By Blake Jackson
Potato leafhopper numbers are climbing across Pennsylvania, and several alfalfa fields have already crossed the economic threshold.
Recent sweeps in Centre County, along with reports from both the southeast and the west of the state, confirm that populations are high enough in some areas to warrant immediate attention. Because symptoms do not appear until well after feeding starts, growers need to scout now waiting until the “hopper burn” shows up means yield, protein content, and stand life have already been compromised.
These tiny, wedge‑shaped insects do not overwinter in Pennsylvania. Each spring, prevailing storm fronts carry them northward, and they usually reach the state in early June. Once established in an alfalfa stand, adults lay eggs inside stems and leaf veins.
Warm weather speeds development, producing a new generation roughly every three weeks and allowing numbers to explode almost overnight. With their piercing-sucking mouthparts, both adults and nymphs siphon plant sap.
After seven to ten days, the first yellow, triangular lesions appear at leaflet tips; if feeding continues, the yellowing spreads toward the base, signaling that economic losses have already occurred.
Several non‑chemical tactics can lower the risk. Alfalfa varieties bred for leafhopper resistance sport glandular trichomes tiny sticky hairs that discourage feeding and oviposition, but the decision to plant these must be made before a field is seeded.
Mixed stands, such as alfalfa orchardgrass, also tolerate injury better than pure alfalfa. Equally important are natural enemies spiders and predatory insects that thrive when insecticides are used sparingly.
Some Pennsylvania growers who rely on regular scouting and threshold‑based spraying report little or no visible damage, a testament to effective biological control.
If sampling shows that leafhopper counts exceed thresholds, producers have two main options. Taking an early cutting halts feeding and removes many insects with the harvested forage, though the subsequent regrowth must be monitored closely.
When harvest is impractical, select an insecticide labeled for alfalfa and apply it promptly, but only after economic thresholds are met.
Consistent weekly scouting using a sweep net and the recommended stem or sweep counts per inch of plant height remains the key to limiting insecticide applications to, at most, a single treatment each summer while protecting yield and forage quality.
Photo Credit: istock-martijnvandernat
Categories: Pennsylvania, Crops