Landscape - Oak Galls

Yesterday, a sample of an oak twig with galls was brought in for identification. Galls can be caused by pathogens and insects. Oaks are particularly susceptible to insect galls. The following is information on common galls caused by insects in oaks in Delaware.

Oak trees have a number of galls. Gouty oak gall is caused by a tiny wasp (order Hymenoptera). Most frequent on red oak the gall occurs on many other native species. Galls form on twigs and coalesce to form a long mass on the branch. Control is not usually necessary.

Another oak gall seen mainly on white oak is wool sower gall; the insect pest involved is a tiny wasp (order Hymenoptera). The insect stimulates the twig to produce a rough, shaggy, reddish globular gall 1 to 1 1/2 inches in diameter. Gall becomes covered with creamy-white growth of fibers like wool, turning light brown with age. Control is not usually necessary.

Another oak gall, mainly pin oaks is horned oak gall; the insect pest involved is a tiny wasp (order Hymenoptera). Infested twigs of pin oak usually have several galls forming an irregular woody mass of 2 or more inches. Tgall is covered with numerous conical, hollow horn-like projections. Control is usually not necessary.

On white nut and scrub oak is oak bullet gall; the insect pest involved is a tiny fly (order Diptera). It occurs on small branches with galls bullet-shaped and 1/3 to 2/3 inch in diameter. They usually occur in groups of two or three. Galls are yellowish in color, tinged with red. Control flies that emerge from galls in October with a general-purpose insecticide.

On numerous oaks are oak-apples; the insect pest involved is a tiny wasp (order Hymenoptera). Spherical galls are found on leaves and twigs. They have a strong outer wall, 3/4 to 2 inches in diameter and are usually fastened to a vein or leaf petiole. Control is not usually necessary. On bur oak and swamp white oak are found noxious oak gall; the insect pest involved is a fly maggot (order Diptera). Galls form on the leaves and later on the stems. Galls vary greatly in shape but are more or less tuber-like. They deform the branches. Cut and burn all twig galls before the first of March. Insecticide spray may do more harm than good by killing beneficials.

Extracted from "Gall Insects" by Dewey M. Caron, Extension Entomologist and Derby Walker, Extension Agent (retired), University of Delaware Cooperative Extension. Go to http://ag.udel.edu/extension/horticulture/pdf/ent/ent-03.pdf for the full fact sheet.

Landscape - Yard Waste Ban in New Castle County

The following is information on the yard waste ban in New Castle County for waste that enters the Cherry Island Landfill.

Yard Waste in New Castle County

There has been a lot of interest recently in New Castle County in the new Yard Waste Ban that goes into effect on January 24, 2008. Here are some details:

This ban is only for yard waste entering the Cherry Island Land Fill. It was imposed as part of the permitting process for the landfill. Over the next several years, other landfills in Delaware will renew their permits and yard waste bans will probably be imposed at that time. The intention is to increase the life of the Cherry Island Land Fill (and others in the future) since 23% of the residential waste stream is yard waste and yard waste can be recycled and reused as compost.

Currently, this ban only affects residents in New Castle County whose trash haulers use the Cherry Island Land Fill (most of northern New Castle County). So the first step for residents is to check with their trash hauler. Landscapers who need to dispose of yard waste can bring the waste to the Cherry Island Land Fill where it will be composted on-site. The tipping fees will be the same as for other waste. Landscapers can also bring yard waste to private entrepreneurs who accept and compost yard waste. Strobert’s Tree Service (475-7089) is accepting yard waste and the tipping fees are less than at the land fill.

Residents should understand they have three choices for dealing with yard waste:

1. Compost and use it on site - this is the best alternative since it doesn’t involve using resources for transport of the waste.
2. Take it to a land fill or composting location yourself.
3. Pay a trash hauler or landscaper participating in yard waste collection services to pick up the yard waste and take it to an appropriate site (depending on the trash hauler, this service may be provided at no additional charge or there may be an additional fee for yard waste pick up).

DNREC is currently working with trash haulers and landscapers in the state to identify the services they will be providing to their customers. A list of yard waste drop-off sites, collection options, and other up-to-date information is available at the DNREC website: http://www.dnrec.delaware.gov/yardwaste.

Reprinted from "Yard Waste and Composting" by Dot Abbott, Susan Barton, and Carrie Murphy, University of Delaware Cooperative Extension. Go to http://ag.udel.edu/extension/horticulture/pdf/hyg/hyg-97.pdf for the full fact sheet.

Landscape - Canker Diseases on Woody Plants

Late winter is a good time to inspect trees and shrubs for canker diseases and remove any infected branches. The following is an article on the subject.

