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Blister Beetle Control in Alfalfa
Blister beetles are infrequent pests of forage crops including alfalfa. Their populations increase during and after grasshopper outbreaks (the larvae are grasshopper egg predators). These insects usually cause limited plant damage, but when ingested by livestock, especially horses, sickness or death can result. Horses are most susceptible to the toxin (cantharidin), however, sheep and beef cattle can also experience symptoms to a lesser degree. Little is known about the effect of the toxin on lactating dairy cows.
Management strategies for reducing the number of blister beetles in hay include:
(1) control flowering weeds in the field and cut alfalfa prior to bloom,
(2) check hay prior to cutting and if beetles are present, wait a few days until beetles move and then cut hay,
(3) avoid using hay conditioners or crimpers which may crush and kill beetles in the hay, and
(4) chemical control.
If beetles need to be controlled prior to harvest, malathion and carbaryl will be effective. Malathion does not have any harvest restrictions while fields treated with carbaryl cannot be harvested for 3 days.
For more information see the Field Crop Insect Management Guide at http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm
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