JULY 2016 OFFICE OF THE STATE ENTOMOLOGIST VOLUTELLA BLIGHT PAGE 2 FOURLINED PLANT BUG PAGE 5 VOLUME XVIIII, ISSUE III ANTRHACNOSE ON SHADE TREES PAGE 8 INSPECTOR FINDINGS Plant Bug illustrations from Encyclopædia Britannica, www.britannica.com University of Kentucky Department of Entomology Office of the State Entomologist S-225 Ag Science Ctr N Lexington, KY 40546-0091 Phone: (859) 257-5838 Fax: (859) 257-3807 1
Volutella Blight of Boxwood BY KIM LEONBERGER, EXTENSION ASSOCIATE AND NICOLE WARD GAUTHIER, EXTENSION SPECIALIST Volutella blight is the most common disease of boxwood in the landscape. Volutella blight is caused by an opportunistic fungal pathogen that attacks leaves and stems of damaged or stressed plants. Winter injury, poor vigor, and wounds increase risk for Volutella blight. Volutella Blight Facts Leaves begin to turn red or bronze, eventually becoming straw-yellow (Figure 1). Branches die back from tips and girdling may occur lower on stems (Figure 2). Bark may also be loose on infected branches. In moist, humid weather, salmon-to-pink fruiting structures may be visible (Figure 3). American and English boxwood are susceptible. Disease development is favored by high humidity and temperatures between 65 and 75 F. The pathogen survives winter on affected branches and leaves from the previous season. Caused by the fungus Pseudonectric buxi (asexual stage Volutella buxi). Management Options Maintaining a sanitation program and promoting plant vigor are critical for disease management. Prune diseased branches. Prevent wounding, including improper pruning cuts. Maintain plant health with proper nutrition and irrigation practices. Avoid excess water. Maintain good air circulation by sufficiently spacing plants or by pruning dense growth. Gather and destroy plant debris. If disease continues to be a problem after following other management practices, fungicides may be used preventatively beginning in spring. Homeowners may use fungicides that contain mancozeb or copper. Always follow label directions when utilizing fungicides 2
Figure 1: Infected leaves turn from red/bronze to a straw-yellow color. (Photo: Adam Leonberger, UK) 3
Figure 2: Girdling or loose back may be present on lower stems. (Photo: Adam Leonberger, UK) Figure 3: Salmon or pink fruiting structures may be visible in periods of moist, humid weather. (Photo: Paul Bachi, UK) 4
Additional Information on Volutella Blight Homeowner s Guide to Fungicides (PPFS-GEN-07) Landscape Sanitation (PPFS-GEN-04) Woody Plant Disease Management Guide for Nurseries and Landscapes (ID-88) Boxwood Diseases (Penn State Extension) Boxwood (Buxus)-Volutella Leaf and Stem Blight {Canker} (Pacific Northwest Plant Disease Management Handbook) Volutella Blight Boxwood (Home & Garden Information Center, University of Maryland Extension) Fourlined Plant Bug BY LEE TOWNSEND, EXTENSION ENTOMOLOGIST The fourlined plant bug, with a host range of over 250 species, is one of the most destructive sap-feeding insects. It injects a powerful digestive enzyme that destroys cells around feeding sites, producing almost instantaneous symptoms (Figure 4). Damaged areas shrink and collapse, producing necrotic areas (Figure 5) that may subsequently drop out, leaving small shot-holes. Feeding injury can cause distortion of expanding leaves. Figure 4. A small dark spot is usually visible in the center of the feeding lesion, which is usually more uniform than a bacterial leaf spot.(photo: Lee Townsend, UK) 5
Figure 5. New (light green) and older (dark) feeding spots caused by the fourlined plant bug (Photo: Lee Townsend, UK) Insect Development Fourlined plant bugs pass winter as eggs in host plant tissue. Eggs hatch in early spring and the nymphs begin to feed. Damage is common on perennials (mint, composites, as well as shrubs, such as azalea, forsythia, viburnum, etc.) Feeding damage from their red and black nymphs (Figure 6) is intense during the 4-week developmental period because they do not travel far; their movement is limited to crawling on or between adjacent, touching plants. The adult fourlined plant bug, which appears in early June, has a yellow-green body with a yellow-orange head. They have four parallel black lines (Figure 7). Winged adults live for several weeks and because they can move easily, their feeding damage is usually spread over many landscape plants. There is one generation each year. 6
