Inspector Findings in Kentucky

By Lee Townsend, Extension Entomologist

Galls are irregular plant growths which are stimulated by the reaction between plant hormones and powerful growth regulating chemicals produced by some insects or mites. Many species of gall makers attack oaks and most are caused by tiny wasps.

Galls may occur on leaves, branches, bark, flowers, buds, acorns, or roots. Leaf and twig galls are most noticeable. The inhabitant gains its nutrients from the inner gall tissue. Galls also provide some protection from natural enemies and insecticide sprays. Important details of the life cycles of many gall makers are not known so specific recommendations to time control measures most effectively are not available.

Gall makers must attack at a particular time in the year to be successful. Otherwise, they may not be able to stimulate the plant to produce the tissue which forms the gall. Generally, initiation of leaf galls occurs around "bud break" or as new leaves begin to unfold in the spring.

Once the symptom or gall appears, the causative arthropod is protected within the structure. This means that remedial actions, other than pruning in some cases, are not effective. Preventive action is necessary to attempt to reduce the infestation the following season and these may be of limited value.

Fortunately, most galls, especially those on leaves and leaf structures, do not harm the health of the tree.

By John Hartman, Extension Plant Pathologist

Dogwood leaf splotches, dead areas on the leaves, have resulted from infections by the gray mold fungus, Botrytis cinerea that occurred recently, just after the flower bracts fell. During wet weather, fading bracts often develop gray mold disease and fall to the ground unnoticed. Some diseased bracts, however fall on dogwood leaves and stick there while the infection spreads to the leaf itself. With the advent of dry weather the rotted flower bract shrivels up, leaving a dead blotch or spot on the leaf. These spots will not spread for the rest of the season unless we have a return of cool, wet weather. There has been some concern that these dead spots were symptoms of dogwood anthracnose.

Crabapple, apple, and hawthorn rust symptoms are becoming more visible. Infected, swollen fruit of hawthorn are more prominent than their healthy counterparts in the same fruit cluster. The typical orange spots on crabapple and apple leaves are now easily seen.

Pachysandra leaf blight and canker, caused by the fungus Volutella, is also widespread, but is sometimes confused with spring frost injury. Both problems cause death of leaf margins, but leaf blight shows concentric zones of infection within the dead tissue. In addition, where leaf blight disease occurs, dark brown, dead cankers are visible on the stems and stolons.

Peony red spot disease, caused by the fungus Cladosporium is becoming visible on peony stems. Look for short reddish-brown streaks all along the stems. Thorough sanitation in the fall is the best way to manage this disease.

Rose black spot disease control begins now if disease-susceptible roses such as hybrid tea, floribunda, and grandiflora roses are being grown. Shrub roses are less susceptible and may not require fungicide sprays.

Homeowners may use protectant fungicides such as Captan (captan), Carbamate (ferbam), Daconil 2787 or other chlorothalonil products, and Maneb (maneb). Systemic or locally systemic fungicides include Funginex (triforine) and Immunox or Kgrow multipurpose fungicide (myclobutanil).

Baking soda has been proposed as a fungicide for homeowners to prevent black spot, but under our conditions of high disease pressure, it may prove unreliable.

Professional applicators can use Banner Maxx (propiconazol), Eagle (myclobutanil), Fore (mancozeb), and Rubigan (fenarimol). Fenarimol, myclobutanil, propiconazol, and triforine should all be effective against rose powdery mildew and rust diseases as well.

By Mike Potter and Lee Townsend, Extension Entomologists

Bagworms are caterpillars that make distinctive spindle-shaped bags on a variety of trees and shrubs throughout Kentucky. They attack both deciduous trees and evergreens, but are especially damaging to juniper, arborvitae, spruce, pine and cedar. Large populations of bagworms can strip plants of their foliage and eventually cause them to die. Infestations often go unnoticed because people mistake the protective bags for pine cones or other plant structures.

Description and Habits

Bagworms are the larval (caterpillar) stage of a moth that is rarely seen. Only the males develop into typical moths capable of flight. The adult female is grub-like and remains inside the bag until just before she dies.

Bagworms pass the winter as eggs inside the bag that contained the previous year’s female. In mid to late May the eggs hatch, and the tiny larvae crawl out from the end of the bag in search of food. By using silk and bits of plant material, they soon construct a small bag around their hind part that looks like a tiny, upright ice cream cone. As the larvae continue to feed and grow, they enlarge the bag enabling them to withdraw into it when disturbed. Older larvae strip evergreens of their needles and consume whole leaves of susceptible deciduous species, leaving only the larger veins. The bag is ornamented with bits of whatever type of vegetation they are feeding upon.

