Inspector Findings in Kentucky

Nursery License Renewal

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

For those of you who live in the western part of the state, we will be at the Princeton Experiment Station field day on July 16 from 8 till 3. The experiment station is on KY 91S, 1.5 miles southeast of Princeton courthouse. Stop by and see us.

By John Hartman, Extension Plant Pathologist

Many Kentucky gardens feature iris plantings; these flowers are popular and well adapted. Frequent rains this spring have favored several diseases. Leaf spot has been appearing and corm rot has been devastating to individual plants in some iris beds this season.

Iris leaf spots. The fungus Didymellina macrospora causes the most prevalent leaf spot. On the leaves, oval brown spots with gray centers and water soaked margins can become so numerous that leaves become blighted and die. Iris in beds with this leaf spot disease have been observed to be almost completely killed by this fungus; the dead, tan and brown leaves remain upright making the disease a real eyesore in the garden. If the center of the gray spot is examined closely, dark fungal growth of Heterosporium iridis, the imperfect stage of the fungus, can be seen.

Bacterial leaf spot caused by Xanthomonas tardicrescens shows symptoms similar to those of the fungal leaf spot without the fungal growth. This disease occurs less frequently in Kentucky, but can also cause blighting.

Rust disease results in rusty-red pustules appearing on either side of affected leaves. The fungus, Puccinia iridis, can cause considerable damage to several iris varieties. Iris rust is relatively uncommon in Kentucky.

To control leaf spot diseases, remove blighted leaves during the season, and remove and destroy all foliage in the fall. Fungicides such as Daconil 2787, mancozeb, Cleary's 3336, and Chipco 26019 can be used to protect iris from Didymellina leaf spot. Fungicides will not control bacterial leaf spot.

Rhizome and bulb disorders. Bacterial soft rot is a serious disease of the rhizome that can appear in newly planted as well as mature iris plantings. The pathogen, Erwinia carotovora causes a foul-smelling soft decay of the rhizome. The bacterium gains entrance into the plant through wounds in young leaves made by young larvae of the iris borer. Soft rot is prevented by planting healthy rhizomes and preventing the iris borer damage.

Botrytis convoluta and Sclerotium rolfsii are two fungi that can cause rhizome and crown rot diseases of iris. The former produces irregular black sclerotia in the decaying rhizome, while the latter produces small spherical sclerotia on the rotted leaf bases. Neither produces a foul-smelling decay. When affected rhizomes are found, they should be removed and destroyed.

Bulbous iris are subject to several bulb diseases and decays. Diseases such as black rot, ink spot, Fusarium basal rot, and blue mold cause decays of bulbous iris. Sort out and destroy diseased bulbs as they occur.

By Ric Bessin and Lee Townsend, Extension Entomologists

Although the report was from corn, the Japanese beetle isn't a very picky eater so it is just as appropriate to announce its activity in this newsletter. Also, this report came from Carlisle county, reminding us that this insect has made its way across the state. Surveys over the past few years have shown the spread of the Japanese beetle but populations have been relatively localized in many of the western counties now included in its range.

Plant Selection- The best way to avoid perennial battles with adult Japanese beetles is plant selection. Certain plant species (see ENT-5, Japanese Beetles In the Urban Landscape available at your county extension office) are much preferred by the beetles, and are poor choices for new plantings in beetle-prone areas. ENT-5 also lists species of trees and shrubs that are relatively unattractive to beetles. Other tactics must obviously be used for susceptible plants that are already established in the landscape.

Physical Removal and Exclusion- Removing beetles by hand may suffice for small plantings when beetle numbers are relatively low. By not allowing Japanese beetles to accumulate, plants will be less attractive to other beetles. One of the easiest ways to remove beetles from small plants is to shake them off early in the morning when the insects are sluggish. The beetles can be killed by shaking them into a bucket of soapy water. Small plants such as roses can be protected by covering them with cheesecloth or other fine (< 1/4") netting during peak beetle activity.

