Loudoun County Master Gardeners

Loudoun County Master Gardeners

Emerald Ash Borer

The emerald ash borer has been discovered in Herndon and Springfield in July 2008.

Emerald ash borer (EAB), Agrilus planipennis Fairmaire, is an exotic beetle that was discovered in southeastern Michigan near Detroit in the summer of 2002. The adult beetles nibble on ash foliage but cause little damage. The larvae (the immature stage) feed on the inner bark of ash trees, disrupting the tree's ability to transport water and nutrients. Emerald ash borer probably arrived in the United States on solid wood packing material carried in cargo ships or airplanes originating in its native Asia.

It attacks only ash trees (Fraxinus spp.).
Adult Beetles are metallic green and about ½-inch long.
Adults leave a D-shaped exit hole in the bark when they emerge in spring.
Woodpeckers like EAB larvae; heavy woodpecker damage on ash trees may be a sign of infestation.

In 2003 Emerald Ash Borers were found in ash trees in Fairfax County. Those trees were destroyed. Now they have been found in Clinton Md. and officials worry they could spread to other areas. The state is in the process of marking trees to cut down. All ash trees within a mile and a half of the infested ones will have to be destroyed, and officials have issued a quarantine until they figure out how to get rid of the beetle.

For more on the Emerald ash borer see:

http://www.na.fs.fed.us/fhp/eab/

http://www.emeraldashborer.info/

http://www.aphis.usda.gov/plant_health/plant_pest_info/emerald_ash_b/index.shtml

Cedar apple rust

Infected apple and apple leaves (below)

Infected cedar (below)

During warm rainy days in late April and early May, cedar trees infected with the cedar-apple rust fungus will develop bright orange, gelatinous galls.

Cedar-apple rust is an interesting disease. It requires both an apple and cedar or juniper to complete its life cycle. On the cedar, the fungus produces reddish-brown galls that are up to golf-ball size on young twigs. During wet weather these galls swell and begin to push out bright orange gelatinous tubular structures. Wind carries fungal spores from these gelatinous structures to susceptible apple or crabapple cultivars.

For more information see:

http://www.caf.wvu.edu/kearneysville/disease_descriptions/omcar.html

http://plantclinic.cornell.edu/FactSheets/cedar-applerust/cedar-applerust.htm

Boxelder bugs

Boxelder bugs are about one half inch long. The brownish-black adults have very visible red markings on their backs. Boxelder nymphs look like the adults except they are smaller and a bright red. The bugs feed primarily on Boxelder trees, but will also feed on maple, ash, cherry, apple, grape, peach, and strawberries.

Boxelder bugs are harmless. If they invade your home, vacuum them up.

Dogwood Anthracnose

Two different kinds of anthracnose diseases may occur on dogwood.

Spot anthracnose. Symptoms of spot anthracnose include tiny leaf and bract spots, about the size of a pinhead, with whitish centers and purplish borders. this usually does not cause serious damage to the tree.

Dogwood anthracnose. Symptoms of Discula anthracnose (dogwood anthracnose) include irregular, small to large brown blotches with purplish borders on leaves and bracts, lower branch dieback, and trunk cankers that culminate in death of the tree.

Spray with a fungicide containing mancozeb (e.g. Manzate 200, Dithane M-45) at budswell and twice again during leaf expansion (in most years, this would be at 10-14 day intervals). Control of this anthracnose disease on dogwood is described in VCE Publication 450-611W, Foliar Diseases of Dogwood.

To help prevent dogwood anthracnose, plant your tree in a sunny spot with good air circulation.