Late winter is a good time to prune-out diseased, dying, and dead twigs and branches to improve plant appearance, to reduce disease spread, and reduce pathogen inoculum. Canker diseases on twigs and branches may be easier to see now before emerging foliage obscures them. For some canker diseases, pruning while the plant is still dormant may be the last opportunity to prune without danger of spreading the disease.

What are cankers? Cankers are localized dead areas of twigs, branches, limbs, trunks, and even roots of woody plants. They are often caused by invasion of bark or cambial tissues by fungi or bacteria which then kill phloem, cambium, and the outermost xylem. The bark in an infected area may shrink, crack, and expose the wood beneath. Canker diseases often girdle the infected branch, causing the entire branch to die. Infection occurs through wounds such as mechanical injuries, leaf and fruit scars, branch stubs, and cold-injured or sun-scalded tissues. Many fungi and bacteria that cause cankers normally inhabit the surface of the tree, or possibly exist inside the tree as latent pathogens, and only cause disease when the tree is under stress. However, some fungi and bacteria aggressively attack trees and cause cankers. Cankers, or dead areas on the bark not involving pathogenic microbes, can also be caused by mechanical injuries such as hail, heat, or cold.

Perennial cankers.

Target-spot cankers caused by fungi such as Nectria or Eutypella on hardwoods are roughly circular or elongate with much callus at the canker edges. Wounds and branch stubs are invaded by the fungus during the tree's dormant period. The plant forms callus around the infection site during the growing season, but the fungus invades more tissue the following dormant period. This back-and-forth struggle between the tree and the pathogen creates concentric ridges of callus tissue. Although infection spread is relatively slow and target cankers seldom kill the tree, they do weaken the tree structure and detract from its appearance.

Annual cankers.

Weak parasites normally don't cause disease problems unless the tree is under environmental stress and low in vigor. Infection occurs during the dormant season, but during the growing season host callus tissue walls off the canker and prevents further spread. Although annual cankers do not persist, continued stress makes it likely that more cankers will form and it opens the possibility of invasion by other diseases.

Diffuse cankers.

Fungi such as Cytospora, Botryosphaeria, Hypoxylon, Phytophthora, or Cryphonectria (chestnut blight) and bacteria such as Erwinia (fire blight) produce cankers with little callus at the margins. Because the pathogens invade so rapidly, the tree tissue at the canker margin is killed and branches or whole trees are girdled and killed, sometimes in one season. Some diffuse cankers are favored when the tree is under stress, but most are not. Canker blights are diffuse cankers in which the disease develops rapidly and kills collateral branch and foliage tissue by way of girdling; canker-rots are diffuse cankers that cause significant internal wood decay.

Common fungal cankers include:

Botryosphaeria canker of many kinds of trees and shrubs
Cryphonectria canker of chestnut (chestnut blight)
Cytospora (Leucostoma) canker of fruit trees and spruce trees
Discula canker of dogwood (dogwood anthracnose)
Hypoxylon canker of oaks
Nectria canker of many kinds of trees
Phomopsis canker of a variety of trees and shrubs
Seridium canker of Leyland cypress
Sphaeropsis canker of Austrian and Scots pines (pine tip blight disease)
Thyronectria canker of honey locust and other woody plants

Pine tip blight, dogwood anthracnose, and chestnut blight are observed to kill trees or at least cause significant dieback. The most common bacterial canker occurs mainly on apple, crabapple, pear and flowering pear and is caused by Erwinia, the fire blight bacterium.

Canker disease management.

For canker disease management, integration of several cultural practices may be needed. Inspect woody plants in the nursery and landscape for cankers. Look for: dead twigs and branches, especially the area between diseased and healthy tissue localized areas of roughened or cracked bark, especially around wounds and branch stubs ridges of callus formation small red, dark brown, or black pimple-like fungal fruiting bodies in the center of, or around the edges of, the cankers. Prune-out cankers during dry weather, preferably when trees are dormant, and avoid pruning during the growing season when canker fungi may be active. When pruning, be careful to avoid damage to the branch collar. Plant well-adapted species and cultivars, matching the plant with the site. Use proper transplanting techniques.

Promote tree vigor so that the tree's natural resistance to disease can be expressed and wound healing can begin promptly and develop rapidly. Apply mulch, water plants during dry periods, and aerify compacted soil. Apply fertilizer only where there is a known mineral element deficiency. General fertilization, especially with nitrogen, can make some canker diseases worse. Control weeds and other competitors, but avoid herbicide injury. Prevent mechanical injury. Protect trees from defoliating insects and diseases. Remove trees weakened by cankers.

Adapted from "PRUNE-OUT CANKER DISEASES FROM LANDSCAPE TREES AND SHRUBS" By John Hartman in the March 21, 2005 edition of Kentucky Pest News from the University of Kentucky College of Agriculture.

