At least seven species of blister beetles may be found in Kansas alfalfa. Beetles may be present in all cuttings of hay, but commonly occur in the second, third and fourth cuttings. Three-striped, grey and black species are all common and may occur as mixed-species swarms. Large aggregations may occur, but are typically transient. Avoid working fields with heavy equipment when aggregations are present.
The threestriped blister beetle, Epicauta lemniscata, contains especially high levels of cantharadin, which is toxic to horses.
The ashgray blister beetle, Epicauta fabricii, shown here on a curcurbit flower, often aggregates on blooming puncturevine.
The black blister beetle, Epicauta pennsylvanica, is attracted to many wild flowers, especially composites.
Foliar damage to alfalfa usually occurs in midsummer when fields may host large aggregations that can damage blossoms and leaves. Horses have an adverse and sometimes fatal reaction when fed hay containing crushed blister beetles. Chances of having blister beetles in hay can be reduced by avoiding the use of conditioners, crimpers, or crushers on the mid-June through September cuttings or by simply not using these cuttings as horse feed. However, there are no practices that can eliminate the possibility of hay being infested with blister beetles.
Kansas studies have documented blister beetle mortality during sickle-bar mowing where tractors drive over the blister beetles, crushing them into the hay. In these trials, the equipment that caused the least blister beetle mortality was a self-propelled swather (mower/windrower combination) that had the crimper rollers removed so that unconditioned hay was delivered into a windrow straddled by the unit’s wide-set wheels. Virtually no crushing of the hay and blister beetles occurred. Live blister beetles left the hay before it was baled. Even this unit could incorporate beetles into the hay at the ends of the field where tires crossed the windrows while turning, killing many beetles.
Avoid using hay from the ends of the fields for horse feed. Research has confirmed that dead blister beetles on the ground can be reincorporated into swathed hay following wheel traffic during raking and baling. It is important to avoid killing blister beetles in alfalfa fields. This means being vigilant for beetles when fields are being worked and keeping heavy equipment out of the field when aggregations are present - these will often disperse naturally within a day or two.
More information on blister beetles can be found in KSRE publication MF-959, Blister Beetles in Alfalfa.
Page last updated 10/29/2013 by J.P. Michaud.