Inspector Findings in Kentucky

You should have received your nursery license renewal form in the mail last month. Many of you have already returned the application and we thank you for your quick reply. For those of you who have not yet paid, please do so as soon as possible.

The rosette weevil, Trichosirocalus horridus (Coleoptera: Curculionidae), a second natural enemy of musk thistle, was introduced from Italy to Virginia in 1974. Adult rosette weevils are oval, brown, and 1/8 inch long. They are identified by small tubercles behind the head and erect white and black hairs on the wing covers. Adults feed on leaf tissue, mate, and lay eggs in feeding grooves along the leaf midrib of musk thistle on warm days from March to November. Emerging larvae feed on the thistle by boring into the crown of the plant. Newly emerged adults feed on leaf tissue for 2 to 3 weeks before hibernating in debris on the soil. Adult and larval feeding on musk thistle causes the tissue to die around feeding sites, which may eventually kill the plant. This weevil produces one generation per year, overwintering as adults or as larvae in the rosette. Because T. horridus attacks the rosette stage of the musk thistle, its feeding complements the control by R. conicus, which feeds on developing flowers.

Unlike the musk thistle weevil, the rosette weevil has not been extensively released, and as a result is not yet widely distributed. Only Missouri has reported established populations of the rosette weevil in the North Central region. The weevil was first established in Webster County, Missouri in 1983 from weevils collected in Virginia. It has naturally spread to 19 additional counties since that time. The rosette weevil has also been successfully recolonized in three additional central Missouri counties and one northwest county.

Note: In early June, the department released approximately 2,000 rosette weevils at 3 sites within central Kentucky. The weevils came from the Missouri Department of Agriculture which collected the weevils from various sites within their state where the weevil is abundant.

By John Hartman, Extension Plant Pathologist

Mulches are used in Kentucky gardens and landscapes for many reasons. By suppressing vegetation near trees and shrubs, they keep mowers and string trimmers from damaging the bark. In landscape beds and in the garden, they control weeds, improve drainage, prevent soil water loss, lower soil temperatures, prevent soil erosion and, as they decompose they release minerals and leave behind humus which benefits the plants. Organic mulches generally suppress plant pathogenic fungi and enhance beneficial mycorrizal fungi. For continuing benefits, mulches need to be reapplied periodically.

Based on recent calls and inquiries, there seems to be a concern about nuisance fungi growing from mulch applied to landscape plants. There are many examples of fungi that grow on or from landscape mulch. Examples include stinkhorns (Mutinus and other related species), bird's nest fungus (Crucibularium), earth stars (Geastrum spp), assorted toadstools, slime molds (Physarum and other species), and the shotgun, or artillery fungus (Sphaerobolus). Of these, only the shotgun fungus is truly a nuisance because it shoots tiny black spore masses onto nearby surfaces such as home siding and cars. Fungi also permeate thick layers of dry mulch, creating a hydrophobic mulch which is not easily penetrated by water, thus causing irrigation problems. Fertility problems can result when the fungi decomposing mulch remove from the soil, nitrogen needed by the plants.

Can mulches transmit plant diseases? The fungi that cause Verticillium wilt and Phytophthora root rot can be carried in fresh mulch, but would not be a problem in composted mulch. Similarly, although the Rhizoctonia root rot fungus can use mulch as a food base before causing damping-off of seedling plants, it can be destroyed by six weeks of composting where mulch reaches 130-160 degrees F.

Most organic mulches do not contain plant pathogens. Beneficial mycorrhizal fungi are active in shallow (1-2") layers of mulch, but are inhibited by deep mulch layers (4-6").

With proper manipulation, mulches can be prevented from developing nuisance fungi while maintaining the benefits of mulch. Much work on microbes and mulch has been done in the laboratory of Dr. Harry Hoitink at Ohio State University. They have found that hardwood bark mulches (most commonly used in Kentucky), especially if finely ground, contain a large amount of cellulose which decomposes fairly rapidly and leads to nuisance fungi. Such mulches, if composted for a few weeks with added nitrogen, and maintained at moisture levels over 40% will not develop nuisance fungi. Such moisture levels allow bacteria and other fungi to compete with the nuisance molds. Moisture contents of organic products up to 50% will not present excessive transport weight problems.

