and can infect many plants in the Asteraceae family, while Sphaerotheca pannosa var. rosae is confined to roses.

The distinctive whitish powder on leaves is composed of fine threads of fungal vegetative tissue (mycelium) and light colored mats of asexual spores (conidia). Some Powdery mildews produce conidia on short, erect branches that resemble tiny chains, while others form threads so sparse that the mildew cannot be seen without the aid of a microscope. These spores are easily moved by air movement and water splash. Because Powdery mildews are obligate parasites, they do not require plant stress or injury to infect plants. When spores land upon a susceptible host, they germinate and send a specialized feeding structure into the epidermis and obtain their nutrients from the plants. The infection process may take as little as 3 days or as long as 7 days. The pathogen survives in the greenhouse in weed hosts or on crops. Outside, the pathogen can overwinter as mycelium in infected plant parts or in resting structures (cleistothecia) produced by sexual means and visible as small, dark specks on dying leaves. Powdery mildews, unlike most other fungal diseases, do not need free water to germinate and infect. They are favored by high relative humidity (greater than 95%), moderate temperatures (68°-86° F), and low light intensities. The disease is more prevalent in the spring and fall when large differences between day and night temperatures occur. Temperatures above 90° F kill some Powdery mildew fungi and spores and the presence of free water can reduce spore germination.

Monitor crops on a regular basis for Powdery mildew diseases. Epidemics that seem to develop overnight are often the result of undetected low level infections that have spread spores throughout the greenhouse. Rogue infected plants or prune out diseased tissue. Perform this operation when plants are wet or immediately place diseased material into a plastic bag to prevent spores from spreading. The use of resistant cultivars or species is a good management tactic. Although few ornamental crops have been bred for resistance, cultivars of African violet, Begonia, rose, pansy, Zinnia, Monarda, and Phlox with resistance are available. Avoid overcrowding of plants and provide good air movement. Keep relative humidity levels low in the greenhouse by a combination of heating and venting in late afternoon and early morning. Clean greenhouse thoroughly between crops, eliminating all weed hosts and volunteer plants. Unlike most fungi, powdery mildews only colonize the surface of plants making chemical eradication possible. It is not necessary to use fungicides to prevent Powdery mildews. Fungicides with the active ingredients propiconazole (Banner Maxx), myclobutanil (Eagle, Systhane), triadimefon (Bayleton, Strike), fenarimol (Rubigan), thiophanate methyl (Cleary's 3336), potassium bicarbonate (Armicarb, MilStop), or sulfur are registered for Powdery mildew control on ornamentals. Sulfur may cause plant injury if applied when temperatures are high (greater than 85° F). Because the genera and species of fungi causing Powdery mildews are diverse, there may be some variation in fungicide effectiveness across crops. The Powdery mildew fungi can develop resistance to any of the fungicides, except sulfur, listed above so be sure to alternate fungicide applications among chemical classes.

Information from a UMass factsheet on powdery mildew prepared by M. Bess Dicklow, UMass Plant Extension Diagnostic Lab, 108 Holdsworth Hall, University of Massachusetts , Amherst , MA

Greenhouse, Nursery, and Landscape - Powdery Mildew Control Material Trials

The following is a great report on powdery mildew control using fungicides from the Chase Research Gardens. The Chase company is a great resource and has many great products to offer for the horticulture industry. Go to for more information.

Powdery Mildew Chemical Control Update
A. R. Chase Chase Research Gardens, Inc.

I decided it might be a good time to review some of the research on powdery mildew. We spent a lot of time last year fighting with the disease on various crops. First, we could not make it happen no matter what we tried, even on Gerber daisy. Then when we did have the right weather, we could not seem to get any control even with the best products.

Some of our most recent trials were on roses and they really do seem to be one of the toughest crops to control powdery mildew on. We also tested Gerber daisies, crape myrtle and zinnias in this time frame. Results of national trials for chemical control of powdery mildew are summarized in the table below.

