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Forages & Grains
Volume 65 Number 4 Date 05/21/2020 ALFALFA WEEVIL - Larvae had not been found in any alfalfa field sampled as of May 20. The alfalfa weevil phenology model forecasts the first emergence of larvae for 300 degree days (sine base 48°F), which should be reached by May 22 near Beloit, May 24 in Madison, May 25 at Eau Claire, and June 2 near Wausau. POTATO LEAFHOPPER - A migration appears to have occurred in the past week, with leafhoppers collected from 5 of 44 (11%) alfalfa fields surveyed May 19 and 20. This insect arrives annually in Wisconsin in mid- to late May, as harvest of the first alfalfa crop is approaching. These long-distance migrants are predominantly mated females which arrive ready to lay eggs and initiate a new generation. PEA APHID - Counts are beginning to increase. Alfalfa swept this week contained an average of 66 per 100 sweeps, while last week's average was only six aphids per 100 sweeps. TARNISHED PLANT BUG - Adults are common in alfalfa, though counts remain very low. Surveyed fields in Dane, Grant, Green, Iowa, Jefferson, La Crosse, Lafayette, and Monroe counties had an average of six per 100 sweeps. The economic threshold for plant bugs in alfalfa of five per sweep (or 500 per 100 sweeps) is seldom exceeded until later in summer, but their relative abundance in spring can be an indicator of potential problems for apples, strawberries and other fruit and vegetable hosts. -- Krista Hamilton, DATCP Entomologist 
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