How to Protect Alfalfa from Potato Leafhopper Damage This Summer

By Blake Jackson

Alfalfa growers should begin preparing for the arrival of potato leafhoppers, a common and damaging pest that typically appears in Pennsylvania during early summer.

According to John Tooker, Professor of Entomology at Penn State Extension, these insects usually migrate into the region on storm fronts in June. Although they may not yet be present, conditions such as incoming rainfall could trigger their arrival, making early scouting essential.

Potato leafhoppers are considered one of the most harmful pests affecting alfalfa, though they can also damage other legume forages and certain vegetable crops. Their feeding reduces overall yield, lowers forage quality—especially protein content—and can shorten the lifespan of stands.

These pests tend to appear unpredictably, which makes management challenging. 

Once in a field, adult leafhoppers lay eggs inside plant stems and leaf veins. Under warm conditions, these eggs develop quickly, allowing populations to grow rapidly in a short period.

Leafhoppers feed by piercing plant tissue and extracting sap. This disrupts the plant’s ability to transport nutrients, leading to a condition known as “hopper burn.” This damage appears as yellowing, triangular lesions at the tips of leaves but typically develops 7 to 10 days after feeding begins. By the time symptoms are visible, economic losses have often already occurred.

If infestations reach damaging levels, early harvest or insecticide application may be necessary. Early cutting can help stop further loss, but regrowth should be monitored carefully, as pests can return quickly.

Long-term management strategies include planting leafhopper-resistant alfalfa varieties, which have fine leaf hairs that deter feeding. Mixing alfalfa with grasses such as orchardgrass can also improve tolerance to damage.

Additionally, integrated pest management (IPM) practices can be effective. Natural predators like spiders help control leafhopper populations, reducing the need for chemical treatments when pest levels remain below economic thresholds.

Recommendations for Alfalfa Growers:

• Monitor alfalfa fields in early June to detect leafhopper presence before damage occurs.
• Apply insecticides only when populations exceed economic thresholds to reduce unnecessary costs.
• Cut alfalfa early if infestations reach high levels to limit further feeding damage.
• Use leafhopper-resistant alfalfa with glandular hairs to reduce pest pressure.
• Combine alfalfa with grasses like orchardgrass to improve crop resilience.

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