Landscape - Lichens on Tree Trunks

Lichens can be found growing on tree trunks, sometimes causing concerns by homeowners and property managers. However, lichens are generally harmless. The following is an article on lichens.

Homeowners sometimes ask: Is that profuse, greenish, crusty stuff growing on my tree a disease? Is that crusty, green or gray material that covers the bark of tree trunks and branches going to harm the tree? What are those leathery things covering the tree bark? The short answers are that the grayish-green crusty things are lichens and that lichens are not tree parasites.

Lichens often appear as a perennial green or gray coating on the trunks and branches of trees. They are actually two organisms in one, being composed of a fungal body harboring green or blue-green algae, which live together in complete harmony. In the symbiotic relationship, the algae, through photosynthesis, supply carbohydrate food to the fungus and, in turn, receive protection and trapped water and mineral elements from the fungus. In this relationship, the algae and the fungus are not distinguishable except with a microscope, and the lichen persists longer than the alga or the fungus would separately.

Lichens do not parasitize trees, but merely use the bark as a medium on which to grow. In fact, lichens can be seen growing on rocks, weathered lumber, or on dead branches fallen from the tree. Some may consider lichens unsightly, but they are not generally injurious except that, when extensive, they may interfere with the gaseous exchange of the parts they cover. Because of their extreme sensitivity to sulfur dioxide air pollution, lichens seldom appear on trees in industrial cities... They rarely develop on rapidly growing trees, because new bark is constantly being formed before the lichens have an opportunity to grow over much of the surface. Because of this, lichens on certain species may indicate poor tree growth. We have noticed that in some plantings, those trees that are more vigorous have fewer lichens than those of the same age nearby in a state of decline. Few studies have been conducted to verify any correlation between lichen growth and tree vigor.

Lichens on trees take on various forms. Some are closely appressed to the bark surface and are described as crustose. Lichens which are foliose have leaf-like lobes which extend out from the bark surface. Others have hair-like or strap-like forms and are referred to as fruticose lichens. Lichen color may include forms that are green, blue-green, yellow-green, brown, gray, or even red. Increases in lichens are sometimes associated with moist climate - perhaps the relatively moist weather of the past two summers accounts for increases in lichen questions. Lichens proliferate when more light is provided, which could explain why they are more frequently seen on dead, leafless branches.

As a rule, lichens can be eradicated by spraying the infested parts with Bordeaux mixture or any ready-made copper spray. Read the fungicide label to be sure that this use is permitted for the product chosen. However, suppression of lichens with chemical sprays should not be expected to improve tree health.

Reprinted from the article "LICHENS INFESTING TREE TRUNKS AND BRANCHES" By John Hartman in the March 7, 2005 issue of the Kentucky Pest News from the University of Kentucky College of Agriculture.

Landscape - Effects of the 2007 Drought on Landscape Plants in 2008

The drought of 2007 will have long lasting effects on woody landscape plants. The following is an article on the subject.

2007 Drought effects on landscape plants in 2008.

Woody plants.

Wilt and leaf scorch symptoms are often associated with dry weather. In addition, drought-stressed plants close their stomata which reduces their rate of photosynthesis. Reduction in photosynthesis may not kill a tree or shrub, but it means fewer carbohydrates are made and stored for future use. In the landscape, seedlings and recently transplanted trees and shrubs were at greatest risk because they lacked extensive root systems.

With drought, there are some fungal diseases of landscape trees and shrubs that often do not show symptoms until the following season, after the drought has passed. The role of water stress in encouraging opportunistic plant pathogens is unclear. It is possible that the stress condition interferes with the plant's defense against such pathogens, or possibly, the reduced carbohydrate reserve allows the plant little energy to fight invasion by pathogens.
Expect certain fungi such as Hypoxylon, primarily an oak pathogen, and Armillaria, which attacks many woody plants, to appear in 2008 because of the 2007 drought stress. In addition expect symptoms of diseases caused by other fungi such as Thyronectria, (honey locust canker); Cytospora or Valsa, (cankers on prunus, poplar, willow, maple, spruce and other conifers); Diplodia, (pine tip blight); and Botryosphaeria and Nectria (cankers of many woody plants such as rhododendrons, crabapples, dogwoods, maples, and others) to appear the season following the dry weather.

In searching for water, some woody plants could have sacrificed surface roots to the drought while relying more heavily on roots that were deeper in the soil. If excessive rains return, partial flooding could render these deeper roots more prone to root rot diseases, thus leaving the woody plants with few functional roots. Thus, expect additional woody plant death when the drought breaks.

