Leafhoppers can stunt alfalfa

Potato leafhoppers can now be found in alfalfa fields across the state. Now is the time to scout alfalfa on a weekly basis for this pest. If leafhoppers are abundant, there will be losses in yield. The most obvious signs of injury are the reduced stem height and yellowing of the leaves, which is called hopperburn. Damaged plants are severely stunted, often to the point of providing opportunities for increased weed growth. Losses in harvest tonnage can be attributed to this stem-shortening response.

Adult and nymphal potato leafhopper.
Severe hopperburn on alfalfa.

Potato leafhopper damage also can delay the maturity of the crop. This delay can be extreme enough to eliminate a final harvest in the fall.

To scout for leafhoppers, begin checking the regrowth after the first cutting and continue every 5-7 days. Do not wait for hopperburn to appear on the 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:

  1. if the 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 8 inches tall, spray only if the average number exceeds 0.8 leafhopper per sweep.
  2. 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 preharvest interval are given. Always read and follow label directions.

Insecticides labeled for leafhoppers.

Insecticide Minimum rate Preharvest interval
Ambush* 3.2 ounces 0 days
Cygon 400 0.5 pint 10 days
Furadan 4F* 1 pint 14 days
Lorsban 4E 1 pint 14 days
Penncap-M* 2 pints 15 days
Pounce 3.2EC* 4 ounces 0 days
Sevin XLR+ 2 pints 7 days

*Restricted-use insecticide.

This article originally appeared on pages 108-109 of the IC-478(14) -- June 23, 1997 issue.

Updated 06/22/1997 - 1:00pm