Inspector Findings in Kentucky

Transcription

1 Inspector Findings in Kentucky Volume XVII, Issue II Office of the State Entomologist June Inside this issue: Anthracnose on Shade Trees 2 Slug Sawflies on Roses 4 Maple Petiole Borer 4 Boxwood Leafminer 6 Office Update 7 What to look for 7 Cover photos Boxwood leaf miner damage and close up of leafminer Via Penn State University Cooperative Extension

2 Page 2 Anthracnose Diseases on Shade Trees By Nicole Ward Gauthier, Extension Plant Pathologist This spring has been cool and wet, leading to slow emergence of leaves on many shade trees. This combination of favorable weather conditions and slow leaf maturity created ideal conditions for development of anthracnose disease on several common shade trees. In short, the term anthracnose refers to a symptom that causes dark blotching and often leaf distortion. Defoliation (leaf drop) often occurs during severe infections. The disease often is not fatal, and a new flush of foliar growth immediately follows. Causal fungi may also infect twigs and branches, which develop into cankers and girdle stems. Anthracnose diseases are not caused by the same fungi. In fact, causal pathogens are quite host specific, meaning that the anthracnose pathogen on dogwood will not infect ash, etc. Symptom appearance and severity differ with each host and with climatic conditions. The fungal pathogens that cause anthracnose diseases have similar life cycles. Spore production occurs in spring during periods of rain; without rain, sporulation (spore production) is reduced and spore dissemination (spread) is not possible. Anthracnose fungi sporulate in spring as deciduous tree leaves emerge. Mature leaves are resistant to infection, but slow emergence in spring exposes tender leaves to fungal spores for an extended period of time. Ash anthracnose. Common symptoms include brown blotches (Fig1) along leaf edges. Leaf drop often results, and then new leaves soon emerge. Causal fungus: Discula umbrinella. Dogwood anthracnose. Leaf spots, leaf blight, and lower branch dieback may occur. The disease is most commonly observed on trees growing in shaded locations. This disease can lead to severe cankering, tree decline, and ultimately tree death. Causal fungus: Discula destructiva. Maple anthracnose. Symptoms begin as leaf spots (Fig 2) and may progress into shoot blight and shoot cankers. Leaf spots with brown, somewhat angular symptoms may be confused with tar spot (spots are round and black). Symptom development and susceptibility vary with tree species, but lesions often follow veins. Causal fungi: Discula sp. and Kabatiella apocrypta Oak anthracnose. Not commonly observed in Kentucky. Irregular brown spots develop on leaf tips and along veins. Causal fungus: Apiognomonia quercina. Sycamore anthracnose. Young, expanding leaves develop irregular dark, necrotic blotching centered along leaf veins or edges. These dark blotches may turn tan-colored as the diseased areas of the leaves dry out. Blighting of twigs or shoots may follow.

3 Page 3 Anthracnose Diseases on Shade Trees continued Trees produce new foliage rather quickly, but affected branches may remain crooked (lateral shoots became dominant when terminals were killed). Also affects London plane tree. Causal fungus: Apiognomonia veneta. For most trees, with the exception of dogwood, anthracnose disease is not lethal. However, repeated defoliation can be stressful to trees. Additionally, persistent rains and disease spread can lead to infection of twigs and branches. Good cultural practices are important to reduce disease: Anthracnose is favored by a moist environment. Select a planting site with a sunny eastern exposure to promote rapid foliage drying early in the day. Rake and destroy fallen leaves, as they can be a source of inoculum (fungal spores). Do not compost. Remove dead twigs and branches, as fungi can overwinter in dead wood. Reduce plant stress when possible. Avoid wounding, such as bumping with mowing equipment and making jagged pruning cuts. The dogwood anthracnose pathogen can enter trees through wounds to branches or trunks. Maintain mulch 2-3 inches thick over the root zone and beyond the drip line (not against the trunk) to help maintain soil moisture and to protect trees from lawnmower injury. Protect trees from drought. Water at least once a week during hot dry months using soakers or drip irrigation. Avoid overhead sprinklers; wet foliage favors sporulation and infection. Do not transplant dogwood trees from the wild, as they may be infected with anthracnose fungi. Purchase healthy trees from a reputable nursery. Diagnose and treat insect and disease problems as soon as possible. Plant disease resistant dogwoods such as C. florida 'Appalachian Spring' or oriental dogwoods (Cornus kousa) for high risk sites, such as those with heavy shade and nearby diseased trees. Fungicides are often not recommended. They can be costly and it is difficult to effectively cover large trees. Commercial nurseries, on the other hand, should protect trees with fungicides. Dogwoods that are threatened by anthracnose may benefit from early spring fungicide applications.