The following are suggestions for the landscape industry and for homeowners wishing to avoid nuisance fungi:

- Purchase composted mulch products.

- Use mulches low in wood and high in bark.

- Avoid finely ground woody products unless composted first.

- If using fresh wood chips such as those from a tree maintenance firm, add water to the mulch and allow the pile to partially compost for six weeks. If the wood chips do not include fresh leaves, add some nitrogen to speed composting.

- Use coarse mulches, but do not apply them too deep.

- Soak all mulches with water immediately after application to enhance bacterial colonization.

- Do not apply mulch deeper than two inches.

- Do not use sour mulches (highly acidic mulches giving off an acrid odor) because they injure plants.

From Johnson & Lyon, Insects that Feed on Trees and Shrubs

The jumping oak gall, caused by the gall wasp Neuroterus saltatorius Hy. Edwards, is a tiny globular seedlike gall on the underside of oak leaves. The galls, each of which contains a single larva, drop to the ground when they have matured. The activity of the insect inside actually makes the gall jump repeatedly a few centimeters off the ground. The reason for this movement is not entirely clear, but it has been suggested that those individuals that succeed in locating themselves in a crevice in the soil are more likely to overwinter successfully than those that do not. These galls found on oaks in the West may at times become so numerous that they cause serious discoloration or premature loss of leaves.

After overwintering, a population of female N. saltatorius wasps emerges from the galls. Eggs are then laid in the newly opening buds. A few weeks later blisterlike swellings appear on the young white oak leaves. Wasps that emerge from these blisterlike galls are both males and females. After mating, females lay their eggs in the leaves and galls appear about 40 days later.

The question sometimes arises about why certain oaks bear large numbers of galls while adjacent trees of the same species have very few. In studies on N. saltatorius and a few other gall wasps, it was found that trees whose buds opened earlier than those on nearby trees were much more heavily galled. Trees without opening buds afford the wasps no opportunity to deposit their eggs. Gall makers must attack the plant at a very precise phenological moment if normal plant tissue is to be successfully stimulated to form a gall.

By John Hartman, Extension Plant Pathologist

For some areas of the state, the early June rainfall is apparently a welcome relief to otherwise dry spring weather. County Extension Agents, homeowners, and landscape maintenance workers are observing scorching symptoms on woody plants in some Kentucky locations. Trees that once were apparently healthy have leaves with interveinal and leaf tip necrosis typical of foliage water shortage. The species most often affected is sugar maple, but other trees such as dogwood, Japanese maple, and burning bush are also suffering. Although it is rare to see drought damage symptoms this early in the season, there may be good reasons why drought damage is appearing now in some locations.

For Kentucky, although January precipitation was above normal, February, March, April, and May precipitation has been below normal, especially in the Bluegrass region, according to data from the U.K. Agricultural Weather Center. It is the lack of rainfall in May that has brought on drought symptoms for sensitive plants. While May normally brings 4-5 inches of rain to most locations, all sites where data are being taken were short for the month. The shortage was quite variable, and sites such as Berea, Bowling Green, Campbellsville, Cumberland Gap, Dix Dam, Glasgow, Hardinsburg, Louisville, Mayfield, Paducah, Princeton, and Somerset received over 3 inches of rain in May, which should have been adequate for most landscape plants. On the other hand, sites such as Covington, Lexington, Spindletop, and Williamstown received less than 2 inches of rain; the latter three sites received not much more than 1 inch. Thus, it is along this I-75 corridor that drought symptoms are appearing, especially in the bluegrass region.

Trees with shallow root systems are most likely to undergo drought damage. Many landscape trees experienced saturated soil conditions last year from May until the middle of July. During this time, deeper roots may have been lost to flooding while roots near the soil surface were most likely to survive. This spring, in locations lacking rain, the shallow roots left from last year have not been sufficient to support the water needs of the trees. In other cases, trees growing in locations where bedrock is close to the surface and soils are shallow, the lack of rain has simply desiccated these sites. In still other circumstances, trees recently transplanted just simply have not been watered regularly.

Fortunately, temperatures have not been above normal, or the damage could have been worse. Established trees withstand drought better than those that have been planted in recent years. The rain this week should be a big help for the landscape plants that have needed moisture. As summer temperatures begin to increase, homeowners and landscape managers will want to continue monitoring the water status of their landscape plants and take appropriate action to avoid drought damage.

