While many believe that the presence of a single beetle in a bale of hay poses a health hazard to a horse, the risk is not quite that great and the risk varies with the type of blister beetle. Although cantharidin is extremely toxic to horses, blister beetles are small and individuals do not contain a lethal dose. Dr. John Capinera measured the cantharidin levels in several blister beetle species and estimated their relative risk to horses of different body weights. Clearly, different blister beetle species poses different risks to horses. These differences should be taken into account in management decisions.
Cultural practices involve timing of cutting and modification of harvest equipment.
Since blister beetles are attracted to flowers, cutting the crop prior to bloom should reduce their presence in hay. Control of flowering weeds is also important. The choice of harvest equipment giving the beetles the best chance of survival is also important. Recent research at Kansas State University has shown that self-propelled swathers without conditioning rollers but with windrowing attachments are safer than mower conditioners and sicklebar mowers. Even with the conditionerless swather avoid hay from the ends of the fields where beetles may be crushed by tires as the swather is turned around.