One possible benefit of the drought could be the reduction in foliar diseases this year. There could be less carry-over inoculum from shade tree anthracnose diseases, crabapple scab or rose black spot, for example. The benefit could be short-lived, however if spring weather is wet and rapidly repeating cycles of these diseases occur. Looking ahead even farther, the rust infections of cedar that should have occurred, but didn't, during the dry 2007 summer might result in fewer cedar galls in the spring of 2008 and less rust on crabapples and hawthorns that same summer.

Herbaceous ornamentals.

Perennial flowers and ground covers, like their woody counterparts could have reduced energy reserves due to the drought. This could make them more susceptible to cankers and to root, corm, or bulb rot diseases. There is not much research on the role of stress on diseases of herbaceous ornamentals, so it is difficult to know how the drought will affect these plants. A few diseases such as Volutella blight of Pachysandra, are known to be more severe on stressed plants, but most likely the disease would have appeared during the drought. For foliar diseases, the situation is similar to that of woody plants - reduced primary inoculum might result in less disease, at first.

Adapted from "HOW WILL THE DROUGHT OF 2005 AFFECT LANDSCAPE PLANT DISEASES?" By John Hartman in the March 6, 2006 edition of the Kentucky Pest News from the University of Kentucky College of Agriculture.

Landscape - Recognizing Diseases on Perennials and Annuals in the Landscape

The following are some tips on recognizing diseases on perennials and annuals in the landscape.

Infectious plant diseases in the landscape are caused by pathogenic microbes such as fungi, bacteria, phytoplasmas, and viruses. Symptoms such as wilt, leaf spot, root rot, canker, and blight resulting from microbial infections represent the plant's reaction to disease. When evidence of the pathogen such as fungal spores or mycelium, bacterial ooze, or fungal fruiting bodies can be seen, they are regarded as signs of disease. Foliar diseases of landscape plants are most noticeable and they can often be identified by symptoms seen by the unaided eye and signs visible with a hand lens.

Rust diseases.

Rust diseases often produce raised pustules on the leaf surface which produce spores which are distinctively brown, reddish brown, orange or yellow in color. Infected leaves often produce a yellow spot with pustules that are found on the undersides of infected leaves. Rust diseases are favored during wet weather with moderate temperatures. Heavily infected leaves become yellow, then turn brown and die. In Delaware landscapes, rust can commonly be found on aster, daisy, dragonroot, geranium, hollyhock, jack-in-the-pulpit, rudbeckia, snapdragon, and sunflower.

Leaf spot diseases.

Leaf spots caused by fungi or bacteria are common on annuals and perennials. Symptoms vary depending on the host and the pathogen, but common leaf spot forms include angular brown or gray spots, brown spots with yellow halos, irregular blotches, tan or gray spots with reddish margins, reddish streaks and target-shaped circular spots. Some of the spots may contain tiny black pimple-like fungal fruiting structures called pycnidia. These pycnidia, as seen with a hand lens, are visible signs of disease. Spots may coalesce and blight affected leaves and heavily spotted leaves usually shrivel up and die or drop from the plant. Fungal leaf spot diseases are favored by wet, rainy seasons or frequent overhead irrigation. Examples of leaf spot of annuals and perennials include:

Alternaria fungus leaf spot on impatiens, marigold, rudbeckia, sunflower, and zinnia.
Fungal leaf streak, sometimes confused with rust, occurs on daylily.
Reddish leaf petiole streaks on peony are symptoms of Cladosporium infections.
Rose black spot is the most common defoliating disease of roses.
Iris is subject to a fungal and a bacterial leaf spot, both of which produce a gray spot with yellow halo.
Bacterial and fungal leaf spots also affect English ivy.
Begonia, chrysanthemum, and zinnia are subject to bacterial leaf spot.
Geranium bacterial blight begins as a leaf spot.
Foliar nematodes, common on shade-grown plants, cause angular spots on brunnera and heuchera, irregular blotches on anemone and salvia, and wedge-shaped dead patches on hosta. Signs of foliar nematodes may be glimpsed in leaf water droplets with a good hand lens.

Powdery mildew.

Signs of the powdery mildew fungus can be seen first as small patches and spreading to cover leaves, petioles, flowers, and stems of infected plants. These signs consist of a whitish or grayish mat of fungal mycelium, conidiospores, and conidiophores which bear the spores. Infected leaves may be twisted, curled, and distorted while covered with fungal signs. In some cases, fungal signs are sparse and leaves develop reddish splotches or take on a yellowish cast. In the landscape, powdery mildew especially affects begonia, chrysanthemum, columbine, monarda, phlox, rhododendron, rose, sedum, and zinnia. Powdery mildew does not require periods of rain or dew to thrive; warm weather and high humidity favor the disease.

Downy mildew.

