University of Nebraska-Lincoln Extension, Institute of Agriculture and Natural Resources

June 15, 2006

Potato leafhopper.
Alfalfa leaf showing potato leafhopper damage.

Potato leafhoppers damaging alfalfa

Potato leafhoppers have the potential to hurt alfalfa in Nebraska every year. This is generally a second and third cutting pest and has been common in Nebraska recently, particularly in the eastern third of the state. Southerly winds bring this insect into Nebraska, as is does not overwinter here. We have had reports of some damage, so it is time to begin scouting.

Potato leafhoppers are small (1/8 inch long), bright green, wedge shaped insects. As the name implies they will jump from the surface of the plant when disturbed, which makes it difficult to scout for them unless you have a sweep net. Immature leafhoppers are smaller, wingless and often scuttle crab-like across the leaf surface. Leafhoppers 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 tip of the leaf. Feeding can kill leaves, stunt plants and halt growth. 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 varieties will protect from potato leafhoppers fairly well, 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. Accurate counts are impossible without a net.

Treatment decisions are based on numbers captured by sweep net. Take 10 to 20 sweeps in several areas of the field and average the number per sweep. See Tables 1-3 for decision-making help. Note that there do not have to be many to cause a problem. Prices for alfalfa may be below those shown in the table but numbers can be adjusted accordingly. Remember when the value of a crop goes down, the number of insects it takes to justify a treatment goes up. A large number of insecticides are registered for control, and all with provide good results when applied properly. Refer to the UNL Department of Entomology Web site for potato leafhoppers for a list of suggested insecticides.

Keith Jarvi
Integrated Pest Management
Haskell Ag Lab, NEREC

Table 1. Dynamic treatment thresholds for potato leafhoppers (average number per sweep) on alfalfa that is 1 to 4 inches tall.
Value of hay (per ton)
Cost of insecticide application (per acre)
$ 60
$8
$10
$12
$14
$16
$20
$ 80
0.4
0.5
0.6
0.7
0.8
1.0
$100
0.3
0.4
0.5
0.5
0.6
0.75
$120
0.25
0.3
0.4
0.4
0.5
0.6
$140
0.2
0.2
0.25
0.3
0.3
0.4
$160
0.15
0.2
0.3
0.3
0.3
0.4 0
             
Table 2. Dynamic treatment thresholds for potato leafhoppers (average number per sweep) on alfalfa that is 4 to 8 inches tall.
Value of hay (per ton)
Cost of insecticide application (per acre)
 
$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
$160
0.25
0.3
0.4
0.4
0.5
0.6
             
Table 3. Dynamic treatment thresholds for potato leafhoppers (average number per sweep) on alfalfa that is 8 to 12 inches tall.
Value of hay (per ton)
Cost of insecticide application (per acre)
 
$8
$10
$12
$14
$16
$20
$ 60
2.0
2.4
2.8
3.0
3.9
5.0
$ 80
1.8
1.9
2.2
2.7
3.0
4.0
$100
1.2
1.5
1.8
2.1
2.4
3.0
$120
0.9
1.2
1.5
1.8
2.1
2.4
$140
0.9
1.0
1.2
1.5
1.8
2.0
$160
0.8
0.9
1.0
1.2
1.5
1.8

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Copyright 2006 by the University of Nebraska Board of Regents. All rights reserved.
Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.
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