Potato Leafhopper in Alfalfa
Alfalfa growers can suffer yield losses from potato leafhopper (PLH) damage. Here are tips to scout and manage PLH pressure.
- Wounds from PLH feeding cause leaf chlorosis ("hopperburn") and plant stunting.
- Initial symptom is V-shaped yellowing at leaf tips.
- With severe or prolonged PLH feeding stress:
- Leaves turn reddish or bronze.
- Plants stop growing and appear stunted.
- 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
- 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.
- Growers have a choice of several effective insecticides.
- 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.
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.
- Resistance comes from small hairs on the stem that repel the leafhopper.
- Pioneer® 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.
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.