Dr. Kenneth W. Seebold, Jr. joined the Plant Pathology Department March 21, replacing Dr. William Nesmith, who retired last December. Dr. Seebold is a native Kentuckian, born in Louisville. Growing up in and around Louisville and spending a few semesters at the University of Louisville, Dr. Seebold felt the urge to move and explore new territories. He first ventured to Alabama where he was awarded a B.S. in Integrated Pest Management (1990) and a M.S. in Plant Pathology (1994), both from Auburn University. For his Master's research, Dr. Seebold studied the management of soilborne peanut diseases and the influence on biological control agents of improved fungicide applications. From Auburn, he headed further south, to Gainesville, gaining his Ph.D. in Plant Pathology from the University of Florida in 1998. His doctoral dissertation considered the influence of silicon fertilization on the development and control of blast disease in upland rice. Upon graduation, Dr. Seebold took a position in industry as Fungicide Project Leader for Uniroyal, in Bethany, Connecticut. There, he managed the testing of potential chemical and biological fungicides in the field. After two years with Uniroyal, Dr. Seebold accepted the position of Assistant Professor at the University of Georgia's Coastal Plain Experiment Station in Tifton. His research programs concerned the ecology, epidemiology, and control of soilborne and foliar fungal diseases of cotton and vegetables; in the latter case, particularly diseases of cucurbits and onion. Although primarily an applied researcher, Dr. Seebold interacted with various growers finding, through these interactions, that his calling lay in Extension. Dr. Seebold was anxious to return to his Kentucky roots, and brings both breadth and depth of expertise to his new position at the University of Kentucky. Dr. Seebold is an outgoing individual, well suited by professional background and personality to assume his Extension and applied research duties on behalf of the Commonwealth's tobacco and vegetable growers.
Two threatening plant diseases-Asian soybean rust and plum pox virus-were removed from the federal list of Select Agents last week. "Select Agents" are exotic disease-causing organisms that were considered in the 2002 Agricultural Bioterrorism Act to be significant threats for bioterrorism to crop or livestock production in the U.S. Select Agents are required to be handled in research laboratories only after registration and under strict conditions of biocontainment/biosafety and security. Deliberate introduction of Select Agents (bioterrorism threats) into the environment is a violation of federal law.
Phakopsora pachyrhizi, the cause of Asian soybean rust, was introduced last year into the continental U.S. through natural means, most likely on winds associated with Hurricane Ivan last September. The fungus appears to have overwintered in Florida. Since rust fungi like this one are readily spread in the wind, it is expected to continue to spread naturally in the U.S.
Plum pox potyvirus causes disease of stone fruits, reducing yield and marketability of the crop. According to a USDA news release last week, "Plum pox has been removed from the list of select agents and toxins because it does not spread easily by natural means and it would be difficult to spread intentionally."
Removal of these agents from the list of Select Agents does not negate the potential economic importance of these diseases. In particular, there is great concern about the potential destructive capability of Asian soybean rust in the Kentucky soybean crop, should environmental conditions favor early introduction and rapid disease development. For more information on Asian soybean rust, see the Kentucky Soybean rust web page.
All private applicators, noncommercial applicators, pesticide operators, and pesticide applicators who apply pesticides (General or Restricted Use) are required to maintain records of applications. The records must be kept for three (3) years from the date of use or application and made available for inspection to appropriate healthcare and regulatory people.
Specific information must be recorded for each application. There is no official form for these records but a model form is available from the Ky Department of Ag web page.
TERMITE SWARMERS can begin to fly most any time now (604, 605, 639, 640, 642); EASTERN TENT CATERPILLAR (424) egg hatch has started; REDBANDED LEAFROLLER (216) flight begins soon, CLOVER MITES (627) can begin to crawl LONE STAR TICKS (618) are out.
One of the most troublesome weed problems in Kentucky pastures and hayfields are thistles. Thistle plants can interfere with livestock grazing and limit the amount of available forage. The spring and early summer months is when thistles become a major problem for land owners and livestock producers who graze cattle or produce hay.
Musk thistle, also called nodding thistle, is the most common type of thistle plant found in Kentucky. The leaf surface of musk thistle is waxy in appearance and contains spines along the leaf margins. It is considered a noxious weed because of its ability to reproduce rapidly and limit pasture production. Musk thistle only reproduces by seed. Therefore, the major aspect of any control efforts is to prevent or limit new seed production.
Seed typically germinate in the fall and young thistle plants form a rosette which grows close to the ground during the winter months. Thistle rosettes often grow unnoticed until the rosettes begin to expand in diameter and flower stalks begin to elongate in the spring. The most active vegetative growth period of the plant is in the spring throughout the early summer months. Flower stalks emerge from the rosettes and are followed by bright purple to reddish flowers, which bloom in late May to early June. New seed develop within the flower heads and at maturity seed are easily carried by the wind and spread to other areas.
