A Strategy for Managing Grasshoppers in Alfalfa

July 31, 2015

There have been reports of high numbers of grasshoppers in alfalfa, making it a good to evaluate control options.

Control begins with scouting. Exact economic thresholds can't be determined because of variables like value of the alfalfa and growth stage of both alfalfa and grasshopper.  Still, if the grasshopper population in an established field is higher than five grasshoppers per square yard throughout the field or 15 hoppers per square yard in field margins, insecticides will probably be worthwhile.  Newly planted fields may need treatment if the grasshopper population is just half this level.

Around many alfalfa fields, grasshoppers have just started moving in from the field margins.  Treating just the outside 150 feet or so may be sufficient in these situations.  However, if the entire field is already infested, it is usually best to harvest the alfalfa and then apply insecticide to protect the regrowth.

To reduce the cost and amount of insecticide used when treating an entire field, harvest alfalfa but leave several small, uncut strips across the field.  The remaining grasshoppers will quickly congregate in these strips, enabling you to just treat these smaller areas.  Reduced area/agent treatments also have proven effective for alfalfa.

Carefully read and follow all label directions and be especially careful to avoid injuring bee and other important pollinating insects.

Bruce Anderson
Extension Forage Specialist