By JORDAN STRICKLER

Kentucky Correspondent

LEXINGTON, Ky. — Eastern tent caterpillars (ETC), historically dangerous to Kentucky’s equine industry, are beginning their yearly hatching. The larvae are among the first pests to become active in the spring and are well-equipped to cope with the state’s erratic temperature swings.

Mare Reproductive Loss Syndrome, an event that occurred from 1999-2001, was traced back to the caterpillar. The epidemic ended up causing 20-30 percent of Kentucky's pregnant mares to suffer abortions and had a nationwide financial impact of $336 million. Consumption of the ETC by mares caused late-term foal losses, early- and late-term fetal losses, and weak foals.

Researchers from the University of Kentucky (UK) conducted studies that revealed horses will inadvertently eat the caterpillars, and their hairs embed into the lining of the horse’s alimentary tract. Once that protective barrier is breached, normal alimentary tract bacteria may gain access to and reproduce in sites with reduced immunity, such as the fetus and placenta.

However, preventative measures to keep the threat minimized are relatively simple. If practical, farm managers should move pregnant mares from areas where wild cherry trees are abundant and where small ornamental trees are planted to minimize the chance of caterpillar exposure.

The threat is greatest when the mature caterpillars leave trees and wander to find places to pupate and transform to the moth stage. According to UK’s entomology researchers, egg hatch occurs over several weeks in early spring, which increases the chance for survival in case of late freezes.

The caterpillars grow and develop when the temperature is above 37 degrees F. ETC’s food trees of choice are wild cherry, apple, and crabapple, but they may also be found on hawthorn, maple, cherry, peach, pear, and plum.

“Managing ETC in small ornamental trees, such as flowering crabapples, is easy,” says Daniel Potter, professor of entomology at UK. “Just wear a pair of grocery store plastic bags like mittens, climb a stepladder, pull out the tents, turn the bags inside out to ‘bag’ the caterpillars, and stomp them.

“Pruning out nests in ornamental trees sounds great, but in reality, by the time they are noticed, they’re often in branch crotches where pruning will compromise the symmetry of the tree.”

According to Potter, ETC management around horse farm paddocks comes down to keeping pregnant mares away from infested trees and either removing or not planting preferred host trees near paddocks.

In addition to those preventive measures, controlling the caterpillars with insecticides may be warranted in some settings. That may require treating tall trees that are difficult to spray.

Farm managers can use any one of several biorational insecticides registered for use on shade trees as needed. These types of insecticides are relatively nontoxic to humans. Spot treatments to the tents and the foliage around them can be applied according to label directions, which vary by product.

“Except for Bacillus thuringiensis (or Bt), which is not all that effective once the ETC are about half-grown, the only spray product I know of that controls ETC and is bee-compatible is Acelepryn (chlorantraniliprole),” Potter said. “That is available in a formulation used mainly by professional grounds managers and arborists, but has not yet found its way into homeowner spray products.”