Insecticides- Various insecticides, including Sevin (carbaryl), Scimitar, Tempo, Talstar, Turcam, Dursban, malathion, and Orthene are labeled for control of adult Japanese beetles. Sevin is very effective and is the product of choice for most homeowners. Foliage and flowers should be thoroughly treated. The application may need to be repeated at 7-10 day intervals to prevent reinfestation during the adult flight period, or after heavy rains. Follow label directions, and avoid spraying under windy conditions. Insecticidal soaps will control beetles that are hit by the spray, but they provide no residual protection. Botanical insecticides such as neem or pyrethrum are generally ineffective.

Japanese beetle traps continue to be sold in many garden centers. These traps catch large numbers of beetles, but do not reduce damage to plantings. Research conducted by UK's Horticultural Entomology Lab showed that traps attract many more beetles than are actually caught. Consequently, susceptible plants along the flight path of the beetles and in the vicinity of traps are likely to suffer more severe damage than if no traps were used at all. If clients wish to experiment with traps, they should be placed far away from gardens and landscape plants.

By John Hartman, Extension Plant Pathologist

There have been recent observations of decline and death of white pines in landscapes in several central Kentucky locations. In most cases the pines were 15-20 years old, established in the landscape for at least 10 years and showed no apparent problems until recent years.

Symptoms observed now. In at least one case involving a group of over 50 pines, several almost a foot in diameter had been cut down; other pines nearby showed poor shoot elongation, needle browning, and lower branch death; and pines still farther away were healthy. Some declining pines showed patches of resin at the base, and when the bark was removed from the trunk and adjoining buttress roots, a resin-soaked dark brown staining or streaking was evident in the cambium and wood. Others with foliar symptoms had no basal resin patches, but when buttress roots and lower trunk were examined, the resin-soaked brown streaking under the bark was again present. In addition, many diseased trees showed excess resin flow from parts of the trunk where diseased branches had previously been removed. The indications were of a progressive soilborne disease affecting the pines - white pine root decline caused by the fungus Verticicladiella procera, also called Leptographium procerum.

White pine root decline vs. white pine decline. White pine decline is a common problem in many parts of Kentucky, but could be confused with white pine root decline. White pine decline is not infectious - it is associated with compacted soils and those that have a high pH or high clay content.

However, like white pine root decline, it often only begins to appear in previously healthy plantings after the trees become 15-20 years old. One would not expect white pine decline to begin in one part of the planting and gradually spread from there. In one case where white pine root decline was active, the well-drained silt loam soil with little clay had been treated with sulfur over the years and the pH was in the range of 5.5-6.5, which should have been a favorable growing site for white pine. In addition to site differences, white pine root decline symptoms - the resin-soaked dark brown stained buttress root and trunk base - can help one to differentiate one disease from the other in the field.

Disease management. White pine root decline is not curable and may be difficult to prevent in some sites. We have observed it on well drained as well as on wet sites. White pine root decline is known to be more of a problem for pines that are growing in stressful circumstances such as root and trunk wounding, air pollution exposure, and infection by other root decay fungi. In addition, the fungus can be vectored by trunk boring insects, but their exact role here is not well defined. White pines are native to some parts of eastern Kentucky where it grows in moist sites with acid, sandy, soils. In other parts of Kentucky, there are exceptional long-lived white pines growing out of their native sites. However, if white pines are being planted in landscapes to last a long time, premature decline and death is a risk that must be considered in most locations. The best advice is to provide white pines with good growing conditions.

by Lee Townsend and Joe Collins

Sawflies are members of the same insect order (Hymenoptera) that includes ants, bees, and wasps. The females of this group of non-stinging wasps have a saw-like blade at the tip of the abdomen that is used to cut slits into plant tissue into which they will deposit eggs. Many sawflies feed on conifers.

Some species feed only upon old needles; others feed only on new growth. They generally occur in groups and can cause serious defoliation. Different species are active at different times of the year.

Sawfly larvae resemble the caterpillars of moths and butterflies in body form but a closer look can easily determine the difference. Butterfly and moth caterpillars have 2 to 5 pairs of fleshy prolegs on the abdomen; sawflies have more than 5 pairs. Differentiating sawflies from other caterpillars is important in that a biological insecticide that works well against butterfly and moth larvae is not effective against sawflies.