By early fall, the bags reach their maximum size of 1-1/2 to 2 inches. At this time the larvae permanently suspend their bags (pointing downward) from twigs, and transform into the pupa or resting stage before becoming an adult.

Adults emerge from the pupal stage in early fall. Males are black, furry, clear-winged moths with about a 1-inch wing span. They are active fliers and fly in search of females which remain inside their bags. The females produce a powerful scent, or pheromone, that attracts the males. The creamy white females lack wings and legs and appear to be no more than grubs. The male flies to the female bag, inserts his abdomen in the hole in the bottom of the bag and mates with the female. After the fertilized female has laid several hundred eggs inside her old pupal case within the bag, she drops from the bag and dies. The eggs remain in the bag until the following May when the cycle begins again. There is one generation per year.

Bagworms have two means of dispersing from plant to plant. Very young larvae may spin strands of silk and be carried fairly long distances by wind. Larger larvae may move short distances by crawling.

Bagworm Control

If only a few small trees or shrubs are infested, picking the bags off by hand and disposing of them may afford satisfactory control. This approach is most effective during fall, winter or early spring before the eggs have hatched.

When many small bagworms are infesting evergreens, an insecticide may be needed to prevent serious damage. The best time to apply an insecticide is while the larvae are still small (less than 1/2-inch long). In Kentucky, this is usually in June. Small larvae are more vulnerable to insecticides, and inflict less damage. Carefully inspect susceptible landscape plants, especially evergreens, for last year’s bags. Young bagworms are harder to see; look closely for the small, upright bags which have the appearance of tiny ice cream cones constructed of bits of plant material. Preventive treatment is often justified on plants that were heavily infested with bagworms the previous year.

Several products are available for homeowner and professional use. For homeowners, conventional insecticides such as Sevin, Dursban, diazinon, and malathion, or the microbial insecticide Bacillus thuringiensis (BT) provide satisfactory results. The BT products have very low mammalian toxicities, but are only effective against younger larvae. If large bagworms are present (more than about 3/4-inch long), a conventional insecticide probably will provide better results. For nursery and landscape professionals, other effective products include Astro, Decathlon, Ficam, Mavrik, Orthene, Pounce, Scimitar, Talstar and Tempo. Foliage should be thoroughly wetted with the insecticide spray in order to achieve thorough coverage.

Beginning the first week of June, gypsy moth traps will again be set out to detect the movement of gypsy moths. This year trapping will concentrate around eastern and north central Kentucky. Louisville and Lexington will also be included in the trapping area. A total of 65 counties will be trapped. Since there were a relatively high number of gypsy moths caught in Boyd (11 moths) and Greenup (21 moths) counties, production nurseries in those counties will have a trap placed in their fields to ensure that they are gypsy moth free.

by John Hartman, Monte Johnson and Ric Bessin

Diseases caused by tomato spotted wilt virus (TSWV) and impatiens necrotic spot virus (INSV) have caused losses in Kentucky greenhouse crops. Although the virus is easily acquired and thrips (the disease vector) are common, growers who aggressively attack the problem can avoid crop losses by controlling thrips and the viruses they spread.

There are two different but closely related viruses causing greenhouse crop symptoms. The most common and dramatic problems of greenhouse ornamentals in Kentucky have been due to INSV, previously known as TSWV-I. This virus is usually the one causing problems on impatiens, New Guinea impatiens, begonias, snapdragons, cyclamen, cineraria and gloxinia. INSV can infect tobacco seedlings but does very little damage, because this virus apparently does not become systemic in most tobaccos. 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. Known in the past as TSWV-L, 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. Both are vectored by western flower thrips.

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.

Positive diagnosis is made by submitting a plant to a plant disease clinic that uses either inoculation of special indicator plants or chemical tests to determine if the virus is present. In the U.K. Plant Disease Diagnostic Laboratory, separate tests are run to look for both TSWV and INSV. A plant may have either or both viruses.

*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.

*Be especially careful when producing vegetable transplants; tomato and pepper, in particular, may be severely affected by TSWV/INSV. The disease may cause subsequent death or yield losses in the field. Be careful of TSWV when producing tobacco transplants.

*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.

