Forages & Grains
Volume 63 Number 5 Date 05/31/2018
ALFALFA WEEVIL - Larval populations remain low for late May. Surveys found no more than 21 larvae per 100 sweeps, with an average of only five per 100 sweeps. Defoliation is currently below 10% in most fields but will become more conspicuous next week as larvae transition into the larger and most destructive third and fourth-instars. First-crop alfalfa should be cut soon to avoid unnecessary insecticide treatment.
POTATO LEAFHOPPER - The first distinct migration into Wisconsin has occurred and leafhoppers are appearing in low numbers in alfalfa. Adults were collected in 25% of fields surveyed from May 24-30, from Grant to Outagamie County. This insect customarily arrives in Wisconsin around the time the first alfalfa crop is harvested and under favorable hot conditions can rapidly increase to damaging levels in the second crop.
PLANT BUG - Populations escalated sharply in the past week with the addition of many small nymphs. Both the tarnished and alfalfa plant bug species are common in sweep net collections.
PEA APHID - Densities currently range from 1-4 per sweep in surveyed fields. Counts of this level are considered non-economic in alfalfa, though aphid populations can escalate rapidly when natural enemy populations are disrupted by alfalfa weevil insecticide sprays. Harvesting fields on time rather than using insecticidal control is important for preserving natural enemies.
-- Krista Hamilton, DATCP Entomologist