The introduced pine sawfly was first detected in the Commonwealth in 1992. It prefers eastern white pine but will also feed upon Scotch, red, Austrian, jack, and Swiss mountain pine. Short leaf and Virginia pines have been attacked but usually not heavily damaged. The larvae feed upon the needles. Defoliation is most severe in the upper half of tree crowns, but heavily infested trees can be completely defoliated in a single season. When this happens late in the season, after the winter buds have been formed, many branches and occasionally trees may be killed.

There are two generations each year. The second overwinters in 1/4" long, bullet-shaped brown cocoons that can be found attached at the base of small branches, in bark crevices, or on the ground. The adults will generally emerge during May and early June. Females lay about 10 eggs in slits cut in the older needles. Young larvae will feed in groups and as they get older will begin to feed singly. They are about 1" long when mature. The larvae have a black head and black body covered with yellow and white spots.

The first generation larvae prefer to feed on the previous year's needles and will finish development in July. The second generation feeds on both old and new needles and is full grown in late September.

Young larvae will feed on the more tender outerparts of the needles while the older larvae feed on the entire needle. Natural control in the form of very low or fluctuating temperatures, heavy rainfall during the egg and early larval stages, and bird predation may serve to keep the population at a minimum.

The redheaded pine sawfly is one of the most destructive of the group. It tends to attack trees in the 1' to 12' range, especially those already under stress due to poor site or severe competition from other trees. This species attacks jack, mugho, short leaf loblolly, slash, red, Scots, and other 2- and 3-needled pines. These distinctive larvae have red heads with 2 black eye spots and a yellow-white body with six rows of black spots. When full grown, the caterpillars are 1" to 1-1/4" long.

There can be two or three generations each year, with the first appearing in the spring. The larvae feed gregariously on new and old needles as well as the tender bark of young twigs. They generally feed downward from the top of the tree. After complete defoliation, they may crawl over ground for several yards to find new foliage.

The Virginia pine sawfly primarily attacks Virginia pine but will feed upon short leaf pine and loblolly.

Attack by this insect produces the most damage when they produce severe defoliation over several years or under drought conditions. Young larvae are light green with a black head. When full grown (about 3/4" to 1" long), the light green body is spotted or has longitudinal black stripes.

This sawfly spends the winter in the egg stage. The newly hatched larvae feed in groups on the previous year's growth, just below the tip. They ultimately eat all of the needle except the basal portion within the sheath. There is one generation each year with the larvae completing development in mid-May.

The loblolly pine sawfly, a long time pest in Arkansas, has attacked loblolly pines in western Kentucky during some years. The larvae, about 1-1/4" long when full grown, have a chocolate brown head and dull green body. There are heavy black stripes along each side with two lighter stripes below them. Like the Virginia pine sawfly, this insect is a spring and summer feeder. It is found most often on medium to large trees in forest stands. A virus disease and cold, rainy spring weather often provides adequate natural control.

Sawfly populations are usually controlled by combinations of natural enemies, predators, starvation, disease, or unfavorable weather. Outbreaks can occur when natural control does not produce high mortality. Regular inspection of pines will help to detect sawfly infestations before the larvae reach a size that can cause significant defoliation. Since eggs are laid in clusters, feeding by groups of larvae can cause unsightly damage to ornamental or landscape plantings as well as tree nurseries.

If only a small number of colonies are present and accessible, they can be handpicked, shaken off, or pruned from the tree and destroyed. Acephate (Orthene), carbaryl (Sevin), or chlorpyrifos (Dursban) are among the insecticides that may be used for sawfly control. Insecticidal soaps may be effective if the insects are contacted directly by the spray. Frequent inspection of trees will allow early detection of damaging infestations.

from North Carolina Extension Service website

Sooty molds are microscopic threads that become abundant enough to form easily visible spots. When very abundant, sooty molds cause plants to appear dark and sooty or almost uniformly charcoal gray. Occasionally, sooty molds form a continuous thin sheet that eventually peels away from the plant surface like delicate black tissue paper. Microscopic examination reveals the sooty mold threads may be matted down or more or less cemented together. Capnodium sooty molds have various kinds of spore forming structures.

