Potato Leafhoppers in Alfalfa Back »

Written collaboratively by Patrick Wagner, Amanda Bachmann, Philip Rozeboom, and Adam Varenhorst.

In alfalfa, one of the mid to late season insect pests to watch for is the potato leafhopper. Potato leafhoppers are a migratory pest that commonly impact alfalfa fields throughout South Dakota. They do not overwinter here because they cannot tolerate the cold winter temperatures. Instead, they travel from the southern United States each spring and become an issue for the later alfalfa cuttings. Feeding injury caused by potato leafhoppers resemble drought stress and, if left untreated, can reduce both yield and forage quality.

Profile

Adult potato leafhoppers are approximately 1/8 of an inch long and pale green in color. They have translucent wings that cover their bodies like a tent when at rest (Figure 1). The potato leafhopper nymphs (immatures) vary in size and resemble the adults except they do not have fully formed wings. Nymphs that are in the later developmental stages will have wing pads visible on their backs (Figure 2). Both the nymphs and adults have specialized hind legs that allow them to jump long distances. They also have piercing-sucking mouthparts that they use to feed on plant sap. Potato leafhoppers should not be confused with aster leafhoppers, which can be identified by dark markings on their heads.

Small pale green leafhopper on a green alfalfa leaf.
Figure 1. Adult potato leafhopper. Courtesy: Patrick Wagner

Small green leafhopper nymph on a green leaf.
Figure 2. Potato leafhopper nymph. Notice that the wings have not yet fully developed. Courtesy: Frank Peairs, Colorado State University, Bugwood.org

Scouting

It is important to routinely scout alfalfa fields for potato leafhoppers to ensure that serious injury does not occur. Large populations of potato leafhoppers will cause stunted plants and may lead to significant losses to the tonnage and quality of the alfalfa crop. One of the first signs of a potato leafhopper infestation is the appearance of “hopper burn” in the field. Hopper burn occurs when potato leafhoppers use their mouthparts to probe the plants, which disrupts the cells within the leaves turning them yellow (Figure 3). As mentioned previously, this characteristic injury is often mistaken for drought stress. First year alfalfa is at a greater risk for severe potato leafhopper injury, but all alfalfa fields should be scouted.

Green alfalfa leaves turning yellow because of potato leafhopper feeding.
Figure 3. Hopper burn symptoms on alfalfa. Courtesy: Adam Varenhorst

Aside from checking fields for feeding injury, potato leafhopper populations should be scouted using a sweep net. It is best to sample the field edges because this is where potato leafhoppers tend to be more of an issue. While walking in a “W” or “Z” pattern, swing the net in a 180-degree pendulum swing 25 times. Each of the pendulums (left to right) counts as a single sweep. Count the total number of nymph and adult potato leafhoppers present in the net. Next, measure the height of the alfalfa plants. Economic thresholds for alfalfa are based on plant height; 0 to 12 inches tall (Table 1), 12 to 18 inches (Table 2), and 18 to 24 inches (Table 3).

Management

If management of potato leafhoppers is necessary, there are a few recommendations to consider:

  1. Plant resistant alfalfa varieties (alfalfa that has glandular hairs or trichomes). The hairs present on the stems and leaves of these varieties prevent the adults from successfully feeding, and the nymphs may become caught and will eventually starve.
  2. Cut alfalfa when a potato leafhopper infestation is detected. This method is capable of disrupting potato leafhoppers and forcing them to migrate out of the field. However, there is a chance that populations will re-infest the alfalfa regrowth.
  3. Use insecticides to reduce potato leafhopper populations and minimize the chances of injury to the developing alfalfa. The economic thresholds for potato leafhoppers are dependent on the value of hay, cost of insecticide application, and the size of the plant. For a list of insecticides that are currently labeled for potato leafhopper management, refer to the 2018 South Dakota Pest Management Guide: Alfalfa & Oilseeds.

Table 1. Alfalfa 0 to 4 inches tall. Economic thresholds for potato leafhoppers based on number of leafhoppers (nymphs and adults) calculated from the total of a 25-sweep sample.

Value of hay per ton
Insecticide application cost per acre
$8 $12 $16 $20
Total potato leafhoppers per 25 sweeps
$60 13 20 27 33
$80 10 15 20 25
$100 8 12 16 20
$120 7 10 13 17
$140 6 9 11 14
$160 5 8 10 13
$180 4 7 9 11
$200 4 6 8 10
$220 4 5 7 9


Table 2. Alfalfa 4 to 8 inches tall. Economic thresholds for potato leafhoppers based on number of leafhoppers (nymphs and adults) calculated from the total of a 25-sweep sample.

Value of hay per ton
Insecticide application cost per acre
$8 $12 $16 $20
Total potato leafhoppers per 25 sweeps
$60 19 29 38 48
$80 14 21 29 36
$100 11 17 23 29
$120 10 14 19 24
$140 8 12 16 20
$160 7 11 14 18
$180 6 10 13 16
$200 6 9 11 14
$220 5 8 10 13

 

Table 3. Alfalfa 8 to 12 inches tall. Economic thresholds for potato leafhoppers based on number of leafhoppers (nymphs and adults) calculated from the total of a 25-sweep sample.

Value of hay per ton
Insecticide application cost per acre
$8 $12 $16 $20
Total leafhoppers per 25 sweeps
$60 67 100 133 167
$80 50 75 100 125
$100 40 60 80 100
$120 33 50 67 83
$140 29 43 57 71
$160 25 38 50 63
$180 22 33 44 56
$200 20 30 40 50
$220 18 27 36 45
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