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Potato Leafhoppers in Alfalfa

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

Potato leafhoppers are a migratory pest that commonly impact alfalfa fields throughout South Dakota. They cannot tolerate our cold winter temperatures, so they travel up from the southern United States each spring. Their annual migration prevents them from becoming an issue until the later alfalfa cuttings.

Feeding injury caused by potato leafhoppers resembles 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).

    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.

    The nymphs (immatures) vary in size and resemble adults except they have wing pads present instead of fully developed wings (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.

    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.

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

      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 and turns them yellow (Figure 3).

      Aside from checking fields for feeding injury, potato leafhopper populations should be scouted for 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), 18 to 24 inches (Table 3), and 24 to 30 inches (Table 4).

      Economic Thresholds

        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.

         
        Insecticide application cost per acre
         
        $8
        $12
        $16
        $20
        Value of hay per ton
        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.

         
        Insecticide application cost per acre
         
        $8
        $12
        $16
        $20
        Value of hay per ton
        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.

         
        Insecticide application cost per acre
         
        $8
        $12
        $16
        $20
        Value of hay per ton
        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

        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 latest South Dakota Pest Management Guide: Alfalfa & Oilseeds.