The most important step in a long-term control program for musk thistle is to prevent flowering, and the production and spread of new thistle seed. This can be accomplished by using various mechanical, biological, or chemical control methods.
Mechanical control consists of mowing, clipping pastures, or even hand-grubbing individual plants. These control methods should be initiated before flowers begin to open. Some regrowth and production of flowers can occur after mowing, but seed production will be notably less than if a timely mechanical control method had not been used. Thistle plants mowed or removed by hand after flowers have bloomed contain enough energy reserves that these plants will still produce viable seed.
A reduction in musk thistle populations can also be obtained through biological control methods. Two different insects are known to inhibit thistle growth and development, the thistle-head weevil and the thistle rosette weevil. The Thistle-Head Weevil can be found during the spring in many counties throughout central Kentucky. These insects feed on the maturing seed inside the developing flower head. The impact of the Thistle-Head Weevil will not eliminate all seed production, but can significantly reduce the amount of seed produced by individual plants in areas where the insect has become established.
Broadleaf herbicides labeled for use in pastures can be applied in grass pastures and non-cropland areas for control of musk thistle rosettes. For herbicides to be effective, however, the timing of the application is critical. Best results can be obtained if herbicides are applied to thistle plants that are in the early rosette stage of growth and actively growing. Therefore, the best times for herbicide application are in the early spring (during March and April when plants are actively growing) or in the fall (October or early November following new seed germination). When plants are in the rosette stage they are more susceptible to herbicide applications.
Herbicides which can be used in grass pastures include 2,4-D, Banvel, Weedmaster, Crossbow, and Pasturegard. For spring herbicide applications apply when air temperatures are above 55 F for 2 to 3 days. Complete spray coverage of the plant is also important. When herbicides are applied after flower stalks elongate, control will be less effective and inconsistent. When using herbicides for control consult the waiting period on the product label for livestock grazing restrictions following a herbicide application. Herbicides may not be a desirable control method in fields interseeded with clover, since clover is likely to be killed or severely injured. Furthermore, avoid spraying near crops such as tobacco, vegetables, or ornamental plantings. Also, avoid spray drift by not spraying on windy days or days with extremely high temperature and high humidity.
Very wet media and algal growth are major factors that contribute to problems with fungus gnats and shore flies in greenhouses and float systems. Adults are the noticeable stage but the larval stages of the shore fly can damage small plants in the cells, producing holes in the leaves that resemble the feeding of slugs and small cutworms.
The presence of these insects is usually overlooked until there is a massive swarm of adults sitting on the plant leaves. Orthene, or other acephate sprays, will kill adults and eventually may reduce their numbers but probably won't eliminate the problem. It is difficult to control the larval stages because they are down in the algae or under the protective cover of the leaves. Preventive control is based on keeping media from getting too wet and eliminating as many standing ground puddles as possible. Fungus gnats normally occur in low wet areas.
Occasionally, fungus gnat larvae can be serious pests in greenhouses. Most are scavengers, feeding on decaying organic matter in the growing media. However, some species will feed on root hairs, enter the roots, or even attack the crown or stem of the plant. Infested plants generally lack vigor and may begin to wilt. Adults (gnats) can be seen running on the foliage before injury caused by the larvae becomes apparent.
Fungus gnats are small (1/8") black flies with comparatively long legs and antennae, tiny heads, and one pair of clear wings. Females lay tiny ribbons of tiny yellowish white eggs in the growing media that hatch within 4 days. The clear larvae are legless and have black heads. Larvae feed for about 14 days and pupate near the surface of the medium. Adults live only about a week. Under greenhouse conditions, about 20-25 days are required to complete a generation.
Shore flies also are small gnats but have short antennae, red eyes, and heavier, darker bodies. A pair of smoky wings with several clear spots can be seen when looking closely at the insect. They are good fliers and can be seen resting on most any surface in the greenhouse. They resemble winged aphids but aphids have two pairs of wings and the distinctive, tube-like cornicles on the abdomen, and do not move as quickly.
The life cycle is similar to that of the fungus gnat. The yellow to brown larvae, which may be up to 1/4" long, differ in having no apparent head. Both larvae and adults feed mostly on algae growing on media, floors, benches, or pots. Some have been seen boring directly into the base of small plants. Damaged plants will easily break off at the soil surface. The adults may spread soil pathogens inside the greenhouse.
With the Spring Equinox upon us, buds are swelling and leaves will soon begin to emerge on landscape trees and shrubs. These few weeks before leaf emergence provide a good opportunity 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 in Kentucky include:In Kentucky, 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.
