The Gulf tropical depression Christobal has been making headlines with heavy rains experienced in the South and expected in parts of the Midwest. But there is more than just rain that arrives with these storm systems; they also carry migratory pests that can’t overwinter in Kentucky. One of those pests to expect is potato leafhopper, a migratory insect that moves north on warm south winds from the Gulf States each spring.
While potato leafhopper (Figure 1) is pest of alfalfa in general, it is more problematic in spring-seeded alfalfa. Potato leafhopper is tiny and easily overlooked, but size has little to do with importance as a pest. Spring-seeded alfalfa needs to be monitored regularly for this pest until the first cutting. The extended 70 to 90 day growth period before first harvest allows time for damaging numbers of leafhopper numbers to build and damage stands. More frequent cuttings of established alfalfa helps to manage potato leafhopper numbers. Significant numbers of leafhoppers often find their way into spring-seeded fields in spring, with a rapid increase during June and a peak in early July; they usually disappear from Kentucky alfalfa fields in late July.
Potato leafhopper (PLH) can impact alfalfa in several ways. Insertion of their piecing-sucking mouthparts to feed on sap physically damages vascular tissues of stems and leaves, and it blocks the phloem. The characteristic symptom is called hopperburn and results from the accumulation of photosynthates in leaves near the blockage. It begins as a V-shaped wedge of yellow extending from about the middle of the leaf to the tip (Figure 2). This damage can result in stunted growth, premature leaf-drop, reduced root carbohydrate reserves, and drastic reductions in protein content of hay. PLH can reduce yields up to 25%, as well as lower crude protein, vitamin A, carotene, calcium, phosphorus, and digestible dry matter content.
Monitoring for Potato Leafhopper
Regular monitoring of spring-seeded fields alerts us to potentially damaging potato leafhopper populations before they damage fields. Fields are sampled with a 15-inch diameter sweep net. Five sets of 20 sweeps are taken from randomly selected areas representing the entire field. These leafhopper numbers, coupled with the average plant stem height, is used to determine if a leafhopper treatment is needed. For more information, read ENTFACT-115 ‘Potato Leafhoppers’.
By Ric Bessin, Entomology Extension Specialist