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Wooly Aphids Attack Hackberry Trees09-12-06 | News

Wooly Aphids Attack Hackberry Trees

Study results indicate that soil injections of imidacloprid (Merit 2F, Bayer Environmental Sciences) applied three weeks after trees leaf out, when aphid infestations can be confirmed, are as effective as applications made before bud break when treatments may be applied unnecessarily to un-infested trees.

Researchers have found a way for growers and homeowners to save money and time by knowing when and how much insecticide to apply to control the Asian hackberry woolly aphid. The aphid showed up on Chinese hackberry trees in Davis and other Sacramento Valley cities in 2002. First found in Florida and Georgia in the late 1990’s, it spread rapidly across the south and into California. The fuzzy white insects found on the tops and bottoms of leaves cause the leaves to drip sticky liquid all over everything beneath them. This sugar excretion draws ants, and a black mold may grow on surfaces covered with it. Even large populations of aphids do not kill the trees, but the amount of sticky goop is a major nuisance in many urban settings.

Hackberry woolly aphids secrete pale bluish or white wax over their bodies. These fuzzy masses are each about 1/10 inch or less in diameter. This waxy covering usually obscures the insect’s gray, green, or yellow body. Treatments can be applied after populations have been confirmed through monitoring, checking leaf samples and using water sensitive cards to measure honeydew are reliable monitoring methods to determine the number of aphids present.

Users can then see if the aphid population is high enough to require insecticide treatment. Researchers monitored aphid and predator populations for three seasons. Aphid densities were found to be highest in the spring and fall, with lower densities during the mid-summer months. No treatments should be conducted during fall, because hackberry leaves.

For information about aphid management, visit www.ipm.ucdavis.edu.