Scale insects are insidious sap feeding pests of shade trees and woody ornamentals that can significantly reduce plant health and vigor. While some are large conspicuous bumps, many are brown to gray and blend in with the bark. The gradual onset of subtle symptoms makes early detection of infestations difficult. Once plants become moderately to heavily infested, plants can show delayed bud break, reduced new growth, or signs of drought stress. In some cases, foliage and shoots may be stunted, faded, or discolored, and leaves often drop prematurely. If you see these signs and suspect scales, look for unusual bumps. Scales can easily be flipped over or scraped off with a fingernail.
Scale insects can be divided into two major groups, soft and hard (or armored), based on the nature of the waxy coverings they secrete. Soft scales have thin, waxy outer coverings that may be smooth or even cottony. For some, the summer portion of their life cycle is spent on leaves, while an over-wintering stage moves to twigs or branches before leaf drop. Many soft scales produce large volumes of a sugary waste liquid called "honeydew". Honeydew deposits give leaves an unnaturally shiny appearance and may attract large numbers of flies, ants, wasps, and other insects. Sooty mold fungus can grow on these deposits, causing leaves and branches to turn black.
In contrast, armored scales are covered with shed exoskeletons and layers of waxy secretions that provide relatively hard, shell-like covers which usually are round or elongate. Most armored scales remain on twigs or branches for their entire life and do not produce honeydew
Scale control can be challenging and may need to be repeated over several seasons. This is due in part to the protection from contact insecticides provided by the waxy coverings over immobile, mature scales. Also, proper timing of insecticide applications targeted to control the vulnerable crawler stage is a major key to success. Crawlers are very susceptible to control measures as they move over plant surfaces to find a feeding spot. Once settled on the plant, they begin to secrete a covering and are protected by it. Crawler activity varies by species so scale identification is an important part of a management program.
Periods of crawler activity are known for many of the common species. However, this may be hard to do if the life cycle of the scale is not known, or if crawlers are active at several times during the season. Electrical tape, sticky side out, can be placed on infested twigs, or infested leaves can be placed in clear plastic bags to capture crawlers and determine treatment timing.
ALTERNATIVES FOR CRAWLER CONTROL
Cultural control
Scales tend to thrive on stressed plants. Follow a recommended fertility program and watering regime to promote plant health. Keep in mind that over-fertilization favors buildups of scale on plants. If practical, improve plant sites to reduce stress and promote growth. Prune out heavily infested branches, if possible.
Insecticidal Sprays
Horticultural oils kill by suffocation or after penetrating over-wintering stages of the insect. Dormant oils are typically applied during February or March. They tend to be more effective against soft scales than the hard or armored species. Highly refined supreme, superior, or summer oils can be used on many trees and shrubs during the growing season. Read the product label for guidelines on plant sensitivity and temperature restriction before buying and using these products.
Insecticidal soaps are long chain fatty acids that kill susceptible insects through direct contact. Like horticultural oils, they require thorough coverage. Soaps leave no residue so repeated applications may be needed for some pests. These products may burn the foliage of sensitive plants so check the label for information about the plant species that you intend to treat.
A variety of natural and synthetic insecticides are labeled for use as sprays to control scale crawlers on landscape trees and shrubs. While the residual life of these products is generally longer than oils and soaps, timing, coverage, and precautions on damage to some plant species are very similar to those for oils and soaps. Representative products are listed in the table below.
Selected insecticides labeled for control of scale crawlers on trees and shrubs Insecticide common name followed by example brand names
*All insecticides have unique common names that can be found on just below the brand name on the product label. You may be able to find other brand name products for scale control that contain these active ingredients. Be sure that the product you select is labeled for the plants that you intend to spray.
The systemic insecticide imidacloprid (Bayer Advanced Garden Tree & Shrub Insect Control Concentrate) is applied as a drench around the root zone of infested plants. This water soluble insecticide is taken up by the roots and transported throughout the plant where it is ingested by sap feeding insects. It provides a means of scale control without reliance on sprays. This product may need to be applied in advance of crawler activity.
Evaluating Control
The success or failure of control efforts may not be readily apparent but here are some things to check. ? Dead soft scales often fall off of the plant, while dead armored scales remain in place. Live scales should produce a liquid when mashed, dead scales will be dry and not "bleed" when crushed. ? New foliage of infested plants should have a healthier appearance once the scale burden has been removed. Buds should break a little earlier than when the plant was infested and expanded leaves should have normal color and turgor. ? Sooty mold and shiny leaves should gradually disappear from plants that were infested with soft scales.
Natural Enemies
Scale insects can be attacked by a variety of lady beetles, predatory mites, and small parasitic wasps. Lady beetle adults and larvae can be seen but mites and parasitic wasps are very difficult to see. You can conserve natural enemies by using insecticidal soaps and oils which have limited impact on beneficial species in comparison to other control alternatives.
NOTE: Trade names are used to simplify the information presented in this newsletter. No endorsement by the Cooperative Extension Service is intended, nor is criticism implied of similar products that are not named.
Lee Townsend
Extension Entomologist