Scouting Alfalfa for Potato Leafhoppers: When and How

Mid-summer means potato leafhopper season is upon us. Many farmers question how to judge when leafhoppers have reached threshold and when spraying an insecticide is a wise choice. Here are some tips to help you in scouting your fields and arriving at a decision.

Scouting should begin five to seven days after the first cutting is taken from the field and should continue on a weekly basis (or bi-weekly if population counts reach close to threshold on a particular day). Check for stunting in the plants, yellowing of the leaves in a v-shaped pattern beginning at the leaf tip, as well as a “hopper burn” or red edge found on the leaf. This red burn can be easily confused with a Boron deficiency. However, finding the insect can confirm the cause.

The easiest way to scout for these insects is to use a small sweep net. Walk a W-shaped pattern in the field, and take sweep samples at five randomly selected areas. Leafhopper infestations generally begin on the edges of the field so be sure to include these areas in your checks.

To correctly sweep, test each of your five areas following these steps:

• Swing the sweep net in a 180-degree arc so the net rim strikes the top 6 to 8 inches of growth. Each 180-degree arc is one “sweep.”
• Take a sweep from right to left, walk a step, take another sweep from left to right, and so on.
• After taking five sweeps, quickly close the net and count the number of leafhoppers.
• Divide this number by five to get the average, and record these averages for each of the five areas in the field.
• If alfalfa is two or more weeks from harvest, consider applying treatments when leafhopper counts reach five leafhoppers/ sweep (adults and nymphs).
• For fields scheduled to be harvested in 10 days to 2 weeks, consider treating if hopper counts reach 10 leafhoppers/ sweep.

If you’re looking for another solution to help boost yields in your alfalfa fields, ask your Latham representative about the company’s new hybrid alfalfa lineup. Latham Hi-Tech Forage hybrid alfalfa is shown to outperform conventional varieties by 10-15%. More information about hybrid alfalfa is also available on our website.