Published April, 2011

Eastern tent caterpillars (ETC) were identified as the cause of foal loss during the mare reproductive loss syndrome outbreaks in 1999-2001. Over the last three years, ETC populations in Central Kentucky have been increasing gradually but there are still wide differences in numbers from one area to another. This is normal for the caterpillar's dynamics.

ETC larvae should be approximately 0.5 to 0.75 inches in size in Central Kentucky. This time of year the caterpillars are beginning to move from 2- to 3-inch-long tents near their egg mass to larger masses at major branch forks.

Most tents should be baseball- to softball-size, making them easy to see in trees, particularly on sunny days. Consequently, if pregnant mares are present in pastures, now is the time to check for tents along pasture and paddock tree lines that contain wild cherry trees. Any management of the caterpillars should be done while they are together in tents. It is difficult to provide effective control once the ETCs are fully grown and have dispersed from host trees.

One management option is to move pregnant mares away from identifiable ETC concentrations. If this is not practical, then physical removal of tents or spot treatment with insecticides is an alternative approach.

ETCs were identified as the cause of foal loss during the Mare Reproductive Loss Syndrome (MRLS) outbreak in 1999-2001.

Lee Townsend, PhD, a University of Kentucky College of Agriculture entomologist, provided this information.