U.S. Dept of Ag, Forest Service, Southeastern Region

Bud blast and twig blight, caused by the fungus Briosia azaleae, is widespread throughout the natural range of rhododendron.

The terminal flower and leaf buds have brown to silver gray patches in the spring. The buds later develop small, black, hair-like projections on the surface and are prevented from developing fully. These inactive buds remain attached for 2-3 years. The rhododendron plant responds by sending out new shoots below the bud, giving a bunching appearance to the branch. In some cases branches may be killed when the affected bud occurs low on the branch.

This disease normally does not kill the rhododendron plant, but can reduce the number of flowers produced. The disease can be beneficial by forcing the plants to be more bushy and produce more flowers in a year when the current damage is low.

Although no practical control measures are available, the disease is not serious enough for alarm. Recognition of the symptoms described will help you distinguish bud blast and twig blight from more destructive disease and insect damage, and relieve concern over the possible loss of valuable plants.

June is the month that marks the placement of gypsy moth traps in Kentucky. This year, over 6,000 traps have been placed in the following counties: Bath, Bell, Boone, Boyd, Bracken, Breathitt, Bullitt, Calloway, Campbell, Carroll, Carter, Clay, Elliott, Fayette, Floyd, Gallatin, Grant, Greenup, Harlan, Harrison, Henry, Jackson, Jefferson, Jessamine, Kenton, Knott, Knox, Laurel, Lawrence, Lee, Leslie, Letcher, Lewis, Livingston, Lyon, Madison, Magoffin, Marshall, Mason, Menifee, Morgan, Oldham, Owen, Owsley, Perry, Pike, Pulaski, Robertson, Rockcastle, Rowan, Trigg, Trimble, Wayne, Wolfe.

The gypsy moth will usually fly around mid-July so it is important that these traps are up by the end of June. The trappers will check the traps once during the month of July to determine if there are any positive catches. Beginning the first of August, the trappers will begin removing the traps. Any area that caught a gypsy moth this year will be massed trapped next year in order to determine if the area has a population of moths or if it was an accidental introduction.

From US Geological Website: http://biology.usgs.gov/s+t/noframe/x193.htm

Purple loosestrife is not a problem (yet?) in Kentucky but we thought it would good for you to be have some information on this problem weed. It is a major problem in Indiana and Ohio and across the northern states where it has taken over wetland areas.

Purple loosestrife (Lythrum salicaria) is an exotic wetland perennial introduced to North America from Europe in the early 19th century. By the 1930's, the plant was well established along the New England seaboard. The construction of inland canals and waterways in the 1880's favored the expansion of purple loosestrife into interior New York and the St. Lawrence River Valley. The continued expansion of loosestrife has coincided with increased development and use of road systems, commercial distribution of the plant for horticultural purposes, and regional propagation of seed for bee forage. The plant now occurs in dense stands throughout the northeastern United States, southeastern Canada, the Midwest, and in scattered locations in the western United States and southwestern Canada. Newly created irrigation systems in many of the western states have supported its further spread.

Purple loosestrife is a classic example of an introduced species whose distribution and spread have been enhanced by the absence of natural enemies and the disturbance of natural systems, primarily by human activity. Although noted for the beauty of its late summer flowers, which also provide a nectar source for bees, loosestrife has few other redeeming qualities. Its invasion into a wetland system results in suppression of the native plant community and the eventual alteration of the wetland's structure and function. Large, monotypic stands not only jeopardize various threatened and endangered plants and wildlife, such as Long's bulrush in Massachusetts, small spikerush, Eleocharis parvula, in New York, and the bog turtle, Clemmys muhlenbergii, in the northeastern United States, but they also eliminate natural foods and cover essential to many wildlife, including waterfowl.

Purple loosestrife has many traits that enabled it to become a nuisance in North America. A single, mature plant can produce more than 2.5 million seeds annually; these seeds are long-lived and easily dispersed by water and in mud, adhering to aquatic wildlife, livestock, and people. Established plants are tall (about 2 m or 6.5 ft) with 30-50 stems forming wide-topped crowns that dominate the herbaceous canopy. A strong rootstock serves as a storage organ, providing resources for growth in spring and regrowth if the aboveground shoots are cut, burned, or killed by application of foliar herbicides. No native herbivores or pathogens in North America are known to suppress purple loosestrife.