Yellow patches are often observed on the upper surface of leaves infected with downy mildew. On the leaf underside, the fungus produces a whitish or grayish fuzzy fungal growth consisting of sporangial stalks and sporangia, best seen in early morning while the leaves are still moist. On rose, symptoms include dark, angular spots which produce fungal signs on the leaf undersides. Infected leaves shrivel up and die. Downy mildew can be found on alyssum, ornamental tobacco, pansy, rose, salvia, and snapdragon.

Botrytis blight.

When Botrytis blight (gray mold) is active, flowers are often attacked and blighted flowers may have dead, tan spots or blotches, or turn completely brown. Botrytis also causes tan to brown leaf spots and shoot blights, especially during cloudy, cool, moist weather. When the disease is active, signs of disease appear on dead tissues as gray or tan moldy growth of the causal fungus. Under moist conditions, almost all annuals and perennials can be affected by gray mold.

Virus diseases.

Plant virus symptoms appear commonly on the foliage, but plants are typically systemically infected. Rose mosaic virus symptoms can be seen as patterns of yellow and light-green lines, splotches, or speckles on infected leaves. Yellow or brown ring spots can be one symptom of impatiens necrotic spot virus (INSV) on New Guinea impatiens. INSV and its close relative, tomato spotted wilt virus, can also cause malformed strap-shaped leaves and stunting. During recent years, unusual virus diseases of landscape perennials such as anemone, hosta, and peony have appeared in the U.K. Plant Disease Diagnostic Laboratory with symptoms of ring spots, chlorotic spots, and mottled leaves.

Adapted from "RECOGNIZING FOLIAR DISEASES OF LANDSCAPE ANNUALS AND PERENNIALS" By John Hartman in the February 6, 2006 edition of the Kentucky Pest News form the College of Agriculture, University of Kentucky.

Turf - Fungicides for Brown Patch Control

The following is information on Brown Patch disease in turf and the use of fungicides for the control of this disease.

Brown Patch (= Rhizoctonia Blight)
Pathogen: Rhizoctonia solani, Rhizoctonia zeae
Principal Turfgrass Hosts: Ryegrasses, tall fescue, and bentgrasses
Season: June-September

Comments: Most severe during warm, humid weather, especially when night temperatures exceed 60ºF. Avoid high nitrogen fertility during summer. Periodically aerify and use other practices that promote good soil drainage. Improve air circulation. The use of fans on putting greens with poor air circulation can reduce brown patch pressure dramatically by improving air circulation, reducing soil moisture, shortening periods of leaf wetness, and lowering canopy temperature. On putting greens, start a preventive spray program when low temperatures exceed 60ºF for two to three consecutive nights (usually early June in central Kentucky and late May in western Kentucky). During the period from early July through mid‑August, when disease pressure typically is highest, use products with good to excellent effectiveness against brown patch. A curative program (rather than a preventive program) during this time of year is discouraged because of the potential for rapid disease development and the low recuperative potential of creeping bentgrass at that time of year.

When curative control is required, consider using azoxystrobin or pyraclostrobin; expect that symptoms may increase for several days after application as previously infected tissues continue to develop symptoms. Applications of PCNB prior to or during hot weather may cause phytotoxicity to creeping bentgrass. Use insecticides and herbicides judiciously during an active outbreak of brown patch as several of these have been shown to increase brown patch activity. Various plant growth regulators (PGRs) used on turfgrasses have been shown to occasionally influence brown patch severity. In particular, applications of Cutless (flurprimidol) have been shown to reduce the efficacy of several DMI fungicides against brown patch. In a University of Kentucky test, Daconil Ultrex caused phytotoxicity on creeping bentgrass under acute drought stress. If using thiophanate-methyl, check the pH of the water used to prepare spray solutions; if the pH is high, include a buffering agent to bring the pH to 7.0 to avoid alkaline hydrolysis.

Click on Table for a Larger Image

Rating system for fungicide efficacy:4 = consistently good to excellent control in published experiments; 3 = good to excellent control in most experiments; 2 = fair to good control in most experiments; 1 = control is inconsistent between experiments but performs well in some instances; N = no efficacy; L = limited published data on effectiveness; + = intermediate between two efficacy categories.

From "Chemical Control of Turfgrass Diseases 2008" by Paul Vincelli, Department of Plant Pathology, and A. J. Powell, Department of Plant and Soil Sciences, University of Kentucky

Turf - Disarm Fungicide

The following is information on Disarm fungicide for use in Turf for disease control.

Disarm® 480 SC fungicide (containing the active ingredient fluoxastrobin) is a relatively new systemic QoI fungicide for turf disease control from Arysta Life Science. The QoI family of fungicides currently sold for turf disease control are chemically classified as strobilurin fungicides, and readers may know them by that name. This fungicide family includes Heritage® (azoxystrobin), Compass® (trifloxystrobin), and Insignia® (pyraclostrobin).