Sooty molds occur in all parts of North America. Capnodium citri is associated with whiteflies and scale pests on citrus. Capnodium elongatum is associated with scale pests of tuliptree, oleander, osmanthus and other ornamental plants. Other species of Capnodium are associated with insect pests of fig, crape myrtle, azaleas and many other plants. Scorias spongiosa is associated with aphid and scale pests of alder, pine, beech and other trees. Fumago vagans is associated with sucking pests of linden and other trees, shrubs and even house plants. Sooty molds are not plant parasites; they develop in honeydew, a sweet, sticky liquid excreted by aphids, scales and other sucking insect pests that feed from the phloem tissue. However, sooty molds lessen the aesthetic value of ornamental plants, and lower the vigor of plants by blocking sunlight essential for photosynthesis. The combination of feeding by a large number of aphids or scales and the heavy coating of sooty molds may drastically reduce the vigor and beauty of ornamental plants.

Sooty molds are associated with sucking insect pests (aphids, scales, mealybugs, psyllids) that extract sap from the phloem tissue. Soon after a plant is heavily infested with such a pest, it is usually covered with honeydew. Sucking pests ingest copious amounts of sap to extract nutrients. Much of the water and sugars in the sap pass though the insect are excreted. Unless washed off by rain, the honeydew clings to the plant (and objects below). Spores or fragments of sooty molds are blown are carried to the honeydew and new colonies of sooty mold develop. Although the fungal threads may adhere tightly to the plant surface, sooty molds do not parasitize plant tissue; they develop exclusively on honeydew. However, even after the source of honeydew is eliminated, sooty molds may adhere to plants and other objects for months afterward.

The first step in control of sooty molds is to suppress the aphids, scales or other pests that are excreting the honeydew on which sooty molds subsist. If one of the horticultural oils is used for control, it also has the advantage of helping to loosen sooty molds form the plant surface. This hastens the weathering away of the sooty molds. Horticultural oils are formulated by many companies are available through garden centers, hardware stores, and like establishments. The rates of application vary with time of year. If horticultural oils are applied to tender, new growth, damage to the plant may occur.

by John Hartman, Extension Plant Pathologist

Powdery mildew disease is beginning to appear in several woody plants in the landscape. It is highly visible, as usual, on lilacs, susceptible crab-apples, and on vigorous shaded sprouts of oaks, as well as on flowering dogwoods. Based on how this disease has developed in recent years, the most serious problem now appears to be dogwood powdery mildew. Small patches of white mildew growth are now highly visible and infected leaves are beginning to fade.

Symptoms. The mildew is made up of delicate, cobweb-like strands of fungus tissue covered with microscopic colorless asexual spores. Although mildew fungi grow mainly over the surface, they also penetrate the leaf surface with numerous fine filaments, which extract nutrients from the host plant. Heavily mildewed leaves may be distorted, turn yellow, dry up, and fall prematurely. Reduced flower quantity and quality the next season are also involved. Mildews appear most commonly toward the end of summer and in late fall and are most prevalent on succulent growth in shaded and damp locations. In the fall, minute, spherical, black bodies called cleistothecia - fruiting structures of the sexual stage of the fungus - may be visible to the unaided eye in the grayish white areas. The spores of the fungus may overwinter in these bodies. Some powdery mildews overwinter vegetatively in dormant buds of the infected tree.

Cause. There are a number of distinct species of powdery mildew fungi, which can be distinguished only by microscopic examination. Two species, Microsphaera pulchra and Phyllactinia guttata have been reported on dogwood. In Kentucky, we see both types with cleistothecia firmly embedded in the fungal mat on leaf surfaces; on leaves harvested without fruiting bodies, the cleistothecia develop in the laboratory.

Control. Resistant cultivars of flowering crabapples are available and offer an excellent means of control. Cornelian cherry and Kousa dogwoods are resistant, hybrids of Kousa and flowering dogwood and the flowering dogwood cultivar 'Cherokee Brave' are partially resistant, and all other flowering dogwoods are highly susceptible. Beneficial management practices such as pruning out infected twigs, raking up infected leaves, improving air movement around the trees, and increasing the amount of sunlight reaching them can often reduce severity of the disease. Dusting or wettable sulfur fungicides control powdery mildew. Other fungicides such as Banner Maxx, Bayleton, Benomyl, Cleary's 3336, Eagle, Immunox, Rubigan, and Strike are also effective for dogwood powdery mildew.

by Lee Townsend, Extension Entomologist

A sudden drop of many sugar maple leaves in June may be due to injury by a small wasp larva that burrows in leaf petioles (stems). The stems usually break at a darkened area near the leaf blade.

