We are starting to see populations of immature grasshoppers across the state. Stay tuned as I discuss how to evaluate your alfalfa fields and potential control options.
Grasshoppers can be damaging in high numbers to our alfalfa and hay fields. And they will only get worse as the summer continues. You may need control in your field.
Control begins with scouting to determine if insecticides are economically useful. 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 5 grasshoppers per square yard or 15 grasshoppers per square yard in field margins, insecticides probably can be worthwhile. New fields planted in late August are very susceptible to grasshopper feeding and treatment is probably needed if the grasshopper population is just half this level.
Around many fields, grasshoppers have just started moving in from the field margins. Treating just the outside 150 feet, probably is sufficient in these situations. However, if the entire field is already infested, it usually is best to first harvest the alfalfa and then apply insecticide to protect the regrowth. There are several insecticides labeled for use on alfalfa.
To reduce the cost and amount of insecticide used when treating an entire field, harvest the alfalfa but leave several small, uncut strips across the field. The remaining grasshoppers will quickly congregate in these strips, enabling you to treat just these smaller areas.
Please be especially careful to avoid injuring bee and other important pollinating insects when using insecticides and carefully read and follow all label directions. Some precautions you can take to protect bees include time of day when spraying, using less toxic insecticides, and avoiding areas with blooming plants.
If you have many grasshoppers in your alfalfa, control them soon. As they grow larger, they’ll only get worse.