Poison Control: Spraying Insecticides on Pastures

During the optimal Eastern tent caterpillar (ETC) eradication period (when larvae are still in trees), Lee Townsend, PhD, extension entomologist at the University of Kentucky (UK), recommended a list of insecticides for horse owners and farm managers to use to keep ETC off their pastures. The talk about insecticides had some individuals asking which are safe to use, and which, if any, should be avoided.

Petra Ann Volmer, DVM, MS, Dipl. ABVT, Dipl. ABT, an assistant professor of toxicology and director of the veterinary toxicology residency program at the University of Illinois, says that most of the insecticides on UK's list are from the pyrethrin family. She thinks these are some of the safest insecticides because of their short environmental impact. This family includes Bifenthrin, Lambda-cyhalothrin, and Cyfluthrin, commonly used across the country for many purposes (such as fly repellent and roach control), but not registered for application to pastures. If used properly on fencerows or tree bases, they should not be a threat to grazing mares or foals.

Carbaryl (a carbamate insecticide) is also safe in Volmer's opinion. "Carbaryl is the material used in flea powder that is applied directly to cats and dogs," says Volmer. Carbaryl is labeled for application to pastures for insect control.

"The insecticide family you want to avoid is organophosphorus," says Volmer. "They tend to be more toxic to mammals than the pyrethrin family." UK did not recommend any organophosphorus insecticides.

As long as label instructions are followed, the only side effects that might affect people doing the application is a mild tingling sensation if the chemical contacts the skin. Volmer said basic precautions should be taken when applying insecticides, such as wearing gloves and goggles, not spraying when it's windy, and keeping animals out of the area until the spray has dried.

Results from lab tests on these insecticides have concerned some horse owners. In one study, Cyfluthrin caused weight loss, kidney inflammation, vomiting, and diarrhea when lab animals were chronically exposed. However, Townsend and Volmer agree that the lab testing is conducted over long periods of time with high doses targeted to the animal; these circumstances are unlikely to occur in the field.

Volmer says, "The testing is usually done by the companies producing the products to satisfy EPA regulations. The insecticide labels will list any major side effects."

The prime ETC eradication period for this year is now over, but these insecticides can be used for other insects. Remember to follow label directions, and consult your veterinarian if you are concerned with the possibility of negative effects on your horse's health. For Townsend's full list of recommendations on eradicating ETC, go to www.uky.edu/Agriculture/VetScience/mrls/ETC502.html.

About the Author

Sarah Adams, Editorial Intern

Sarah Adams was once an editorial intern for The Horse: Your Guide to Equine Health Care.

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