Forages & Grains
Volume 64 Number 9 Date 06/27/2019
POTATO LEAFHOPPER - Nymphs are appearing in second-crop alfalfa. Counts in 10 to 16-inch fields in Buffalo, Eau Claire, Trempealeau, Pepin and Pierce counties are below threshold at 0.3-0.8 per sweep, while levels in Dodge, Green and Rock counties are similar at 0.2-0.6 per sweep. The weekly average in 32 surveyed fields was 0.5 per sweep. Crop scouts are reminded that potato leafhopper nymphs are seldom recovered in the bottom of the sweep net with the adults, but are instead found around the collar of the net. The neon-green nymphs move sideways when disturbed. Economic thresholds for this pest are based on mixed counts of adults and nymphs and are as follows: 0.5 per sweep for 3- to 7-inch alfalfa, 1.0 per sweep for 8- to 11-inch alfalfa, and 2.0 per sweep for alfalfa 12 inches or taller.
ALFALFA WEEVIL - Larval populations are now less than 0.2 per sweep and pupation is beginning in southern and central Wisconsin. The alfalfa weevil season is expected to end by early July without significant damage observed this year. Nevertheless, alfalfa should be regularly scouted through harvest and until new growth of the second crop is established.
PLANT BUG - Surveys conducted in the southern west-central counties yielded unusually low averages of less than 0.2 adults and nymphs per sweep, which is very low in comparison to the economic threshold of five per sweep in alfalfa. Both the alfalfa plant bug and tarnished plant bug species can be found in sweep net collections.
PEA APHID - Average counts of this insect remain similar to last week at four per sweep, with a range of 1-10 per sweep. Pea aphid levels have increased throughout June, which is contrary to their usual pattern of peaking by early June and then decreasing sharply before the end of the month.
-- Krista Hamilton, DATCP Entomologist