University of Vermont

Potato Leafhopper in Alfalfa Potato Leafhoppers in Alfalfa

Sid Bosworth, Extension Associate Professor, Department of Plant and Soil Science, University of Vermont

If you've ever seen alfalfa with significant yellowing and stunting in mid-summer, chances are you've seen potato leafhopper damage (referred to as “hopperburn”). But since they overwinter in the south and migrate annually, each year varies dramatically from very few problems to occasional years like we had in 1997. The adults will usually show up in New England sometime in June and are most likely to be found first in Connecticut, Massachusetts, and southern Vermont. They often are not a problem in northern New England except for that occasional year.

Potato leafhoppers are piercing-sucking insects. They pierce the leaf midrib and suck out sap. In the process, they secrete a substance that disrupts the vascular system of the plant causing the yellowing of the leaf tips and the stunting of the plants. Young seedlings are particularly susceptible to this type of injury and should be monitored closely.

At a high enough population (critical threshold), potato leafhoppers can reduce yield, reduce protein and weaken the stand to the point that there is a higher risk of winter kill. The effect can even carryover into the next year. Research from the mid-West, where this insect is more of a problem, found a production increase of ½ ton hay per acre on first cutting when leafhoppers had been controlled the previous year.

It is important to find this insect before it becomes a problem. By the time you see yellow plants, it is too late. This very small (only 1/8 inch in length), yellowish-green colored, wedge shaped insect has long hind legs that allow it to hop like a grasshopper [image]. The adults can also fly very quickly. Nymphs resemble the adults but are wingless and have a more pronounced yellow color. They characteristically move sideways at a rapid pace.

You will usually find them on the underside of leaves, but they move quickly away as you walk through the field. The best way to catch them and determine a population is with a standard 15 inch insect sweep net. By taking five sets of 10 sweeps throughout the field, you can determine a population per sweep. The best approach as walking is to swing the net into the tops of the alfalfa in a pendulum motion. Each pass counts as a sweep. Take 10 consecutive sweeps and carefully count leafhoppers. Depending on plant height, a critical threshold can be 0.2 leafhoppers per sweep (when plants are less than 3 inches tall) to 2 per sweep (when plants are 11 - 14 inches). The following are recommended thresholds for determining an economic treatment.

Action Thresholds of Potato Leafhopper in Alfalfa (Cornell University)

Average stem height
Leafhoppers/10 sweeps
< 3 inches (new seedings) 
3 to 7 inches 
8 to 10 inches 
11 to 14 inches 
15 inches or above 
20 or more* 

*If leafhoppers exceed 20 per 10 sweeps and if regrowth is within
1 week of harvest, no action is needed. If not, consider a
short-residue insecticide.

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Last modified May 26 2004 01:29 PM

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