It is interesting to see what all of the researchers are testing as well as what specific results are. Eight researchers from Michigan, New York, Alabama and California performed trials on powdery mildew of rosemary, aster, miniature rose, sedum, poinsettia, phlox, Monarda, crape myrtle, azalea, hydrangea, salvia, Gerber daisy, dogwood, Scabiosa, verbena, zinnia and Ranunculus. While this list does not include all ornamentals that get powdery mildew it certainly does show an effort to work on a wide range of crops.

The fungicides that are colored the same belong to the same chemical class. You can see that a few chemical groups are very good to excellent for control of powdery mildew. The sterol inhibitors (in blue), including Banner MAXX, Bayleton, Immunox, Rubigan, Strike, Systhane (now Eagle) and Terraguard, are a key chemical class for fighting powdery mildew. In addition, the strobilurins (in pink), including Compass O, Cygnus, Heritage and BAS500 (an experimental compound from BASF Corporation) are also very effective and have become standards for powdery mildew control on some important crops at least. These two large chemical groups do not even scratch the surface of products for powdery mildew control. Copper products like Camelot and Phyton 27, oils like Triact and Sunspray and potassium bicarbonates like Kaligreen and Milstop also give good results.

One interesting development is the continued use of thiophanate methyl products (in green) for powdery mildew control. These products were excellent for control for years but rapidly developed resistance if they were overused. The results for Fungo, Spectro, Zyban and 3336 show some of this condition. At times they may give excellent control but if resistance to thiophanate methyl has developed for a particular powdery mildew fungus they will not be effective.

As this illustrates, rotation for resistance management is critical. Make sure you use products from at least two chemical groups in an alternating pattern or in a tank mix.


Many ornamental plants are attacked by powdery mildew fungi we have a very large arsenal of chemicals for their prevention. In many cases, we can even eradicate an infection once it is found instead of spraying preventatively. There are a few plant species that are so badly affected by powdery mildew that eradication is not usually effective. For these crops, like some rose cultivars, you should probably spray preventatively when the conditions are favorable for disease.

Information reprinted from "Powdery Mildew Chemical Control Update" by the A. R. Chase
Chase Research Gardens, Inc.

Sunday, September 13, 2009

Landscape - Phytophthora Root and Crown Rot

Phytophthora root and crown rots are very common in landscapes this year. The following is more information.

Phytophthora root, crown, and collar rots are common and destructive diseases of trees throughout the world. Trees declining from Phytophthora root and crown rots are frequently diagnosed as suffering from"wet feet" (mistakenly assumed to be root asphyxiation or "drowning"), and sometimes are confused with those suffering from winter injury.

Diseased trees are most likely to be found in heavy, wet soils or areas where water collects or is slow to drain . Above-ground symptoms are variable among tree species and locations, but include poor growth with sparse off-color foliage, wilt, and collapse. Infected trees may decline over more than one season, and gradually-declining trees often show abnormal or premature coloration of the foliage in early autumn. In other cases, previously-healthy trees may suddenly collapse and die shortly after resuming growth in the spring, especially if the previous autumn was excessively wet. Similarly, previously-healthy trees may suddenly collapse during the latter part of the growing season following a very wet spring.

A diagnostic reddish brown discoloration of the inner bark can be seen by removing several inches of soil around the base of declining trees and cutting away the outer bark layer on the exposed crowns; often, it's possible to see a sharp contrast between the infected and healthy (white) crown tissues. The inner bark of larger infected roots often shows a similar discoloration. These symptoms distinguish Phytophthora root and crown rots from other common causes of decline and collapse.

Red coloration under the bark on a Phytophthora infected tree.

Information adapted from Kearneysville KTFREC - Fruit Disease Focus - Phytophthora Root, Crown, and Collar Rots, West Virginia University

Saturday, September 12, 2009

Landscape - Black Spot on Roses

The following is a good article on black spot on roses from Rutgers University

Black spot, caused by the fungus Diplocarpon rosae (the imperfect stage of this fungus is Marssonina rosae) is the most commonly recognized disease of roses. The disease can cause damage all season long in temperate climates where leaf tissue remains wet for extended periods. Plants chronically affected by black spot become unthrifty and are prone to winter injury.

