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March 14, 2003

Eastern Tent Caterpillar Management on Horse Farms - 2003

By Lee Townsend, Extension Entomologist
Department of Entomology
University of Kentucky College of Agriculture

Overwintering Populations Appear Low

Careful examination of many central Kentucky wild cherry trees over the past few weeks points to a very low population of eastern tent caterpillars (ETC) this spring as compared to recent years. Relatively small numbers of “fresh” egg masses can be found at most sites but usually only after a thorough search. As you would expect, there is some site-to-site variation but all still remain in the “low” category. This year appears to be a situation where tents will be few and scattered. Careful watching and directed spot sprays can be used to control the caterpillars in cases where mares will be pastured near cherry trees.

No Preventive Control

There is no preventive approach to ETC control prior to egg hatch. If insecticides are to be used, either as foliar sprays or injections, they must be applied after egg hatch is complete and small tents are visible in trees.

Spring 2003 Weather Delays Egg Hatch

Cold weather this spring is delaying both cherry bud break and ETC egg hatch compared to last year. No hatch has been seen as of 13 March 2003. However, a series of warm days will push things along rapidly. Forsythia bloom is a phenological event that can be used to determine when to scout cherry trees. Egg hatch of ETC coincides with about 50% bloom of Forsythia so FULL BLOOM is the right time to be scouting trees for the small tents. Don’t spray or inject until small tents are seen.

Duration of Egg Hatch

University of Kentucky Entomology research from last spring showed that ETC egg hatch occurred over almost three weeks. Not even all the eggs in a single mass hatched at the same time. Newly hatched caterpillars tend to remain on or very near the egg mass for several days and are not significantly affected by cold temperatures or even hard rains.

ETC Control Program

There are 4 elements of an ETC control program:

An insecticide application to control ETC should be made after egg hatch has occurred and when small (at least baseball-sized) tents are visible in the trees. The spray should be applied after egg hatch and directed to foliage within about 3 feet of the nest, or where caterpillars are feeding. Bt- based insecticides must be eaten by the caterpillars to work so they need to be applied to expanded foliage, not to the nest.

What control alternatives are available?

Foliar Sprays

Bacillus thuringiensis - Bt based insecticides (Dipel, etc.) are derived from a toxin produced by a soil microbe. They are specific to caterpillars, especially small ones, by disrupting the digestive tract. Poisoned caterpillars generally stop feeding within hours after feeding on treated foliage but may not die for several days. It will control small caterpillars but is less effective as the larvae grow larger. Bt products are broken down by sunlight and the effective residual life on foliage appears to be about 3 to 5 days. Bt is essentially nontoxic in the environment and labels do not contain grazing or harvest restrictions.

Sevin (carbaryl) SL or WP. Sevin is a carbamate insecticide that attacks the nervous system. It can act on caterpillars as both a contact and a stomach poison. Carbaryl can be effective as a direct spray on exposed caterpillars. Labels of turf and ornamental formulations of carbaryl do not limit grazing or harvest but agricultural product labels for alfalfa and pastures contain a 14 day grazing / harvest wait.

Talstar Lawn & Tree Flowable, Talstar Nursery Flowable (bifenthrin), and certain other pyrethroids work well for ETC control. Talstar provided rapid kill and the residues are effective on leaves for about 7 days. These products work on the nervous system of the caterpillar and act as stomach and contact poisons. Many pyrethroids are Restricted Use pesticides because of potential environmental harm, especially to aquatic organisms.


A trunk injection of Inject A Cide B (bidrin), applied when a foliar spray would be used, has given excellent control of ETC in large trees. The insecticide is carried in sap to the leaves and kills the caterpillars as they feed. It is most effective against small to medium-sized caterpillars but will not work as well against large ones (2" inches or longer)

What about spraying pastures?

Several insecticides, such as Sevin (carbaryl) or Bt products, are labeled for application to pastures to control several caterpillar pests. There is NO benefit to spraying pasture grasses to kill wandering ETC.

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