Potato Leafhopper (PLH) is an economically important pest of alfalfa in the Midwest and eastern portions of the U.S. Infection by PLH causes reductions in yield, quality, and stand longevity. Several generations can be present in a field at any given time. Early scouting and variety selection is imperative for appropriate control and decrease impacts on alfalfa stands. Potato leafhopper infestations are particularly damaging to new seedings, and so close monitoring is important to limit impacts on these stands, as failure to do so can limit yield throughout the lifetime of the stand
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Identification and lifecycle:
- Eggs are deposited in stems and leaf veins, hatching into nymphs in 7-10 days
- Nymphs are bright green in color, looking similar to adults, but are wingless
- Nymphs progress to adults in 2-3 weeks, depending on environment
- Adults are winged, pale-green, and wedge-shaped
When should we look for them?
- Depending on location, infestation generally occurs between April- August
- Most damage often occurs after first harvest
- Farther south experience earliest population infestations
- Potato leafhoppers overwinter in the Gulf states, migrating north each spring
- Females begin depositing eggs immediately
- Carried along by air currents and storm systems
- Population increases are favored by dry, warm weather conditions- 86°F optimal temperature
- Scout new seedings early in the spring, as they experience the biggest impacts
What does their damage look like?
- Damage generally most noticeable after economic thresholds are met
- Nymphs and adults feed on plants by injecting toxic saliva into plants
- Allows them to “suck” plant sap
- A light-green, V-shaped wedge at the edge of the leaflet is characteristic of PLH feeding
- Can also take on a rust or red color
- Commonly referred to as “hopper burn”
Figure 1. Picture of a Potato leafhopper adult (top) and nymph (bottom). Photo credit: Penn state College of Agricultural Sciences.
Figure 2. Map depicting population movement and distribution throughout the U.S. Photo credit: University of New Hampshire Extension.
What is the economic threshold for control?
- Sweep net collection is the easiest method of population estimation
- Take at least 100 sweeps throughout a field
- Most straightforward economic threshold numbers are:
- 0.2 PLH/ sweep for ≤ 3” tall alfalfa
- 0.5 PLH/ sweep for 3-8” tall alfalfa
- 1 PLH/ sweep for 8-12” tall alfalfa
- 2 PLH/ sweep for ≥ 12” tall alfalfa
Figure 4. Comparison of resistant variety (plot on left) compared to a susceptible variety (plot on right) under PLH pressure. These plots were located at the Forage Genetics International’s research station in Mt. Joy, PA.
What can we do to control?
- Utilize resistant varieties whenever possible
- Won’t reduce population density or kill PLH, but will reduce impact to stand
- Harvest if approaching economic threshold population levels
- Forces PLH out of field in search of new food
- Monitor regrowth, as they can move back into field quickly
- Utilize insecticides when populations reach economic thresholds
- Always scout prior to ensure that populations are at levels warranting control
- Chemicals are most useful on susceptible varieties, however, may still be necessary in resistant alfalfa varieties
- Follow all label directions, and avoid spraying in the middle of the day when beneficial populations may be more negatively impacted
Source: 2021 Forage Genetics International, LLC -