Usually infestations are limited to sugar maples and only about 25% to 30% of the leaves fall to the ground. While spectacular, the leaf drop has little effect on tree health. Buildups of scales or aphids, or drought stress can cause leaf loss but these typically occur later in the year. Leaf drop due to borers is seen earlier in the season and the leaf blades may still be green. Leaves from trees stressed by sucking insects or drought usually have turned yellow before they drop. Splitting the petiole carefully near the leaf blade should reveal the larva or the tunnel.

There is one generation each year. Infestations begin as the adults, small wasps about 1/6" long, appear in May and lay their eggs in petioles near the leaf blades. Legless, white grubs with distinct light brown heads hatch from the eggs and tunnel inside the leaf stem for 20 to 30 days. The weakened stem breaks and the leaf floats to the ground.

The borer larvae generally remain in the portion of the stem left on the tree. About 10 days after leaf drop, the rest of the stem falls to the ground. The mature larva, about 1/3" long, leaves the stem through a hole in the side and burrows into the soil. It will change to the pupal stage and remain in the soil until the following spring.

Maple petiole borer infestations are infrequent and unpredictable. Also they do not appear to arm tree health so insecticidal control is not recommended. In addition, probably preventive treatments, applied well before leaf drop, would be necessary. It may be possible to reduce future infestations by picking up and destroying infested stems, the short sections without leaves, about 7 to 10 days after the first leaves fall. This sanitation program needs to be continued throughout the leaf drop period and must include all infested trees in the vicinity to be most successful. Raking and disposing of the leaves will not reduce the population because the insects are not in that portion.

By John Hartman, Extension Plant Pathologist

The leaves of oaks, azaleas, blueberries and other woody plants are appearing very yellow in some landscapes. This condition, called chlorosis, occurs when there is a reduction in the normal amount of chlorophyll in the leaves. This loss of chlorophyll reduces the efficiency of the leaf in manufacturing food. Chlorotic leaves may result from fungus, virus, or insect attack; low temperatures; toxic materials in the air or soil; excess soil moisture; and too much or not enough of soil minerals such as iron. Chlorosis of azaleas and pin oaks, for example, associated with iron deficiency is really due to non-availability of iron rather than with the lack of iron in the soil. This is especially true in soils containing limestone, ashes, or other alkaline materials, where the pH of the soil ranges from 6.7 to 8.5. Iron may be present in such soils, but in a form that cannot be absorbed by the plant.

Symptoms. The leaves of affected trees first turn uniformly yellowish green, or they may remain green along the veins but turn yellow between the veins. The terminal growth of twigs is reduced, and the tree or shrub is generally stunted. The tissue between the leaf veins or along the leaf edge may die on trees affected for several years with chlorosis. Eventually whole branches or the entire tree or shrub may die prematurely unless the condition responsible is corrected. New growth is usually more severely affected than growth produced earlier in the season.

Iron chlorosis imposes a stress on trees and shrubs with the problem. Oaks growing under stress are often attacked by leaf-spotting fungi such as Tubakia dryina, cause of Actinopelte leaf spot, a disease that often results in premature defoliation. Azaleas and blueberries are subject to canker diseases such as Botryosphaeria canker which might not otherwise attack plants growing well.

Control. Chlorosis caused by deficiency or non-availability of iron can often be corrected by special treatments. Lowering the soil pH from the alkaline to the acid range makes iron and other minerals in the soil more available to plants needing these elements. Soils can be acidified using granular or powdered sulfur. Soluble iron can also be applied to the foliage. Iron solutions may also be applied by injection or implantation of iron into the trunks of trees, but this creates wounds. Methods for correcting iron deficiency chlorosis are discussed in U.K. Cooperative Extension publication ID-84 available at your county extension office.