Bryan Jensen, Dept. of Entomology and Integrated Pest Management Program, University of Wisconsin-Madison
Although the Arlington Agricultural Research Station is a small sample size, it appears we have received a migration potato leafhopper lately. No surprise based on the preceding warm weather. I am sure DATCP’s Pest Bulletin will have more to add on potato leafhopper populations when their newsletter comes out.
It does serve as a warning to start scouting alfalfa. Typically, when the migration does arrive we will go through a period of population buildup IF weather is favorable (hot/dry). At this point I am not overly concerned about second crop, however scouting will tell you for sure. Third cut would typically be when we should be sweeping on a regular basis. By this point in time we would have completed at least one generation and potentially see a significant increase in damage potential. New seedings are a different story. They should be spot-checked now. New seedings are as attractive to adults as established stands are and there is a longer time between harvest which allows numbers to increase.
In established stands avoid automatic stubble spraying after harvest even if populations are high. Leafhopper adults will leave the harvested field because its food source has been removed. Nymphs will usually die because of the lack of food. This forces adults to recolonize fields and you never know if or when that might happen. The best system would be to scout the field as soon as regrowth is 3 inches tall and make spray decisions based on current potato leafhopper populations. This avoids either unnecessary applications or allows application that is better timed. After first cut in new seedings there is usually some green stem or leaf materials that can sustain nymphs and keep adults in the field. Scout these field immediately after harvest to determine damage potential.