Diseases controlled

Disarm® is labeled for control of a wide variety of diseases. The symbol (*) indicates that the disease is common; (º) indicates the disease occurs but rarely warrants fungicide treatment.

Anthracnose (*)
Brown patch (*)
Cool-weather brown patch (=yellow patch) (*)
Fusarium patch (=Microdochium patch) (*)
Gray leaf spot (*)
Leaf spot caused by Bipolaris sorokiniana (*)
Melting Out caused by Drechslera poae (*)
Pink patch (º)
Pink snow mold (*)
Typhula blight (º)
Pythium blight (*)
Pythium root rot (*)
Red thread (*)
Southern blight (º)
Spring dead spot (*)
Summer patch (*)
Take-all patch (*)
Target spot (º)

Disarm has show to have good to excellent control of Brown Patch and Pythium Blight in University trials.

Resistance management

There are very specific use guidelines on the Disarm® label relating to reducing the risk of fungicide resistance. Resistance to QoI fungicides has been reported in gray leaf spot, anthracnose, and Pythium blight, and I don't think it is overly pessimistic to predict that other diseases will develop resistance with continued use of these fungicides. Therefore, it is important to pay close attention to the use restrictions on the Disarm® label as well as the labels of all QoI fungicides.

Any time you apply fungicide which is at-risk for the development of resistance, you run the risk that you are selecting resistant biotypes of the pathogen. You cannot prevent the development of resistance if you are using the chemical. All you can hope to do is reduce the risk that the resistance will develop. The label guidelines are based on sound biological principles and will help reduce that risk.

Adapted from the article "DISARM®, A NEW FUNGICIDE FOR TURF DISEASE CONTROL" By Paul Vincelli in the March 12, 2007 edition of the Kentucky Pest New from the College of Agriculture, University of Kentucky.

Greenhouse - INSV and TSWV Viruses

INSV and TSWV are two common viruses that attack greenhouse plants in Delaware. The following is an article on this subject.

Greenhouse growers are gearing up for production of bedding plants and perennials for spring sale. Production of these transplants may involve propagation of possibly infected overwintering stock or movement of plugs, transplants and sometimes plant diseases long distances. Diseases caused by impatiens necrotic spot virus and tomato spotted wilt virus are important causes of losses in greenhouse ornamentals. Although the virus and thrips (the disease vector) are common, growers can avoid crop losses by aggressively controlling thrips and the viruses it spreads. Impatiens Necrotic Spot Virus (INSV) and Tomato Spotted Wilt Virus (TSWV) are two different but closely related viruses causing similar symptoms.

The most common and dramatic problems of greenhouse ornamentals in Delaware have been due to INSV. This virus is usually the one causing disease symptoms on impatiens, New Guinea impatiens, begonias, petunias snapdragons, cyclamen, cineraria and gloxinia. Both viruses are transmitted from plant to plant by western flower thrips. An adult thrips can infect a plant with virus after feeding for only 30 minutes. TSWV is very damaging to tobacco, tomatoes, and peppers, but it also attacks some ornamentals, most often dahlias imported from overseas, and chrysanthemums and (rarely) ivy geraniums. Both viruses have a very wide host range and both are vectored by western flower thrips.

Virus Disease Symptoms. TSWV/INSV causes a wide variety of symptoms including wilting, stem death, stunting, yellowing, poor flowering; and sunken spots, etches, or ring spots on leaves. Symptoms are not very specific or consistent, and merely tell the grower that there is something wrong with the plant. Many other diseases and plant problems can cause symptoms that resemble TSWV/INSV. Virus symptoms may depend on time of year, type of plant, age of plant, plant physiological state, growing conditions at the time of infection, and strain of virus. In the UD Plant Disease Diagnostic Laboratory, positive diagnosis is made by testing infected plant tissue with an ELISA test based on a chemical reaction to the virus proteins. Separate tests are used to look for both TSWV and INSV because a plant may have either or both viruses.

Managing INSV and TSWV in greenhouse ornamentals.

Inspect incoming plant material for signs of thrips feeding injury, or for symptoms indicative of TSWV or INSV infection. Most plant materials coming from suppliers are not guaranteed to be disease free; thus your inspections are most important. Insist on good thrips control from your plant suppliers.

Isolate incoming plants from all other plants in the greenhouse until certain they are free of the viruses.

Separate cutting crops from seedlings. The disease frequently enters the greenhouse within vegetatively propagated plant material. Hanging baskets of infected cutting crops over seedlings can lead to bedding plant losses, since the young seedlings are highly susceptible.

