Manage Effects of Moth Infestation
The Athens-Clarke County Unified Government’s Environmental Coordinator is urging citizens to look for signs of the black-dotted brown moth (Cissusa spadix). Athens has experienced significant infestations of this pest for the past four years. In recent years, the outbreak has expanded to include Athens-Clarke, Jackson, Madison, Oglethorpe, and Oconee County. The outbreak is expected to be more widespread this year, however, with less damage and defoliation to the individual trees. Learn how to manage effects of moth infestation.
The caterpillar tends to feed on tree species from the white oak group, with a special preference for post oaks (Quercus stellata). High densities of the caterpillar will completely defoliate these trees. Repeated defoliations can lead to crown dieback, tree decline, and risk for early death.
Typically, owners do not notice infestation until the tree experiences rapid and nearly complete defoliation. Other signs of an infestation include unusual loss of bark plates due to predators feeding on the inchworm-like caterpillars underneath that secrete a reddish brown liquid when disturbed and large amounts of frass (insect excrement) accumulated beneath the trees.
Dr. Kamal Gandhi, a forest entomologist at the University of Georgia, has already begun to see signs of emergence. Control methods should be taken immediately. If this is the first year property owners have noticed the insects, it is recommend that they either closely observe the infestation without taking preventative action, take low impact actions to increase natural predation of the caterpillars, or prevent them from climbing the tree.
John Ritzler of New Urban Forestry in Athens, GA, suggests encouraging habitat for natural predators that feed on the caterpillars such as birds and squirrels to reduce the number of insects; providing bird feeders near white oaks can increase the presence of these natural predators.
Other methods of low impact control include the use bug barriers to trap the caterpillars in the lower trunk so they are unable to feed on the leaves of the trees. While many barriers are commercially available, several local residents have established that a 4-6” wide band of vegetable shortening around the trunk provides an effective, low cost method of exclusion. More information on the management of this pest can be found at the Environmental Coordinator’s website at http://www.athensclarkecounty.com/green.
Smaller oaks that have experienced defoliation for a number of years can be treated with a bacterial insecticide called Bacillus thuringiensis (Bt). Specimen trees that have experienced three or more years of defoliation can be treated with the insecticide Imidacloprid (sold as Bayer Tree and Shrub Insect Control, Dominion, or Merit). Use this treatment with caution and only on specimen trees and trees at risk for death. Many insects, including natural predators, can be affected by this treatment.
Prevention and treatment is the key to reducing the impacts of the black-dotted brown moth. Simple, inexpensive measures can insure that these pests do not defoliate and stress trees. Since this is a naturally occurring pest, many forest health professionals believe the intensity and frequency of the damage will subside as populations naturally decline due to harsh winter conditions, an increase in predation, and/or the spread of a disease that kills the caterpillars.
For more information, contact Andrew Saunders, Athens-Clarke County Environmental Coordinator, at 706-613-3530 or firstname.lastname@example.org.
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