Figure 6. Fourlined plant bug nymph and feeding spots. (Photo: The Ohio State University Plant Bug Fact Sheet) Figure 7. Adult fourlined plant bug (Photo: Lee Townsend, UK) Management Insecticidal soap can provide acceptable control of immature stages but is less effective against the mobile adults because the insects must be hit with spray droplets to be killed. Physical protection of herbs and mint with a cheesecloth covering may be an acceptable alternative for small plantings. 7
Anthracnose Diseases on Shade Trees BY NICOLE WARD GAUTHIER, EXTENSION PLANT PATHOLOGIST AND KIM LEONBERGER, EXTENSION ASSOCIATE This spring has been cool and wet, leading to slow emergence of leaves on many shade trees. This combination of favorable weather and slow leaf maturity created ideal conditions for development of anthracnose disease on several common shade trees. The term anthracnose refers to the dark blotching (necrotic) symptom common to these diseases. When expanding leaves are affected, leaf distortion frequently results (Figure 8). Defoliation (leaf drop) often occurs during severe infections. The disease is generally not fatal, and a new flush of foliar growth soon follows defoliation on some tree species. Causal fungi may also infect twigs and branches resulting in cankers that girdle stems (Figure 9). Figure 8: Symptoms of anthracnose on shade trees include dark blotches and leaf distortion. (Photo: Nicole Ward Gauthier, UK) 8
Figure 9: The fungal pathogens that cause anthracnose may also infect twigs and branches. Resulting cankers girdle affected branches. (Photo: John Hartman, UK) Symptoms The fungal pathogens that cause anthracnose diseases are quite host-specific, meaning that the anthracnose pathogen on oak will not infect ash, etc. Symptom appearance and severity differ with each host and with climatic conditions. Ash anthracnose: Common symptoms include brown blotches along leaf edges. Leaf drop often results, and then new leaves soon emerge. Causal fungus: Discula umbrinella. Maple anthracnose: Symptoms begin as leaf spots 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 diseased areas of leaves dry out. Blighting of twigs or shoots may follow. Trees produce new foliage rather quickly, but affected branches may remain crooked (lateral shoots become dominant when terminals are killed). Also affects London plane tree. Causal fungus: Apiognomonia veneta. Managing Shade Tree Anthracnose 9
For most trees, 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: Select a planting site with a sunny eastern exposure to promote rapid drying of foliage 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 diseased wood. Reduce plant stress when possible. Avoid wounding, such as bumping with mowing equipment or making jagged pruning cuts. Maintain mulch 2 to 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. Diagnose and treat insect and disease problems as soon as possible. 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. Resources Considerations for Diagnosis of Ornamentals in the Landscape (PPFS- GEN-15) Landscape Sanitation (PPFS-GEN-04) Shade Tree Anthracnose (PPFS-OR-W-23) Woody Plant Disease Management Guide for Nurseries and Landscapes (ID-88) Dr. Reddy Palli, Ph.D: State Entomologist Joe Collins: joe.collins@uky.edu Pest surveys & nursery licenses Carl Harper: carl.harper@uky.edu Slow-the-Spread gypsy moth trapping coordinator, phytosanitary certificates Katie Joya: katie.joya@uky.edu Pest surveys, nursery inspections, newsletter editor Jennie Condra: jennie.condra@uky.edu Outreach coordinator, nursery inspections, pest surveys Janet Lensing, PhD: janet.lensing@uky.edu State Survey Coordinator JD Loan: jdloan.1@juno.com Survey supervisor 10