Immediately discard plants showing distinctive TSWV/INSV symptoms. Early destruction of a few infected plants may prevent an epidemic through all the susceptible plants in the greenhouse. If in doubt, throw them out. Infected plants cannot be cured.

Do not vegetatively propagate infected plants. The virus can still be maintained in a crop through vegetative propagation even in the absence of western flower thrips.

Plants may act as reservoirs of the virus. Flowering pot plant crops such as cyclamen can serve to carry the disease over from the fall to the following bedding plant season, as might weeds left under the benches. Eliminate weeds in and near the greenhouse which may harbor thrips and/or the virus.

Consider using petunia plants as indicators to monitor for TSWV/INSV and thrips feeding injuries; 'Calypso', 'Super Blue Magic' or Summer Madness' petunias may all be used as indicators of TSWV/INSV. Use a yellow (NON-sticky) card to help attract the thrips to the petunias.

Losses have been greatest with gloxinia, double flowered impatiens, New Guinea impatiens, begonia and cyclamen crops. Be particularly careful to keep these crops isolated from potential sources of virus.

Be aware that vegetable and tobacco transplants are also susceptible to these viruses and can serve as reservoirs of infection.

Perennial plant growers need to aggressively attack TSWV and western flower thrips in both greenhouse and outdoor plantings, and must be aware that plants originating from greenhouse production but now planted outdoors may carry the virus. Even if the thrips do not overwinter in DE, vegetatively propagating infected plants will maintain and spread the virus. Garden center operators must also be aware of the biology of TSWV and western flower thrips, especially if they keep herbaceous plants all year. Many perennials are susceptible to the virus and attractive to thrips. An infected perennial will retain the virus until that plant dies.

Adapted from "INSV AND TSWV ARE THREATS TO GREENHOUSE ORNAMENTAL PRODUCTION" By John Hartman in the Feb 12, 2007 edition of the Kentucky Pest News from the College of Agriculture at the University of Kentucky.

Landscape - Black Gum, a Substitute for Norway Maple

Black gum is a good native tree that can be substituted for Norway maples that can be a problem invasive plant. The following are pictures of the fall color of Black Gum.

Pictures from Plants for a Liveable Delaware. Go to http://ag.udel.edu/extension/horticulture/pdf/PLD.pdf for the full publication.

Landscape - Alternatives to Norway Maples

Norway maples have been used extensively as shade trees but have a number of problems. The can be susceptible to wilt disease, they are difficult to plant turf under, and they have become invasive in natural areas. The following are some good substitutes for Norway maples.

Red maple (Acer rubrum) – 60’, dense rounded shade tree with excellent red fall color and tolerance to both wet and dry conditions (Native to DE)

European hornbeam (Carpinus betulus ‘Fastigiata’) – pyramidal to oval; 40-60’ tree with late, yellow fall color and tolerance of wet and dry conditions

Katsuratree (Cercidiphyllum japonicum) – 40-60’ with pyramidal to wide-spreading habit; leaves emerge reddish purple, change to bluish green in summer, and yellow in fall; may require water during drought periods

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

Sweet gum ( Liquidambar styraciflua) – 60’ pyramidal tree; purple, orange and yellow fall color on the same tree and tolerance of urban conditions (gumballs can be messy) (Native to DE)

Black gum (Nyssa sylvatica) – 30-50’ irregularly rounded tree with green glossy summer foliage and brilliant red foliage in fall; tolerates wet, dry and urban conditions (Native to DE)

Swamp white oak (Quercus bicolor) – 50-60’ rounded tree with yellow-bronze fall color and excellent drought tolerance as well as tolerance to wet and urban conditions (Native to DE)

Shingle oak (Quercus imbricaria) – 30-45’ conical tree; leaves unfold red in spring with lustrous dark green summer color and yellow-brown fall color; tolerates wet, dry and urban conditions (Native to Delaware)

Information from Plants for a Liveable Delaware. For full information, credits, and pictures go to http://ag.udel.edu/extension/horticulture/pdf/PLD.pdf

Greenhouse - Problems to Watch For when Receiving Plugs or Cuttings

Many of the problems that we have with diseases and insects in greenhouses start with infected or infested planting material that is received from suppliers. It is important to inspect all incoming shipments for diseases and insects and reject any that have problems. The following are some thoughts on this subject.

Be alert for: downy mildew on bacopa, coleus, impatiens, and argyranthemum; black root rot on vinca, calibrachoa, petunia, pansy, and others; INSV on Impatiens wallerana and New Guinea impatiens, lobelia, tuberous begonia and others. Cyclamen mites have been more common in recent seasons an infest many crops, especially New Guinea impatiens.

