Most extension field specialists in crops report that potato leafhoppers are extremely abundant and are causing serious hopperburn to alfalfa. When fields turn yellow because of potato leafhopper injury, it is an obvious sign that the field is not being managed to prevent damage from this pest.
Potato leafhoppers damage alfalfa in several ways: losses in hay tonnage, delayed regrowth possibly causing the loss of a cutting, reduced viability and survivability of the stand during the winter, and increased weed growth (see photo). If you can see yellow hopperburn in a field, you also can expect to see some of these problems to occur in that field.
Fields should be scouted on a weekly schedule for potato leafhoppers. This may be even more critical this year because of their abundance. When the second cutting of alfalfa occurs this month, adult leafhoppers will hopscotch among neighboring fields. The regrowth for the third cutting must be scouted carefully. Large populations of leafhoppers migrating from a cut field to the new regrowth of an adjacent field can be very damaging.
Begin checking the regrowth after the cutting and continue every 5-7 days. Do not wait for hopperburn to appear on leaves before scouting. Use a sweep net and take 20 sweeps in 5 different areas of the field. Consider an insecticide application if the number of leafhoppers exceeds the following thresholds:
- if hay is less than 10 inches tall, consider spraying if you collect more than 0.1 leafhopper per sweep for each inch of plant height (for example, if the hay is 4 inches tall, spray if the average number exceeds 0.4 leafhopper per sweep), or
- if the hay is taller than 10 inches, 2 or more leafhoppers is the acceptable threshold.
Some of the insecticides labeled for leafhoppers are listed below. The minimum label rate and the preharvest interval are given. Always read and follow label directions.
Insecticides labeled for leafhoppers.
This article originally appeared on pages 135-136 of the IC-478(17) -- July 14, 1997 issue.