Experts report that this year's Eastern tent caterpillar egg hatch is about a week ahead of the past 10 years' average.
"By the end of March, all egg masses present should have hatched and larvae should be in the 1/2 to 3/4-inch range," said Lee Townsend, PhD, University of Kentucky (UK) College of Agriculture entomologist. "Small tents--approximately golf-ball sized--should be visible in cherry trees. This will be a good time to begin to assess activity and population size."
Townsend urged horse farms to check wild cherry and related trees for Eastern tent caterpillar activity to determine whether management is necessary. If control measures are needed to reduce numbers, property owners should take action before the caterpillars leave their trees.
"The small caterpillars will stay near the egg mass for a short time before moving to feed on expanding leaves," Townsend said.
"Eastern tent caterpillars grow and develop as long as the temperature is above 37 degrees; the warmer it is, the faster they will grow. Cold temperatures will slow them down, but the tent and the general cold hardiness of the species will keep them from being affected drastically, even if temperatures drop below freezing at night," he added.
Controlling Eastern tent caterpillars is vital to area horse farms, as UK research results indicate the caterpillars caused outbreaks of mare reproductive loss syndrome, which can cause late-term foal losses, early- and late-term fetal losses, and weak foals.
During the 2001-2002 MRLS outbreak, an estimated 30% of that year’s Thoroughbred foal crop was lost. The state suffered an economic loss of approximately $336 million in all horse breeds.
UK researchers conducted epidemiological and field studies that demonstrated MRLS was associated with unprecedented Eastern tent caterpillar populations on Kentucky horse farms. Studies since the 2001-2002 outbreak have subsequently revealed that horses will inadvertently eat the caterpillars and that the caterpillar hairs embed into the horses’ alimentary tract lining. Once that protective barrier is breached, normal alimentary tract bacteria might gain access to and reproduce in sites with reduced immunity, such as the fetus and placenta in pregnant mares. Fetal death from these alimentary tract bacteria is the hallmark of MRLS.
UK entomologists recommend that unless horse farm managers have been aggressive in managing Eastern tent caterpillars or removing host trees, they should keep pregnant mares out of pastures bordered by cherry trees for the next several weeks.
Townsend offered the following recommendations for controlling moderate to large caterpillar populations if horses cannot be moved to avoid possible exposure:
"Foliar sprays for caterpillar control can be made when tents are about the size of a baseball. Another option is the injection of trees with a systemic insecticide by commercial pesticide applicators or arborists. Regardless of the treatment used, it is important to revisit the sites in about five days to assess caterpillar activity," he said.
Holly Wiemers, MA, is communications director for UK Ag Equine Programs.