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Potato Leafhopper in Alfalfa

 

Potato Leafhopper in Alfalfa

Alfalfa growers can suffer yield losses from potato leafhopper (PLH) damage. Here are tips to scout and manage PLH pressure.

Symptoms

  • Wounds from PLH feeding cause leaf chlorosis ("hopperburn") and plant stunting.
  • Initial symptom is V-shaped yellowing at leaf tips.
Alfalfa plant leaves showing wounds from potato leafhopper feeding.
  • With severe or prolonged PLH feeding stress:
    • Leaves turn reddish or bronze.
    • Plants stop growing and appear stunted.
With severe or prolonged potato leafhopper feeding stress, alfalfa leaves turn reddish or bronze.
  • The shorter the alfalfa, the more susceptible it is to damage from PLH. This includes:
    • Very young plants
    • Early stages of regrowth
    • Stress by other factors

Potato Leafhopper Identification

Adult potato leafhoppers are yellowish, lime-green, wedge-shaped insects about 1/8 inch long.
  • Adults are yellowish, lime-green, wedge-shaped insects about 1/8 inch long.
  • Nymphs are paler in color, smaller in size and lack wings.
  • Adults jump or fly when disturbed.
  • Nymphs crawl rapidly sideways and hide when disturbed.

Potato Leafhopper Facts

  • One of the most common and destructive insects affecting alfalfa.
  • No reliable method to forecast damage.
  • Scouting fields and using a sweep net is the only effective method to monitor PLH activity.
  • Once visible symptoms of hopperburn and plant stunting become evident, it is too late for corrective action.
  • PLH-resistant alfalfa varieties can simplify and improve management.

Life Cycle and Development

  • Adults overwinter in the southern/southeastern US.
  • Adults migrate to the northern and eastern US in the spring, carried by prevailing weather systems.
  • Females deposit eggs into the stems, petioles and leaf veins of alfalfa.
  • Eggs hatch in 7-10 days into wingless nymphs that become fully grown winged adults in about 2 weeks.
  • Populations greatly increase by early summer.
  • Can cause major economic damage on new seedlings and second- and third-cutting alfalfa.
  • Optimum temperatures for reproduction and growth are between 70 and 90 degrees F.

Impact on Crop

  • Greatest impact on crop is yield reduction.
  • Severe damage can reduce crude protein content, carbohydrate reserves in taproot and plant regrowth.

Management Practices

Chemical Control

  • Growers have a choice of several effective insecticides.
Alfalfa growers have a choice of several effective insecticides to control potato leafhopplers.

Mechanical Control

  • Harvesting infected stands may be required.
  • Harvesting potentially reduces egg, nymph and adult populations.
  • Harvesting severely damaged alfalfa stands may be the only method to initiate regrowth of alfalfa stems.
Harvesting alfalfa stands infected with leafhoppers potentially reduces egg, nymph and adult populations.

Thresholds for Treatment

  • Scout alfalfa field using a sweep net.
  • For non-PLH resistant varieties, spray when leafhopper count per 10 sweeps exceeds average plant height in inches.
  • For PLH-resistant varieties, spray when leafhopper count per 10 sweeps exceeds 3X the alfalfa height in inches.

PLH-Resistant Varieties

  • Resistance comes from small hairs on the stem that repel the leafhopper.
  • PioneerĀ® brand 55H94 has best-in-class leafhopper resistance when compared to competitor varieties.
  • Pioneer 55H94 has outperformed competitors in Pioneer and university trials across multiple locations and years.
  • This variety is recommended where intense PLH pressure spans 2 to 3 cuts per year.
  • Because not all plants in an alfalfa variety are genetically identical, some plants in a PLH-resistant variety do not carry PLH resistance.
    • Some feeding symptoms may be noticed on non-PLH plants.
Alfalfa potato leafhopper-resistant variety on left, non-resistant variety on the right.

PLH-resistant variety on left, non-resistant variety on right (differences may not be this extreme in all cases).

Selecting a Resistant vs. Non-resistant Variety

  • If scouting and spraying offer adequate control, growers may choose varieties that are not PLH resistant.
  • If scouting and spraying does not normally control potato leafhopper, a PLH-resistant variety is a good choice.
  • First-year PLH-resistant alfalfa may need chemical control.
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