Are Blister Beetles in Your Hay?

Berni Kurz
Berni Kurz

We have had a few calls this summer with blister beetles being found in some hay fields. Blister beetles are attracted to a fairly common weed called horsenettle which is known by some as bullnettle. Legumes are also a favorite plant to eat by this insect and on top of the list is alfalfa followed by clovers. So, what is the big deal about blister beetles in a hay field? These beetles produce cantharadin, which is a potent toxin that causes severe irritation and necrosis of any mucus membranes that it comes in contact with.

Blister beetles tend to swarm when the hay or nearby weeds are in bloom. Mower-conditioners that cut and crimp the hay will trap dead beetles within the windrow or swat. These beetles retain their toxicity in dry hay. All classes of animals that eat forages may be affected; however, most cases have been reported in horses. Animals may become severely dehydrated and will usually die from kidney failure and shock. The intestines and urinary tract are severely damaged. Animals with blister beetle poisoning should have the hay removed from the diet. The hay should be destroyed because the toxicity does not lessen with time. If it is not too far advanced, animals can be treated for kidney failure and shock. The outcome, however, is usually not successful.

The risk of blister beetle toxicosis can be reduced by doing one thing. Drive through the hay field and observe plants that this beetle is attracted to right before you plan to cut the field. If you find beetles, you can cut around spots and follow up with spraying with an insecticide. If it's more than just spots, you will need to spray the entire field and delay cutting by a week.

So, are blister beetles in your hay crop? For more information on this beetle, call me at your County Extension office.

BERNI KURZ, COUNTY EXTENSION AGENT STAFF CHAIR, UNIVERSITY OF ARKANSAS DIVISION OF AGRICULTURE COOPERATIVE EXTENSION SERVICE.

General News on 07/22/2015