Black spot is most troublesome early in the growing season. In the spring, fungal spores are produced and disseminated from lesions on canes and leaves infected the previous year. These spores infect young leaves (6- to 14-days old) when a 7-hour period of continuous leaf wetness occurs. Disease development is greatest at temperatures of 75 to 85oF with greater than 85% relative humidity. Symptoms appear as black leaf spots (0.1- to 0.5-inch) on the upper leaf surface within 3 to 16 days following infection. These spots have feathery edges and are accompanied by yellow “halos” of leaf tissue. Spores produced in these spots continue to infect newly expanding leaves and canes throughout the summer. Black spots may also form on the lower leaf surface about a month following infection. On first-year canes, irregular, raised, red-purple blotches appear that become blackened and blistered. Diplocarpon produces a toxin that causes affected leaves to turn yellow and defoliate prematurely. Indeed, heavily infected plants lose much of their carbohydrate reserves, and as mentioned above, grow poorly as a result and become more susceptible to winter injury and other stresses.

Since the fungus overwinters on diseased leaves and canes, rake old leaves and prune diseased and damaged canes before spring. Avoid overhead watering and excessive shade, and when planting, space plants to avoid excessive humidity. Disease management before the growing season begins is critical; control is difficult once black spot is established in a planting. Resistance to black spot varies among the different types of roses. Floribunda, shrub, and climbing roses tend to be more tolerant to this disease, whereas hybrid tea, grandiflora, and miniature roses are more susceptible.

For best results, spray fungicides after budbreak (mid-May) and repeat at intervals specified on the label. Compounds labeled for black spot control include Armada, Bacillus subtilis, calcium polysulfide (dormant) captan, chlorothalonil, Concert (outdoors only), ConSyst, copper (Badge, hydroxide, metallic, salts, sulfate), ferbam, Junction, mancozeb, maneb, myclobutanil, neem oil, paraffinic oil, propiconazole (outdoor use only), Spectro, Sporan, sulfur (dusting, elemental, flowable, wettable), SysStar, thiophanate-methyl, trifloxystrobin, ziram, and Zyban. Use a surfactant to enhance fungicide coverage if this practice is listed on the fungicide label, and rotate classes of chemicals to reduce the likelihood that fungal resistance to compounds will develop. Pay close attention to spray practices during wet periods, especially when caring for roses that are highly susceptible roses to this disease.

Black spot on rose leaves with feathery purple/black spots having no definite margin. Photo by Paul Bachi, University of Kentucky Research & Education Center,

Information from Ann B. Gould, Ph.D., Specialist in Plant Pathology, Rutgers University. See the full article including other rose diseases at

Nursery - Forage Radish Cover Crop For Improving Growth of Trees in Nurseries

The following is a good article on using forage radish as a cover crop in nurseries from the University of Maryland.

Forage Radish: For improving growth of trees in nurseries

Forage radish, also called tillage radishes, is from Daikon radish, which is a traditional Japanese radish. Daikon radishes have been grown for human consumption for a very long time but are being used more and more for natural weed control. The tillage radish is extremely competitive and will outgrow most other weeds. The seed rate is 1 lb per 4000 ft2 and is seeded in September or October. The seed germinates very quickly and light green foliage will expand to cover about 12 – 18” of soil surface. The radish that is produced is huge. It is several inches in diameter and will grow several feet into the soil profile. I (Stanton) have been playing with forage radish at my farm for the last two years. I plant it at the base of fruit trees and blueberry plants where I usually have problems controlling weeds. So far it is working fairly well. It competes with most weeds except Canadian thistle which still manages to thrive even in thick plant of forage radish. In December the plants die down and the root will die over the winter. As the large root dies it leaves an excellent column of organic material in the soil and adds nitrogen back to the soil as it decomposes. If you attend the October 2 Sustainable Nursery Field Day at D.R. Snell Nursery, Inc. you can learn more about the trials the University of Maryland is conducting on the tillage radish in nursery plantings. Do a web search for Daikon radish or tillage radish and you will find seed sources. I bought my seed from Groff seed in Holtwood, PA

Information from Stanton Gill, Extension Specialist, IPM for Nursery, Greenhouse and Managed Landscapes, University of Maryland

Friday, September 11, 2009

Greenhouse - Scouting for Insects and Mites

The following is a good article on scouting for insects and mites in the greenhouse from Rutgers University.

