Potato Leafhopper – A Key Pest Of Spring-Seeded Alfalfa

 Figure 1. Wedge-shaped foliar symptom of potato leafhopper attack.
 Photo: Lee Townsend, UK


   Potato leafhopper (PLH) is a key pest of spring-seeded alfalfa, as well as the second, and occasionally third, cuttings from established fields. Small size makes PLH an easily overlooked but costly pest. Top pest management priority should go to spring-seeded stands. The recommended 70 to 90 day growth period before first harvest allows time for damaging numbers of PLH to develop. Watch spring-seeded stands closely and treat if necessary.
   The first 10 to 14 days after the first cutting is removed from established fields is very important. This is when PLH adults fly in to feed and lay eggs in tender regrowth. Females insert their eggs in stems and large veins of alfalfa plants. A 21-day live cycle means the population can increase rapidly. The small wingless immature stages (nymphs) have limited movement so their feeding damage can be concentrated and intense.
   PLH is a migratory insect that moves north from the Gulf States each spring on warm south winds. It shows up in established alfalfa fields during May, but the date can vary from the first to the last of the month in any given year. Significant numbers of leafhoppers may find their way into spring-seeded fields in spring with a rapid increase during June and a peak in early July. The leafhopper usually disappears from Kentucky alfalfa fields in late July. More information on this insect is available in the Extension publication, Potato Leafhoppers (ENTFACT-115).
   In a recent study, researchers demonstrated the impact of climate change on this specific migratory pest. PLH arrives in northern states an average of 10 days earlier than it did in the 1950s and it is causing more damage in years with warmer average temperatures. With a host range of more than 200 plants from alfalfa to hops, the importance of this insect is increasing across the country.
   Potato Leafhopper Damage
   PLH can affect alfalfa in several ways. Insertion of their piercing sucking mouthparts to feed on sap physically damages vascular tissues of stems and leaves, and it blocks the phloem. Hopperburn, the characteristic symptom, results from the accumulation of photosynthates in leaves. It begins as a V-shaped wedge of yellow extending from about the middle of the leaf to the tip (Figure 1).
   PLH impact on plants is significant and can include stunted growth, premature leaf-drop, reduced root carbohydrate reserves, and drastic reductions in protein content of hay. In sufficient numbers, PLH can reduce yields up to 25 percent, as well as lower crude protein, vitamin A, carotene, calcium, phosphorus, and digestible dry matter content.
   Scouting Potato Leafhopper
   Reducing losses means detecting potentially damaging numbers of PLH before symptoms appear. Adults are small and flighty; nymphs are even smaller. Detection and assessment of populations require a 15-inch diameter sweep net. Alfalfa fields must be checked carefully with a sweep net to detect damaging numbers before symptoms appear. Five sets of 20 sweeps from randomly selected areas in a field, coupled with the average plant stem height, is the way to detect and assess the pest before the crop is hurt.
Managing Potato Leafhopper
   A single, well-timed application of any one of several insecticides will provide excellent leafhopper control if numbers exceed treatment guidelines. Refer to the Extension publication, Potato Leafhoppers (ENTFACT-115) for more information.
   Cultural Practices
   A 35-day harvest schedule generally keeps leafhoppers from building to large numbers. Cutting drives the winged adults out of the field. The wingless nymphs are unable to leave and most starve or die from some other cause before regrowth starts. ∆
   DR. LEE TOWNSEND: Extension Entomologist, University of Kentucky

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