No effective method is available to control loosestrife, except in small localized stands that can be intensively managed. In such isolated areas, the plant can be eliminated by uprooting by hand and ensuring that all vegetative parts are removed. Other control techniques include water-level manipulation, mowing or cutting, burning, and herbicide application.

Although these controls can eliminate small and young stands, they are costly, require continued long-term maintenance, and in the case of herbicides, are nonselective and environmentally degrading.

The most promising control measure for purple loosestrife is the application of classical biological weed-control procedures that use natural enemies like insects, mites, nematodes, and pathogens to reduce weed densities to tolerable levels. Results of insect surveys and screening tests conducted with the U.S. Department of Agriculture's Agriculture Research Service and the International Institute of Biological Control in Europe have identified five beetle species as potential control agents for purple loosestrife. Each species showed enough host specificity for purple loosestrife to be introduced with no ill effects to native North American plants.

Efforts are under way to rear large numbers of these insect species for further distribution and establishment in other states and provinces. A petition to introduce two of these beetles is under review by the USDA's Animal and Plant Health Inspection Service.

Initial collection of these insects in Europe for release into the United States is planned for 1994.

A cooperative state and federal program for the biological control of purple loosestrife focuses on an international environmental weed problem that cannot be controlled by conventional means. With support from federal and state agencies we have brought together an international scientific advisory staff to participate in and oversee the selection, screening, and introduction of an insect predator community that will provide a long-lasting biological control mechanism for loosestrife, and which will also develop a corresponding program of research and evaluation.

Purple loosestrife is now a naturalized weed that always will be a part of most North American wetlands. Researchers hope that introducing select insects will result in replacing monotypic stands of loosestrife by native vegetation and an overall decrease in the occurrence of the plant. We predict a reduction of purple loosestrife abundance over the next 15-20 years to about 10% of its current level over about 90% of its North American range.

By Paul Vincelli, Extension Plant Pathologist

For weeks now, patches or areas of many Kentucky bluegrass lawns have exhibited rust disease. Leaves of infect plants exhibit small (1/16 inch or less) pustules of orange-brown spore masses that erupt and break through the leaf surface. These pustules tend to be concentrated towards the top half of the leaf blade. Infected leaves initially are green but progress to yellow and tan.

The disease is most common is swards with a low level of nitrogen. Lawns with adequate nitrogen usually outgrow the disease. Remember that fall is the best time to apply most or all of the fertilizer, so don't try to correct the problem now with fertilizer. Applying fungicides now will do little to affect the health of the sward, since the disease has run its course for now. Watch these swards in the autumn, since the disease may pick up again then. Fertilizing after the heat of the summer is the best option for dealing with this disease. Preventive use of products containing propiconazole or triadimefon would be the best choice among fungicides, if that option appears desirable.

By Paul Vincelli, Extension Plant Pathologist

Brown patch was active on a number of cool-season grasses last week. This disease is one of the principal limitations to maintaining high-quality tall fescue lawns. Brown patch causes leaf spotting, leaf blighting, and even death of tall fescue tillers.

The leaf spots of brown patch in tall fescue are very characteristic: irregular spots that are olive-green when fresh or tan when dried, and which are surrounded by a thin brown border. These lesions can be readily distinguished from stresses due to other causes, which often cause a yellowing and die back beginning at leaf tip. When making a field diagnosis, be sure to check dead leaves for evidence of old brown patch lesions which may have led to the death of the leaves. The thin brown border will still show the outline on an old lesion even though the entire leaf may have been killed.

High nitrogen fertility in spring and summer can enhance disease activity, as can irrigating in the evening instead of the morning hours. Mowing height can also influence brown patch. At high mowing heights (three inches), expect more leaf blighting. At very low mowing heights (3/4 to one inch), expect more tiller death from root and crown infections by the brown patch fungus. Thus, a mowing height of 2 ½ inches represents a good balance for most situations.

For most lawns, I do not recommend fungicides for brown patch control. An exception sometimes exists in lawns which were newly seeded this spring, or even last fall. Such lawns sometimes suffer serious turf loss if high disease pressure develops. This is especially true if the lawn was seeded with too much seed, resulting in a very high tiller density. One of the most effective products for brown patch control is chlorothalonil, the active ingredient in Daconil and several other products. Unfortunately, since this is a contact fungicide, it must be sprayed at 10-14 day intervals in order to be effective under high disease pressure, which is more frequent than many turf managers and homeowners would like. A number of other fungicide choices are labeled for the home lawn, but many of these are not as effective.