Scouting Options and Methods

There are essentially three options available when scouting your greenhouse crops for insect/mite pests. 1- No scouting performed with pesticides being applied on a calendar timetable. 2- Simply scouting for pest occurrence with pesticides applied when presence is observed. 3- Scouting crop and making pesticide application decisions based on pest counts and action thresholds. The third option is part of an integrated pest management (IPM) approach that has been promoted throughout the green industry the past few decades. Greenhouse pest populations are measured by trapping or direct plant inspection and both involve determining pest numbers.

Counting pests and using action thresholds requires time and knowledge, but results in less pesticide use and can improve plant quality. It is important to remember that trapping (e.g. yellow or blue sticky cards) improves the efficiency when scouting your greenhouse, but does not replace the actual inspection of individual crop plants. This is particularly the case when scouting for aphids and mites. Benefits of Counting Pests The scouting and counting of insects/mites helps to detect when they are first present. Therefore treatments are made before large populations build up, but not before it becomes necessary.

Tracking pest numbers over a period of time allows for the use of action thresholds, or when pest density levels threaten crop salability and economic loss. When pest densities and damage are low, it is not efficient to spend 95% of your time controlling the last 5% of the pest.

The use of biological controls (e.g., beneficial insect/mite augmentation) is most effective when pest numbers are low, and scouting helps to know their density and location so that natural enemy release can be targeted. When using biological controls, pest count estimates are required in order to determine how many beneficials to release per target management area. Finally, instead of guessing, scouting and estimating pest counts makes it possible to evaluate the effectiveness of pest control interventions after they are applied.

Using Sticky Cards to Trap Adults

Generally one (1) sticky card is placed within each 1,000 sq. ft. area and also near greenhouse vent and door openings. Ideally the card should be placed at the level of the crop canopy or slightly below to effectively trap many of the major adult pests found in the greenhouse. Each of the sticky cards should be examined at least once per week. Using stakes and double clothespins to support the traps is effective. Also, be certain to number and date each trap card to a specific location. When pest counts are low it is acceptable to re-use the trap card for additional weeks.

Yellow sticky card

Information from "Pest Counts and Action Thresholds in the Greenhouse" by Steven K. Rettke, Ornamental IPM Program Associate, Rutgers University in the August 20, 2009 edition of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition; A Rutgers Cooperative Extension Publication

Greenhouse - Monitoring for Spider Mites

The following is information on scouting and monitoring for spider mites in the greenhouse.

Monitoring for Two Spotted Spider Mites

Obviously, since spider mites are unable to fly during any life stage they will not be observed on sticky traps. Hence, when scouting for mites it is necessary to inspect individual plants within the crop. Looking for symptoms and signs such as leaf stippling and webbing help to indicate which plants to inspect more closely with a 15x magnifying hand-lens.

Some specific thresholds of two-spotted spider mites on ivy geraniums have been determined through research. It was shown that action thresholds of 7 mites per leaf are reached on plants greater than 5 weeks in production. Alternatively, action thresholds of only 2 mites per leaf are reached on plants less than 5 weeks in production. Estimated pest mite counts are required when releasing beneficial predatory mites (e.g., Phytoseiulus persimilis). Release one (1) predatory mite for every 4 to 10 twospotted mites counted

Two spotted spider mites. Photo by Frank Peairs, Colorado State University,

Information from "Pest Counts and Action Thresholds in the Greenhouse" by Steven K. Rettke, Ornamental IPM Program Associate, Rutgers University in the August 20, 2009 edition of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition; A Rutgers Cooperative Extension Publication