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Degree Days

Corn
Volume 64 Number 9 Date 06/27/2019


TRUE ARMYWORM - Larvae have been active in corn and winter rye cover crop fields in the local area east of Fond du Lac, where some V5 corn has reportedly been treated for armyworm control. DATCP surveys found non-economic damage affecting 1-2% of corn plants in about 30% of sites checked in the past week. Field conditions remain very favorable for armyworm problems, and this week's observations suggest that increased vigilance is in order.

EUROPEAN CORN BORER - The spring flight of moths has peaked in southern and central Wisconsin. Black light trap counts have been low since the flight began during the week of May 30-June 5, with weekly counts ranging no higher than 14 moths per trap. Oviposition is intensifying and shot hole feeding by first-instar ECB larvae was confirmed on June 26 in Dane County.

WESTERN BEAN CUTWORM - Pheromone traps are now being placed at selected sites statewide in preparation for the annual moth flight. Participants in the western bean cutworm monitoring program should begin reporting counts to Tracy Schilder at tracy.schilder@wisconsin.gov no later than July 3.

CORN ROOTWORM - Egg hatch has been underway since early June and will peak across much of the state by early to mid-July. Corn root pruning assessments can begin about a week after the peak (50% egg hatch) has occurred. Continuous corn and areas with Bt performance issues should be the highest priority for inspection and root ratings.

GRANULATE CUTWORM - This moth, which closely resembles the western bean cutworm (WBCW) adult, often appears in black light traps 1-2 weeks in advance of the WBCW flight. The granulate cutworm is noticeably smaller, about of the size of the WBCW moth. Based on below-normal degree day accumulations, the annual flight of WBCW adults is unlikely to begin until the first week of July this year.

STALK BORER - Larval infestations are below 5% in most fields. This perimeter pest migrates from perennial grasses and broadleaf weed hosts in June and infests mainly the first 4-6 rows of corn. Significant damage is unlikely once plants have developed past the V7-V8 stages. Spot treatment should be considered if 4-5% of plants are infested.

BLACK CUTWORM - The threat from this usually early-season pest has not subsided. On June 24, a crop consultant reported that he observed "the largest infestation of black cutworm in at least 15 years" in Fond du Lac County corn. The field was previously alfalfa no tilled into corn. Although DATCP surveys have found scattered, minor black cutworm infestations this month, severe cutworm problems appear to be isolated, which is surprising given the late planting season and large spring moth migration. Continued scouting is recommended for corn that has not yet reached the V5 stage.

-- Krista Hamilton, DATCP Entomologist