Forages & Grains
Volume 63 Number 18 Date 11/15/2018
ALFALFA WEEVIL - Spring weevil populations in first-crop alfalfa were low in 2018. Larval emergence began in southern Wisconsin by May 15 and peak weevil feeding was predicted for June 1-14 across much of the state. Sweep net counts remained low (<1.0 per sweep) through early June, and leaf tip feeding estimates fell well below the 40% economic threshold in all surveyed fields. Alfalfa fields harvested by mid-June did not sustain significant defoliation. The larval damage period closed before the end of the month.
POTATO LEAFHOPPER - Migrants first arrived in the state during the week of May 24-30, about a week later than normal. DATCP surveys documented low to moderate counts from June through August and chemical control was generally not necessary. Although a few western Wisconsin fields sampled in late July contained localized "hot spots" of high leafhopper counts, none had a fieldwide average exceeding the 2.0 leafhopper-per-plant threshold for alfalfa growth 12 inches or taller. Most sites sampled this year had averages in the range of 0.5-1.5 per sweep.
PEA APHID - Egg hatch was confirmed on May 7. Aphid densities in alfalfa began escalating by mid-May and continued to increase throughout June, which was contrary to their usual pattern of peaking by early June and then decreasing before the end of the month. Counts averaged 18 aphids per sweep during the last week of June, with a few sites containing very high numbers of 25-35 per sweep. Populations declined markedly by the third week of July and remained low in August. The season's highest count of 35 aphids per sweep was recorded on July 3 in Green Lake County.
-- Krista Hamilton, DATCP Entomologist