Introduction
The potato leafhopper (PLH), Empoasca fabae, feeds on over 100 cultivated and wild plants including alfalfa, clover, eggplants, strawberries, some garden flower varieties, potatoes, soybeans, and snap beans. In the upper Midwest, PLH will typically achieve high populations in late June to early August. Thus, snap beans will usually be an attractive host.

Biology and Life cycle

PLH adults are lime green, slender, small (1/8" long), and somewhat wedge-shaped with heads that are slightly broader than the rest of their bodies. They usually have 6 small white dots directly behind their head that can be seen with magnification. The nymphs look similar to the adults except that they are smaller, wingless, and paler green (see image, left). Both the adults and nymphs are very active. The adults jump or fly away as you walk through the field or brush your hand over plants. If you disturb the nymphs, they move very quickly in a distinctive sideways movement across the leaf in an effort to hide on the underside of the leaf. Nymphs develop between 54 to 88 F, with development most rapid at 86 F.

PLH do not overwinter in the upper Midwest. They migrate from the southern United States on wind currents and start arriving in the upper Midwest in mid to late May. The females, often fertilized, are usually the first to arrive. Large populations continue to migrate through June and early July. PLH lays eggs in the stems of susceptible plants. Each female lays 2-3 eggs per day and continues to oviposit for at least a month and up to 50 days. Eggs hatch in 7 to10 days. Nymphs molt five times from 1st instar to adult in about two weeks. Nymphs feed primarily on the underside of the leaf. Given their limited mobility, nymphs are considered more damaging than adults. There are usually two generations per year in the upper Midwest. However, because of the long oviposition period, infestations usually consist of overlapping generations.

Damage

PLH have piercing-sucking mouthparts with both adults and nymphs causing damage on beans. When they insert their mouthparts into the water and food conducting tissue of plants, they also inject saliva and create physical damage that plugs the vascular tissue. The first signs of feeding are pale leaf veins and curling leaves (see image, left). Continued feeding results in most or all of the leaf curling, crinkling, and turning brown. Sometimes, the damage is a characteristic v-shaped brown area at the leaf tip that is called hopperburn. In addition, other damage symptoms include stunted growth, shortened internodes, and fewer flowers and pods. Other insects such as aphids, which also have piercing-sucking mouthparts, cause similar deformities. Curled, chlorotic foliage may also be a symptom of a nutrient deficiency. Therefore, proper identification of the source of the damage is important for making management decisions.

Management

Several predators, fungal pathogens, and parasites such as the mymarid egg parasite, Anagrus epos, attack PLH. None of these natural enemies, however, are usually effective in controlling PLH. Chemical insecticides are usually the best way to control PLH. Since the arrival of PLH varies every year, scouting for PLH should start by mid-May.

Monitoring Adults. Monitor adult populations with a sweep net or by placing sticky cards at field edges. Sticky cards are useful in first detecting the arrival of PLH, but after that point using a sweep net or visual sampling is an easier way to determine population levels in a field. Take 10 sweeps per sample site with at least 5 sample sites per 50-acre field. Sample locations should be spread out over a field as much as possible. Avoid sweep net sampling in winds greater than 10 mph.

Monitoring Nymphs. Monitor nymph populations by looking at undersides of leaves. Carefully turn over 10 leaves per sample site and count nymphs as they scurry for cover. Use at least 10 sample sites per field.

Insecticidal Control - Foliar Treatments

If thresholds have been reached, several insecticides can be used to control PLH. To ensure proper rates and use of insecticides please refer to the most recent edition of the Midwest Vegetable Production Guide.

Recent research regarding insecticide-treated seed has shown promising results in controlling PLH. Two recent products, Gaucho (Gustafson) and Cruiser (Syngenta Corp.), known as "neonicotinoids", are unique in that they provide both direct protection from soil-borne insects to the developing root tissue, as well as systemic activity throughout the seedling, from germination to about 3-4 weeks following emergence. Both products provide good to excellent control of PLH. As of May 2003 however, only Gaucho was currently labeled for snap bean (as well as sweet corn and other vegetables). Cruiser is labeled for sweet corn, but the application for snap bean is still pending. It is interesting to note that in Minnesota trials, Cruiser provided a slight, but a statistically higher level of PLH control over Gaucho (Koch, Burkness, Hutchison & Rabaey, unpublished data). In similar studies in New York and Minnesota, Cruiser also provided significantly higher levels of PLH control (B. Nault, Cornell Univ., personal communication, 2/03).

NOTE: To ensure proper rates and use of insecticides please refer to the most recent edition of the Midwest Vegetable Production Guide.

Vigorously growing plants more easily withstand feeding damage. Good cultural practices (e.g., weed control, stand establishment) result in healthy plants that can tolerate higher levels of damage. Crops planted near alfalfa fields tend to suffer more damage, especially after alfalfa is harvested and PLH are forced out of the field.

Little information is available on varietal tolerance to PLH. However, Tendercrop cultivars are less susceptible to damage than Blue Lake cultivars.

Selected References

Burkness, E.C., P.K. O'Rourke, & W.D. Hutchison. 2000. Control of European corn borer and potato leafhopper in Minnesota snap beans, 1999. Arthropod Management Tests. 25.

Cornell University. 2003. Vegetable Disease ID and Management http://vegetablemdonline.ppath.cornell.edu/

Foster, R. & B. Flood. 1995. Vegetable Insect Management. Meister Publishing Co. Willoughby, Ohio.

Gonzalez, A.L. and J.A. Wyman. 1991. Effect of varying potato leafhopper (Homoptera: Cicadellidae) population densities on snap bean yield. J. Econ. Entomol. 84: 644-649.

Metcalf, R.L. & R.A. Metcalf. 1993. Destructive and Useful Insects. 5th Edition. McGraw-Hill, Inc. New York.

Tingey, W.M. & A.A. Muck. 1983. Vegetable Crops: Potato Leafhopper. Eds. C.H. Petzoldt, L.H. Pedersen, C. Koplinka-Loehr, & M. Haining Cowles. Snap Bean Pest Management.5th Edition. Cornell University.

University of Minnesota Extension Service BU-7094-S. Midwest Vegetable Production Guide for Commercial Growers. http://www.btny.purdue.edu/Pubs/ID/ID-56/

Vegetable Crop Scouting Manual. Integrated Pest Management Program-University of Wisconsin Extension, Cooperative Extension Service. Madison, WI, 1998.

K. Van Wychen Bennett, W.D. Hutchison, E.C. Burkness, R.L. Koch, & B. Potter. 2003. Bean Leaf Beetle - Snap Beans. VegEdge Fact Sheet. Univ. of Minn. St. Paul, Minn.