4 Page 4 Anthracnose Diseases on Shade Trees continued Figure 1 Figure 2 Slug Sawflies on Roses By Lee Townsend, Entomologist Slug sawflies are the caterpillar-like larvae of some wasps. Roseslug and bristly roseslug caterpillars cause distinctive feeding damage to leaves of wild and cultivated roses. Windowpane-like feeding scars caused by the early stages of the bristly roseslug were found on rose bushes this week in Russell County, signaling that these insects are active. The bristly roseslug is pale green and covered with many hair-like bristles. There are several generations each year so this insect can be a chronic problem during the summer. The roseslug is yellow-green and has only one generation a year. If practical, pick off and destroy infested leaves or wash the worms off with a strong water spray. Allowing small numbers of sawflies to feed gives predators a chance to take their toll. Contact products, like insecticidal soap, can provide good control but though spray coverage to the lower leaf surfaces is essential. Dusts can be effective but it is hard to get good overage when applying them. Roseslug sawflies are not true caterpillars so Bacillus thuringiensis insecticides (Bt) will not control them. Maple Petiole Borer Active By Lee Townsend, Entomologist Sudden leaf drop of sugar maples has been apparent in Marshall, McLean, Simpson, and Warren counties during the last week. While there are several potential causes, this has been the handiwork of the maple petiole borer, a small wasp. The result is leaf litter like that seen in this Figure 3. Sugar maple leaf drop. (Photos: G. Henson) picture.

5 Page 5 The larval stage of the wasp larva that burrows in leaf petioles, infested stem after leaf blade has fallen. 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 in an outbreak. While spectacular, the leaf drop has little effect on healthy trees. 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 harm 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. Figure 5. Blackened petiole due to maple petiole borer. (Photos: G. Henson) Figure 6. Blackened petiole due to maple petiole borer. (Photos: G. Henson)

6 Page 6 Boxwood Leafminer Penn State University Cooperative Extension College of Agricultural Sciences Boxwood leafminer, Monarthropalpusi flavus (Schank) is native to Europe and widely distributed throughout the United States. Its introduction dates back to the same time period the common boxwood was introduced into this country. The leafminer causes serious damage to boxwoods with heavily damaged plants become un-thrifty in appearance. Plants Attacked Both littleleaf boxwood, Buxus microphylla and Common Boxwood, Buxus sempervivens are commonly attacked, but there is resistance found in individual varieties of both species. Common boxwood cultivars with reported resistance are Handworthiensis, Pyramidalis, Suffruticosa and Varder Valley. Buxus microphylla var. japonica has also exhibited resistance to the boxwood leafminer. Life History Over-winter -The partly grown larvae of the boxwood leafminer over-winter within their mines in the leaves of the host plant. Spring - The larvae grow rapidly as the weather begins to warm. In late April, when weigela blooms, they turn into orange-colored pupae and emerge as a fly. After mating, the female inserts her eggs deep into the leaf tissue. She dies soon after and the eggs hatch approximately 3 weeks later, and the larvae commence feeding. Summer -The larvae continue to feed and grow slowly.. Damage Symptoms The larval feeding between the upper and lower leavescauses blistering and often discoloration. Lower leaf surface removed to expose young larvae of boxwood leafminer Insect Identification The eggs of the boxwood leafminer are white to transparent and can be seen by holding the leaf up to the light. The larvae are yellowish-white and approximately 1/8 inch long. The adult boxwood leafminer is an approximately 1/10 inch long, delicate, orangeyellow to red, gnatlike fly. Management Options Cultural -Selection of the more resistant varieties. Biological -Unfortunately there are few known natural enemies of the boxwood leafminer. Mechanical- Pruning the foliage before adult emergence or after egg laying ends will reduce the overall population. Chemical - Application of insecticide when the weigela is in bloom will reduce populations. Authored by: Katherine Mazzey, Penn State Extension Program Assistant, Michael Masiuk, Extension Agent, Penn State University Allegheny County

7 Page 7 Office Update Katie Joya, Nursery Inspector We ve begun all of our surveys for this year so you may be seeing Emerald Ash Borer traps or Gypsy Moth traps around the state. Two new counties are positive for EAB already this year Whitley and Carroll. Whitley is in the process of being added to the state quarantine. Carroll is already included in the quarantine. These finds were detected by examining ash trees in poor condition and finding EAB pupae and larvae., not by traps. We will take the traps down in September and screen them for any new finds. For more updates please visit our facebook page! What to look for in June... Birch leaf miner Birch foliage mid-june Dogwood sawfly Dogwood June through July Introduced pine sawfly White, red, Scotch, Austrian June and other pines Leafhoppers Foliage of many trees, especially June redbud Locust leaf miner Locust June Mimosa webworm Mimosa mid -June Nantucket pine tip moth Pine leaders early June Oak skeletonizer Oaks June Redheaded pine sawfly Pine needles mid-june through Sept, 2 to 3 generations/year Rose slugs Rose leaves mid-june Spruce needle miner Spruce June through hard frost John Obrycki, Ph.D: State Entomologist Joe Collins: Emerald Ash Borer Coordinator, pest surveys & nursery licenses joe.collins@uky.edu Carl Harper: Slow-the-Spread gypsy moth trapping coordinator, web design & phytosanitary certificates carl.harper@uky.edu JD Loan: survey supervisor, jdloan.1@juno.com Janet Lensing, PhD: State Survey Coordinator, pest surveys janet.lensing@uky.edu Jennie Condra: nursery inspections, pest surveys, outreach coordinator jennie.m.condra@gmail.com Katie Joya: pest surveys, nursery inspections, newsletter katie.kittrell@uky.edu Phone: (859) Fax: (859)