Adult western flower thrips are less than two mm long. Males are pale yellow and females are two-toned, with a yellow to orange-brown head and thorax, with a brown abdomen. Thrips lay their eggs inside the plant tissue (where the eggs are protected from insecticides) until they hatch and emerge 2 to 4 days later. The stage instar larva is clear. The second stage larva is yellow at first. Both the first and second larval stage hide among the bud and flower parts of the plant. The second stage larva turns white just before it molts and moves to the soil or leaf litter where it enters the pupal stage and undergoes metamorphosis to an adult. Adults emerge from the soil 2 to 5 days later and may be yellow or dark brown. They hold their four hair-fringed wings flat over their backs. Adults can live 30 to 45 days.

Thrips feed by piercing plant cells with their mouthparts and sucking out the cellular contents. The damage to plant cells caused by thrips feeding can result in deformation of flowers, leaves and shoots. There is often silvery streaking and flecking on expanded leaves. Thrips often deposit tiny greenish-black fecal specks on leaves when they feed.

Thrips management involves early detection and identification of the insect, followed by a vigorous control program.

Detection of thrips activity:

*Inspect all incoming plants for thrips. Tap the plant with a pencil while holding a sheet of white paper to catch any falling insects. Check white and yellow flowers with a hand lens. Remove and destroy heavily infested flowers.

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

*Use traps to monitor presence of thrips in the greenhouse. Since thrips are very small and stay hidden most of the time, they are difficult to detect. Yellow or blue sticky cards (available from most greenhouse supply companies) placed at or just above crop height are excellent for monitoring thrips. Blue is effective for thrips but is not a good all around color for other insects. One to three cards per 1,000 sq ft is recommended. Trapping efficiency depends on the number used per square foot and placement rather than the size of the card. Place some near vents, doors, and other openings. Change the cards once a week. Wrap each card in one layer of cellophane for ease of handling. If you are uncertain of the identity of the insects you have trapped, contact your county extension agent for assistance. Record the number of thrips trapped to determine if the population is increasing or decreasing. Count and change cards weekly, noting upward population trends that signal the need for treatment. More than 10 western flower thrips per card per week is a threshold value some growers have found useful. A hand lens will be needed to recognize the thrips on the traps.

*Understand thrips biology (see above).

*Use available chemical controls. A single application of an insecticide is not adequate. Applications are made at 5-day intervals unless otherwise stated on the insecticide label.

*Use one insecticide for one generation of thrips. That means, apply one insecticide two to three times over 14 to 15 days. The first insecticide application kills winged adults while the second and third kills newly emerged wingless individuals. Then switch to a different class of insecticide.

*Rotate insecticides between chemical classes every 3-4 weeks to discourage the development of pesticide resistance in the thrips population. Do not use tank mixes of different materials since this tends to foster the development of insecticide resistance in thrips.

*Thorough coverage is required. Alternate between fogging and spraying methods of application to achieve good coverage.

*Be certain the insecticide is registered for use in the greenhouse and that the names of the plants to be treated are on the chemical label. Pyrethroids are said to agitate the thrips and get them to move out where they are exposed to other pesticides. However, agitated thrips may move from plant to plant more than normal and could, theoretically, lead to greater spread of the virus if not killed quickly.

*Predatory insects (biological control) for release into the greenhouse are under development.

*Maintain strict thrips control on all plants kept in the greenhouse.

*Eliminate all weeds and all plants not being carefully tended from inside the greenhouse. Such plants may harbor both the thrips and the virus.

*Consider screening the vents where western flower thrips may be entering from outside (fall and spring, especially). Microscreening (100-1000 holes per sq in) reduces air flow, so vent area must be increased by 4 or 5 times.

*Westem flower thrips are not known to survive the winter outdoors in Kentucky.

TSWV and thrips may follow the crop out of the greenhouse.

Nurserymen, garden center operators, and others serving the plant industry need to understand how the virus/thrips problems arise in the greenhouse. Plants are purchased from many different sources and shipped from greenhouse to greenhouse. If the supplier of the original plants has a problem with a disease, insect, or mite, it should not be surprising that those problems accompany the plants they sell.

Thrips problems can develop very rapidly, even where an operation may have never had thrips. From one infested plant, western flower thrips can suddenly be found on almost any green plant in the house. With the thrips-infested plants comes the virus. The rapidly spreading thrips carry the virus from plant to plant.

