Horn Fly Populations at the Hill Farm Research Station

As part of an long-term research project, the number of horn flies are counted weekly on several groups of cattle at the Hill Farm each fly season (typically May to October).  These trials are a joint effort between Dr. Sid DeRouen of the Hill Farm and Dr. Lane Foil of the Department of Entomology.

The numbers below are presented to allow producers to determine when fly numbers become large enough to begin to consider whether control measures should be used.  Fly populations in excess of 200 flies per animal have been found to supress animal performance.  Proper rotation of the type of insecticides (i.e., organophosphate, synthetic pyrethroid) is advised so as to limit the level of horn fly resistance to these insecticides.  Your local county agent can provide suggestions on rotations.

Counts began the third week of May, 2001.  Each group was kept in separate pastures from the others.  The control group was not protected with any insecticide and as such would represent the greatest number of flies that were observed on the Hill Farm.  Horn fly populations were determined by counting the number of flies with the aid of binoculars between the hours of 6:00 to 9:00 a.m.  Treatments were applied to those groups in the first week of June.  The value for the treated groups is an average of all cattle exposed to one of several treatment insecticides.