Detecting problems on arrival is key since suppliers will resolve problems if they believe they are at fault. Don’t expect suppliers to be as receptive if you report problems weeks later when your greenhouse could be the source. Additionally, identifying problems that may just involve a few flats will allow action to prevent spreading them throughout your whole operation via mixed combination planters or hanging baskets.

Modified from the February 2007 edition of Floriculture IPM Notes from Rutgers and Cornell Cooperative Extension.

Greenhouse - Dipping Plugs or Liners With Growth Regulators

Growth regulators are important tools for greenhouse growers to keep certain annuals compact. The following is an article on dipping liners, trays or pots with growth regulator before planting.

The practice of dipping plugs or liners into a solution of plant growth retardant (PGR) before transplant is increasingly being used by growers to control plant height of aggressive annuals. This technique is commonly referred to as a liner dip or liner soak, but it applies to seedling plugs as well. Liner dips are particularly useful if a grower is interested in regulating the initial growth of plants in mixed containers. Aggressive species can be treated with a liner dip before transplant, which can allow less aggressive, untreated plants to become established before aggressive plants take over.

In the past few years, the Floriculture Research Team at MSU has conducted experiments to identify suggested rates of chemicals containing uniconazole (the active ingredient in Sumagic and Concise) and paclobutrazol (the active ingredient in Piccolo, Bonzi and Paczol). We’ve placed liners in PGR solutions for approximately 30 seconds, and then transplanted the liners several hours later or the following day. Plants were grown until flowering, and then plant height data was collected. Additional studies have been performed at the University of Florida that provides additional useful information.

There are several factors to consider when choosing a liner dip concentration, including:
Chemical
Plant species
Magnitude of the desired response
Media moisture content
Growing conditions and location.

During spring conditions in Michigan, typical rates of paclobutrazol used as a liner dip on aggressive vegetative annuals range from 4 to 8 ppm, including crops such as petunia, scaevola, argyranthemum and calibrachoa, and 8 to 12 ppm for verbena. Lower rates are generally used for products containing uniconazole, such as 1 to 2 ppm for petunia, 2 to 4 ppm for calibrachoa, and 3 to 4 ppm for argyranthemum, scaevola and verbena. These rates generally provide a long-lasting response (six to eight weeks), and lower rates should be used if a shorter response period is desired. In locations with warmer, sunnier weather, higher rates may be needed to achieve the desired response.

Finally, the media moisture content can have a significant impact on the uptake of the liner dip solution, and thus the plant response. If the media is moist, not much PGR solution will be absorbed by the media, and thus a smaller response will be attained. Conversely, if the media is very dry, much more PGR solution will be absorbed, producing a stronger response. We suggest that growers ensure that the media of liners and plugs is slightly moist, and not wet or dry, at the time of application. This will ensure a more uniform response within the plug tray and from one application date to another.

As with all plant growth retardants, we strongly encourage growers to conduct their own trials on a small scale to determine the most appropriate rates for their crops and growing conditions.

From the March 1, 2007, Michigan State University Greenhouse Alert Newsletter "Tips on plant growth retardant liner dips" by Erik Runkle.

Greenhouse - Downy Mildew on Coleus (Plectranthus)

Downy Mildew is a disease that is becoming more prevalent in greenhouses. In particular, Coleus, now known as Plectranthus, can be infected. The following are some slides of this disease on Coleus. Click on slides for a larger image.

From a presentation by Bob Mulrooney, Extension Plant Pathologist, UD.

Greenhouse - Control of Major Greenhouse Pests

The follwing are some slides on the control of some of our major insect and mite pests in greenhouses. Click on the slides for a larger image.

From a presentation by Dr. Brian Kunkle, UD Extension Ornamental IPM specialist

Turf - Fluroxypyr Herbicide

Another new herbicide on the market for turf is fluroxypyr which is contained in Spotlight herbicide and Escalade 2 herbicide. The following slides have information about this herbicide.

Click on Slide for a larger image

From a presentation by Dr. Steve Hart, Rutgers University.

Landscape - Mites and Their Control

Mites are a common pest in landscapes. The following are some slides on mites and mite control

From a presentation by Casey Sclar, Ph.D. – Plant Health Care Division Leader, Longwood Gardens, Inc. Kennett Square, PA

Turf - Herbicide Products for Yellow Nutsedge Control

Yellow nutsedge can be a problem weed in turf. The following are some slides on newer nutsedge control products that are available for use in turf.

Click on Slides for a Larger Image

Slides from a presentation by Dr. Steve Hart, Rutgers University.

Landscape - Scale Insects and Conserving Beneficials

The following are some slides on scale insects and their control as well as how to conserve beneficial insect in the landscape.

From a presentation by Casey Sclar, Ph.D. – Plant Health Care Division Leader, Longwood Gardens, Inc. Kennett Square, PA