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Scout Alfalfa for Potato Leafhopppers

Damage in alfalfa is often most severe in new seedlings and in young regrowth. While potato leafhopper nymphs and adults suck juices from plant foliage, they inject a protein that blocks veins. This causes the edges to become yellow and puckered, with a characteristic yellow "V" shape beginning at the tip of the leaves.

When severe, the leaves appear burned, which is called "hopperburn". PLH can cause a 2%-3% reduction in the percentage of protein, in addition to reducing both the average height and yield. Border areas are usually affected first. Leafhoppers tend to come into soybean and edible bean fields after neighbouring alfalfa fields are cut. The symptoms of potato leafhopper are commonly confused with herbicide injury problems and nutrient deficiency. Most of the damage occurs from June to mid-August. High risk factors include hot, drier-than-normal seasons.

Scouting Technique

Take 20 sweeps from five areas of the field beginning in late June. Avoid field edges. Determine the average number of PLHs per sweep. Next, take 20 alfalfa stems at random and record the average plant height.

Potato Leafhopper Action Thresholds for Alfalfa

If populations exceed the action thresholds, an insecticide may be necessary. Refer to OMAFRA Publication 812, Field Crop Protection Guide, for insecticide information. It should be noted that spraying insecticides on alfalfa will also kill beneficial insects, the natural enemies of PLH, alfalfa weevil and lygus bug.

Hail damage occurred in some parts of the province recently and the following article from Bob Nielsen at Purdue University gives a good summary of the impacts of hail on the developing corn crop.