Scouting for and Treating Potato Leafhoppers - UNL CropWatch;, July 8, 2011
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July 7, 2011
Potato leafhoppers have the potential to damage alfalfa in Nebraska every year. This is generally a second and third cutting pest that has been common in eastern Nebraska recently. It doesn’t overwinter in Nebraska but rather is brought in on southerly winds each spring.
Low numbers of potato leafhoppers have now been observed in southeastern and south central Nebraska, so it is time to begin scouting.
These small (1/8 inch long), bright green, wedge-shaped insects may 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, but alfalfa in the seedling stage may still be damaged. All fields should still be scouted, as large numbers of leafhoppers may still 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.) To obtain reliable estimates of potato leafhopper abundance, at least 25 sweeps should be taken from each of four locations in a field. A sweep is defined as one 180° swing of the sweep net across the foliage. See Tables 1-3 for decision-making help. Note that there do not have to be many leafhoppers 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. Refer to the http://entomology.unl.edu/instabls/alfalfa_piercing_sucking.shtml for a list of suggested insecticides.
More Information
For information on potato leafhopper biology and management, see Potato Leafhopper Management in Alfalfa, UNL NebGuide G1136.
Keith Jarvi
Extension Educator in Dakota, Dixon, and Thurston Counties
Tom Hunt
Extension Entomologist, Haskell Agricultural Laboratory, 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 |
|
$100 |
0.25 |
0.3 |
0.4 |
0.4 |
0.5 |
0.6 |
|
$120 |
0.2 |
0.25 |
0.3 |
0.35 |
0.4 |
0.5 |
|
$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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|
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$8 |
$10 |
$12 |
$14 |
$16 |
$20 |
|
$ 60 |
0.7 |
0.8 |
1.0 |
1.0 |
1.3 |
1.7 |
|
$ 80 |
0.6 |
0.6 |
0.75 |
0.9 |
1.0 |
1.3 |
|
$100 |
0.4 |
0.5 |
0.6 |
0.7 |
0.8 |
1.0 |
|
$120 |
0.3 |
0.4 |
0.5 |
0.6 |
0.7 |
0.8 |
|
$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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