As we move into late spring/summer, insect activity can begin to increase and, with correct weather conditions, can mean a critical time to begin monitoring crops for potential insect issues. One insect to keep in mind when it comes to alfalfa management is the potato leafhopper (PLH). The PLH is an insect that can impact alfalfa mid-to-late season. This insect does not overwinter in the northern and eastern U.S. but must migrate from southern/southeastern locations every spring, usually by wind associated with storms. As their pattern of movement depends on environmental conditions, predicting or forecasting their potential damage in a given area in a given year can be difficult.
Identification and Damage:
PLH adults are wedge-shaped winged insects that can be varying shades of yellow, to lime green in color and are around 1/8-inch long (Figure 1). After an adult female deposits eggs into the stems and petioles of alfalfa, the eggs hatch in seven to 10 days. The nymphs that emerge are wingless and will become winged adults in about two weeks.
PLH are piercing/sucking insects. and as they feed, they inject a toxin into the plant that can a damage the phloem of the plant, disrupting the normal flow of water and nutrients to the leaves. This combined with the toxin typically manifests into a V-shaped yellowing at leaf tips that can often turn reddish or bronze (Figure 2). These symptoms can also appear as plant necrosis, wilting or mimic fertilizer deficiencies. The toxin can also reduce a stand regrowth potential and can limit nutritional value of an alfalfa crop in severe infestations. The greatest impact that PLH can have, though, is at harvest by limiting alfalfa tonnage and productivity.
As productivity and yield loss can be realized before visible symptoms appear, the best way to determine if management of PLH is necessary is to scout. The best method is using a sweep net to collect and count adult and nymph in a given field. Determining if a chemical treatment is warranted is dependent on the age and height of the stand, as younger or newly established alfalfa fields are more susceptible to damage. The taller the crop is at a given time, the more it will be able to withstand pressures from PLH feeding. Variety differences can also impact PLH management strategies, as certain varieties will be more adapted to withstanding feeding pressures better than others. If thresholds are met, a chemical insecticide may be needed to control the PLH population. The existing stand may also need to be cut to encourage regrowth.
Control recommendations based on alfalfa plant height and number of potato leafhoppers or nymphs per 100 sweeps:2
- Under 3 inches = 20 adult hoppers
- 3 to 8 inches = 50 adult hoppers
- 8 to 12 inches = 100 adult hoppers or nymphs
- Over 12 inches = 200 adults or nymphs
Understand life cycles, identifying impacts and understanding when treatment application may be necessary to control population are all important factors into successfully controlling PLH. By continuing to monitor alfalfa stand health and stage of growth, as well as keeping an eye out for potential new populations of PLH emerging, a producer can help ensure the maximum productivity possible for his or her alfalfa crop can be reached.
1Undersander, D., Cosgrove, D., Cullen, E., Grau, C., Rice, M.E., Renz, M., Sheaffer, C., Shewmaker, G., and Sulc, M. Alfalfa management guide. American Society of Agronomy, Inc.
2Kaatz, P. 2012. Scouting for potato leafhoppers in alfalfa. Know your options for insect control prior to a problem. Michigan State University Extension. https://www.canr.msu.edu/.
Web sites verified 4/13/2020
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