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Scouting alfalfa for potato leafhoppers

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Following some issues with aphids and alfalfa weevil prior to first cutting, we now are moving on to a second major insect pest in alfalfa prior to second cutting and beyond, the potato leafhopper.

Last year on June 15, we found potato leafhoppers using a sweep net during a site visit in Gage County on June 15. Though I have not had any reports yet this year, it is not too early to start scouting your alfalfa. Potato leafhoppers can cause tonnage and significant economic losses, so good scouting and timely management is justified.

Potato leafhoppers are tiny, yellowish-green, wedge-shaped insects about 1/8 of an inch long. There are five nymph stages with the first three stages crawling on the plant but hopping around the plant at the 4th and 5th stages as a nymph when disturbed. Adults migrate via wind from the southern U.S. into Nebraska late spring and then disperse locally during the summer. In addition to alfalfa, potato leafhoppers can reproduce on numerous other host plants. Potato leafhoppers populations can increase rapidly since females can deposit over 200 eggs. Egg and nymph development takes about 10 days and there can be overlapping generations. As a result, populations in alfalfa fields can double in 10 days.

Early plant damage symptoms from potato leafhoppers includes V-shaped yellow or purple areas on leaf tips caused by the toxins injected into the plant as it sucks out alfalfa juices. Entire plants can turn yellow and stop growth under more severe damage. New seedings from last fall or this spring are particularly attractive to potato leafhoppers.

Potato leafhopper treatment decisions are based on utilizing a sweep net and is the only reliable way to scout for this pest. If you do not own a sweep net, you can borrow/check out one from our Extension offices in Beatrice, Fairbury, and Wilber. Depending on the alfalfa height/stage, value of hay, and insecticide/application cost, less than 1 to as much as 5 potato leafhoppers per sweep could warrant an insecticide application and at current hay prices the threshold is less than 1 to 2 per sweep. View three dynamic treatment threshold tables from a CropWatch article written by Bob Wright, Extension Entomologist, on my local website at croptechcafe.org/alfalfa.

Management options include either no change to your planned cutting, early cutting alfalfa, spraying an insecticide, and combinations of those. Cutting alfalfa fields disrupts the life cycle and sets back the local population. Cutting an alfalfa field removes the eggs in hay and the nymphs die from desiccation or starvation. However, adults can survive by flying to nearby areas with host plants. Adults then move back into fields as the alfalfa regrows to feed and lay eggs, thus repopulating the field. That is why

regular scouting for potato leafhoppers is important all summer on a weekly basis. If applied correctly, potato leafhoppers can easily be controlled with insecticides. Insecticides containing chlorpyrifos (e.g. Lorsban) can no longer be applied due to an EPA rule that started on March 1, 2022. There are numerous insecticide options, and we have a very comprehensive list in our 2022 Guide for Weed, Disease, and Insect Management in Nebraska available for sale online at extensionpubs.unl.edu.

For more information about potato leafhoppers other agronomic resources from Nebraska Extension, contact me at nathan.mueller@unl.edu or 402-821-1722. Know your crop, know your tech, know your bottom line.

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