Leafhopper season has arrived for 2018

Insecticide resistance in insects places emphasis on scouting for harmful insects.

June 28, 2018 - Author:

Potato leafhopper
Potato leafhopper "hopperburn." Photo by Phil Kaatz, MSU Extension.

Alfalfa producers that have experienced dry weather during the month of June should be on the lookout for potato leafhopper (PLH) damage in their fields. New seedings and field with regrowth less than three inches are particularly susceptible to damage from the pest. The recommendation from Michigan State University Extension is to utilize an Integrated Pest Management approach to dealing with this insect.

MSU Entomologist Chris DiFonzo says, “Potato leafhopper is the most important insect pest of alfalfa and dry beans in Michigan.” Potato leafhoppers feed by sucking sap out of plants, injecting saliva as they feed. But unlike most other leafhoppers, potato leafhopper’s saliva is toxic and results in abnormal cell growth and blockage of fluid transport in the leaf. The visual symptom in many plants is a characteristic yellowing called “hopperburn.” (See photo) Both nymphs (immatures) and adults cause this damage. Because of the damage, reduction of yield, forage quality, plant vigor and winter-hardiness will occur.

In alfalfa, sample using a sweep net and treat based on a combination of potato leafhopper number per sweep and average plant height. Regrowth (plants under three inches) is particularly vulnerable to potato leafhopper damage. As the crop grows, it can handle a greater number of leafhoppers.

The threshold values are:

  • Under 3-inch alfalfa [regrowth]: 0.2 adults per sweep = 20 per 100 sweeps
  • 3 – 8 inch alfalfa: 0.5 adults per sweep = 50 per 100 sweeps
  • 8 – 12 inch alfalfa: 1 adult and/or nymphs per sweep = 100 per 100 sweeps
  • 12 – 14 inch alfalfa: 2 adults and/or nymphs per sweep = 200 per 100 sweeps

Although no issues have been reported with potato leafhopper resistance to insecticides, the number of insects showing pesticide resistance is growing across the United States. Pesticide resistance is described as the decreased susceptibility of a pest population to a pesticide that was previously effective at controlling the pest. Research shows that resistance problems have increased because pesticides are applied more frequently and at higher dosage rates.

For more information, contact Phil Kaatz at 810-667-0341 or email at kaatz@msu.edu.

Tags: leafhopper burn, msu extension, potato leafhopper

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