Blister Beetles Pose Risk to Summer Alfalfa Harvest

By Scout Nelson

Frequent rains across many areas have helped increase alfalfa growth this summer, allowing growers to collect second or even third cuttings. While this is good for production, it brings a higher chance of encountering blister beetles, especially later in the growing season. These beetles can pose serious risks to livestock health.

Blister beetles feed on alfalfa leaves and blossoms and contain a toxic chemical called cantharidin. This chemical can cause blisters on skin and becomes dangerous when animals eat infested hay. If livestock consume enough beetles, it can lead to health problems like mouth sores, stomach issues, kidney damage, and even death.

Farmers are advised to scout alfalfa fields before every cutting. This is especially important during second or later cuttings, as beetles are more common in mid to late summer. Fields with high grasshopper activity the previous year are also more likely to have blister beetles, since their young feed on grasshopper eggs.

Using insecticides is not recommended, as they kill the beetles but do not remove their bodies from the hay. Dead beetles are still toxic, and chemical spraying might result in more beetles in each bale.

Instead, farmers should cut alfalfa before it reaches full bloom, since the beetles are drawn to the blossoms. After mowing, the crop should dry fully before raking or baling. This gives beetles time to leave the plants naturally.

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