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Issue No. 10, Article 1/June 10, 2011

Reports of Potato Leafhopper Activity and Spraying Received

Potato leafhoppers are active, and alfalfa should be scouted for these insects, which can inflict economic losses to stands. I received a report on June 7 that potato leafhoppers have reached densities of 1.0 per sweep in some stands (alfalfa 4 to 7 inches high) located near Greenville, in Bond County in southwestern Illinois. When alfalfa is 6 to 12 inches high, a density of 1.0 leafhopper per sweep has the potential to cause economic losses.

Factors in deciding whether to treat an infestation are the value of the hay, the height of the alfalfa, and the cost of the insecticide application. Let's take an example: For alfalfa 4 to 8 inches high, the economic threshold for potato leafhoppers would be 0.5 per sweep, hay would be valued at $120 per ton, and an insecticide application would cost $12 per acre. If the value of hay is reduced to $60 per ton while the insecticide cost remains the same, the economic threshold increases to 1.0 per sweep (see Table 1 for this and other treatment thresholds). The use of a standard 15-inch sweep net is key to effectively scouting and managing potato leafhoppers in alfalfa.

Table 1. Treatment thresholds for potato leafhoppers (average number per sweep) on alfalfa at various heights.

Value of hay per ton

Cost of insecticide application per acre

$8

$10

$12

$14

$16

$20

Alfalfa 1 to 4 in. tall

$60

0.4

0.5

0.6

0.7

0.8

1.0

$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

$160

0.15

0.2

0.3

0.3

0.3

0.4

Alfalfa 4 to 8 in. tall

$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

Alfalfa 8 to 12 in. tall

$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

Adult potato leafhoppers are 1/8-inch long, pale green, wedge-shaped, and equipped with needle-like mouthparts with which they suck fluids from plants and inject their saliva. As a result of their feeding activity, the distribution of nutrients within the plant is disrupted. V-shaped yellowish areas may begin to appear on the tips of leaves, a phenomenon often referred to as "hopper burn." This discoloration may be misdiagnosed as a disease or a nutrient deficiency, most notably of boron. A deficiency of boron in plants is most often confined to younger leaves.


Adult potato leafhopper. (Photo courtesy Matt Montgomery, University of Illinois Extension.)

Large densities of potato leafhoppers can reduce protein and vitamin A in alfalfa and lower its nutritional value for livestock. Three to four generations of potato leafhoppers per year typically occur in Illinois. Above-average temperatures throughout the season accompanied by dry conditions may lead to increased feeding and damage. Visit the following like for more information about the biology, life cycle, and management of potato leafhopper.--Mike Gray

Author:
Mike Gray

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