More information on brown patch control is available in the UK Extension publication Brown Patch in Kentucky Lawns, ID-112, available from county Extension offices.

By David J. Shetlar, Ohio State Univ. http://www.ag.ohio-state.edu/~ohioline/hyg-fact/2000/2554.html

There are several species of sawflies that attack pines in Ohio, but the redheaded pine sawfly, Neodiprion lecontei (Fitch), can be especially troublesome. Because it has two generations per year, all the needles on a pine can be eaten in a single season. The spring generation can strip trees of their older needles and the summer generation can strip off the current year's needles. This total defoliation can result in death of the pine. This sawfly is found from Southeastern Canada through the eastern United States.

Redheaded pine sawflies prefer two and three needled pines including: Scotch, jack, shortleaf, loblolly, slash, red, mugho. It has also been rarely found feeding on white pine, Norway spruce, Deodar cedar and larch, especially if near its preferred pine hosts.

The first instar (newly hatched) larvae strip the needle surface leaving straw-like remains. Larger larvae eat the entire needle down to the sheath. The larvae are strongly gregarious, feeding in groups of 100 or more. Usually one year old foliage is eaten but all foliage may be eaten on heavily infested plants. If a tree is entirely defoliated before the larvae are mature, they will migrate to the nearest conifer. This is when they may attack non-preferred hosts.

Severe defoliation may kill plants while light defoliation will result in unsightly trees.

This pest overwinters as a prepupa (fully mature larva) in a cocoon in the duff under host trees. When spring arrives, the pupa is formed and the wasp-like adults emerge in a few weeks. Some prepupae have been known to remain dormant for two to three seasons before pupating. Females find preferred pines and deposit over 100 eggs in rows of slits along the edges of needles. Unmated females can still lay eggs but the offspring will all be males. Only fertilized females can produce more females.

The eggs hatch in about a month into caterpillar-like larvae. The young larvae only eat the surface of needles resulting in thin straw- like brown remains. Older larvae strip all the foliage down to the branch and can even gnaw on the branches if nothing else is available. The larvae take about one month to mature into one inch long, yellow bodied insects with black spots and orange-red heads. Mature larvae drop to the duff and pupate. From New York north, this insect has only one generation. South of this line, there are usually two generations and south of South Carolina, three generations are found.

In Pennsylvania, Ohio and Indiana, the first generation of larvae are found in May through early-June and the second generation is found in July, August and September.

Best control is obtained when the larvae are still small, so look for the needles with rows of spots which indicate egg laying, or look for the straw-like needles left by the young larvae feeding. Remember that some prepupae remain dormant for two seasons so elimination of active larvae in one season does not guarantee that the larvae will not be back for a second generation or the next year.

Strategy 1: Natural Controls - Several parasites, birds and viral diseases kill the larvae. Rodents often feed on the prepupae and pupae in the duff. These agents are sufficient in natural stands of pines but are not adequate in most urban areas, Christmas tree plantations or ornamental nurseries.

Strategy 2: Mechanical Control - Colonies of larvae can be easily removed by clipping off the infested branch. Place these branches in a plastic bag and destroy.

Colonies can also be knocked off by sharply striking the infested branch. Crush the larvae or knock into a pail of soapy water. If few colonies are present, they can be controlled using these methods but large infestations are better controlled by general spraying.

Strategy 3: Biorational Insecticide Sprays - Several horticultural oils (often called summer or verdant oils) and insecticidal soaps are labeled for control of sawflies on ornamentals. These usually work well when the sawfly larvae are small and thorough coverage of the colony can be achieved.

Strategy 4: Spot Sprays of Insecticides - Many aerosol or hose end sprayable insecticides are available for spraying of colonies. This is usually adequate for most home landscapes. Nurserymen and Christmas tree growers often carry a small hand pump sprayer with an insecticide mixed for spot treating colonies.

Strategy 5: General Insecticide Spraying - This sawfly rarely infests large acreages unless controls have not been used for several seasons. General sprays may be warranted if more than 25% of the trees are infested.