Although plants produced outdoors may not be subject to such explosive and dramatic outbreaks because of a less favorable environment and the presence of natural biological controls, it is always possible to introduce a new pathogen or insect into the outdoor production area when purchasing and planting new material.

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 Kentucky, 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 thrips. An infected perennial will retain the virus until that plant dies.

by Lee Townsend, Extension Entomologist

Cottony Maple scale occurs on the twigs and leaves of a wide variety of woody plants, but most often on maples. The insect is flat, oval, brown, and about 1/8" long. The large, white, cottony egg sac protruding from under the body, and its copious production of honeydew makes this scale very noticeable. There is one generation each year. Crawlers are active in mid June.

In general, controls will be more effective if the scale population on a plant is first physically reduced by pruning out heavily infested and sickly branches. In some cases, large sized scales can be scrubbed off with a stiff brush. Horticultural oil sprays kill primarily by smothering, so they will be less effective against scales crowded together or occurring in layers the plant. Insecticidal soaps provide a new alternative. They are very effective against both active and settled crawlers. Oils and soaps are safe to use and are especially good choices for sensitive areas, such as where people are present soon after treatment. Because of their short residual, they help to conserve beneficial species.

Horticultural spray oils kill all stages of scales that are present at the time of application, and often give good control. Most trees and shrubs can tolerate application of light (summer oil) even during the summer months. Refer to the product label for guidelines on plant sensitivity and any temperature restrictions. Oil products labeled as summer, superior or Volck oil are of the highest grade and may be used on tolerant plants during either the growing season or the dormant season, but at different spray concentrations.

An alternative to oil sprays are contact insecticides applied during the growing season when the crawler stages of the scales are present. The presence of crawlers can sometimes be determined by sharply tapping an infested twig or branch over a white paper. Crawlers are often orange, brown or purple and appear as moving specks of dust. Because of their waxy protective covering, other stages of scales are not readily controlled by contact insecticides. Contact insecticide sprays will not reach crawlers that have settled under old scales.

Insecticides registered for scale crawler control on outdoor plants include: Cygon (dimethoate), Dursban (chlorpyrifos), Diazinon, Malathion, Orthene (acephate) and Sevin (carbaryl). Although resistance to insecticides may occur in some cases, failure of contact sprays is more often the result of not timing the applications to coincide with crawler activity. Even when sprays are timed for optimum effect, complete control may not be achieved by single applications if crawler activity is spread over an extended period of time, or if populations are heavy and crawlers are under old scale shells. Thorough spray coverage is essential for good control.

By Lee Townsend, Extension Entomologist

Several specimens of calico scale have come into the insect ID lab this spring. These colorful, globular scales (about 1/4" in diameter) are dark brown with splotches of white. They can be found on all stone fruits and their ornamental cultivars. Flip over a scale now and you will see hundreds of small eggs. These will hatch soon and the tiny crawlers will move off to settle and feed on leaves during the summer. They will move back to twigs just before leaf drop in the fall.

Calico scales produce a large amount of liquid waste, called "honey dew". This liquid will fall onto leaves and branches and support the growth of sooty mold. The mold growth can be intense enough to interfere with photosynthesis.

By Mike Potter, Extension Entomologist

Four serious pests of landscape trees dogwood borer, bronze birch borer, flatheaded apple tree borer, and honey locust borer have emerged. The dogwood borer is the most serious pest of ornamental dogwoods, especially stressed trees in full sun. The bronze birch borer is a severe pest of white or paper birch, especially cultivated trees under stress. Flatheaded apple tree borers are major pests of red maples, hawthorns, flowering crabapple, and several other hardwoods, especially those which are newly transplanted or under stress.

Honey locust borers are serious pests of transplanted and established urban trees with limited root zones. Mated females of all four species fly to host trees and lay eggs on the bark.

Management Borers rarely injure healthy trees or shrubs growing in their natural environments. When transplanted into landscape settings, every effort should be made to minimize plant stresses such as drought, soil compaction, sun scald, soil compaction, lawn mower/weed trimmer injuries, etc. Because newly planted are under considerable stress, preventive sprays are advisable during the first couple of growing seasons after planting.

Timing is crucial in order to have a lethal residue of insecticide on the bark to intercept newly-hatched larvae before they burrow into the tree. Now is the appropriate time to apply protectant sprays for all four species. Lindane or Dursban are effective, and should be sprayed to runoff on the trunk and main scaffold limbs. A second application, three weeks after the first one, provides extended protection.