Start Scouting for Potato Leafhoppers in Alfalfa
Potato leafhopper (Photo by Jim Kalisch)
Potato leafhoppers have the potential to cause economic injury to alfalfa every year in Nebraska, usually to second or third cutting. They do not overwinter in Nebraska, but are brought in on southerly winds. A good time to check fields is right after storm fronts move through an area.
Given the very active weather patterns we have been experiencing, I went on an alfalfa scouting tour in northeast Nebraska and observed fields with 0.25 to 2 potato leafhoppers per sweep. This level could merit treatment for some alfalfa fields. If you have not scouted your alfalfa lately, now is a good time to begin.
These small (1/8 inch long), bright green, wedge-shaped insects can cause severe damage to alfalfa by injecting a toxin into the plant as they feed. This feeding results in a distinctive yellow or purple triangle shape at the leaf tip. First year, spring-planted alfalfa fields are particularly attractive to and vulnerable to potato leafhoppers, as are fields planted last year. In older fields, these insects are usually a problem on second and third cuttings.
Newly developed, resistant alfalfa varieties provide fairly good protection from potato leafhoppers; however, seedling alfalfa may still be damaged. All fields should still be scouted, as large numbers of leafhoppers can cause a problem, even in resistant-variety fields.
Treatment Thresholds and Insecticides
Treatment decisions are based on numbers captured by a sweep net. (A sweep net is the only reliable way to scout for potato leafhoppers.) See Tables 1-3 for decision-making help. Note that there do not have to be many to cause a problem.
Many insecticides are registered for control, and all will provide good results when applied properly. Commonly used insecticides include Mustang, Warrior, Baythroid, and Lorsban, or products with the same active ingredients.
For a list of registered alfalfa insecticides, see the Insecticide Section in the UNL Extension EC130, 2014 Guide for Weed Management with Insecticide and Fungicide Information.
Tom Hunt
Extension Entomologist, Haskell Ag Lab, Concord
Robert Wright
Extension Entomologist, Lincoln
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Table 1. Dynamic treatment thresholds for potato leafhoppers (average number per sweep) on alfalfa that is 1 to 4 inches tall. |
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Value of hay (per ton) |
Cost of insecticide application (per acre) |
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$8 |
$10 |
$12 |
$14 |
$16 |
$20 |
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$ 60 |
0.4 |
0.5 |
0.6 |
0.7 |
0.8 |
1.0 |
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$ 80 |
0.3 |
0.4 |
0.5 |
0.5 |
0.6 |
0.75 |
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$100 |
0.25 |
0.3 |
0.4 |
0.4 |
0.5 |
0.6 |
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$120 |
0.2 |
0.25 |
0.3 |
0.35 |
0.4 |
0.5 |
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$140 |
0.2 |
0.2 |
0.25 |
0.3 |
0.3 |
0.4 |
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$160 |
0.15 |
0.2 |
0.3 |
0.3 |
0.3 |
0.4 |
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Table 2. Dynamic treatment thresholds for potato leafhoppers (average number per sweep) on alfalfa that is 4 to 8 inches tall. |
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Value of hay (per ton) |
Cost of insecticide application (per acre) |
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$8 |
$10 |
$12 |
$14 |
$16 |
$20 |
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$ 60 |
0.7 |
0.8 |
1.0 |
1.0 |
1.3 |
1.7 |
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$ 80 |
0.6 |
0.6 |
0.75 |
0.9 |
1.0 |
1.3 |
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$100 |
0.4 |
0.5 |
0.6 |
0.7 |
0.8 |
1.0 |
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$120 |
0.3 |
0.4 |
0.5 |
0.6 |
0.7 |
0.8 |
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$140 |
0.3 |
0.35 |
0.4 |
0.5 |
0.6 |
0.7 |
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$160 |
0.25 |
0.3 |
0.4 |
0.4 |
0.5 |
0.6 |
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Table 3. Dynamic treatment thresholds for potato leafhoppers (average number per sweep) on alfalfa that is 8 to 12 inches tall. |
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Value of hay (per ton) |
Cost of insecticide application (per acre) |
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$8 |
$10 |
$12 |
$14 |
$16 |
$20 |
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$ 60 |
2.0 |
2.4 |
2.8 |
3.0 |
3.9 |
5.0 |
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$ 80 |
1.8 |
1.9 |
2.2 |
2.7 |
3.0 |
4.0 |
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$100 |
1.2 |
1.5 |
1.8 |
2.1 |
2.4 |
3.0 |
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$120 |
0.9 |
1.2 |
1.5 |
1.8 |
2.1 |
2.4 |
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$140 |
0.9 |
1.0 |
1.2 |
1.5 |
1.8 |
2.0 |
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$160 |
0.8 |
0.9 |
1.0 |
1.2 |
1.5 |
1.8 |
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