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Corn
Volume 64 Number 4 Date 05/23/2019


BLACK CUTWORM - Significant flights were again registered at several DATCP monitoring sites during the week ending May 22. Nine traps, one each in Columbia, Dane, Dodge, Door, Fond du Lac, Grant, Iowa, Jefferson and Kewaunee counties, reported their highest count of the season. This week's largest capture was 48 moths near Barneveld in Iowa County. The cumulative total count to date is 1,133 moths in 44 traps, with 262 of those collected in the past week.

Based on the consistent flights recorded since mid-April and prevailing weedy, wet fields conditions ideal for oviposition as migrants arrived this spring, many fields are considered at high risk of black cutworm damage. Included in this category are poorly drained and low-lying fields, those next to areas of natural vegetation or with reduced tillage (especially soybean residue). The start of the primary damage period has been estimated for May 25 in south-central and southwestern Wisconsin, May 28 in the lower west-central area, and June 2 in the central region. Crop consultants and growers are advised to begin inspecting corn (including Bt hybrids) for leaf pinholes and other signs of feeding during early season stand assessment. Scouting a few days before estimated cutting dates is recommended. It is important to recognize that Bt hybrids containing the Vip3A, Cry1A.105, Cry2Ab2, and Cry1F proteins provide suppression of this pest, but the larvae can still cut young plants.

EUROPEAN CORN BORER - Emergence of the first spring moths may start in the next two weeks in advanced southern locations. Most overwintered larvae are in the pupal stage, a period which requires about 10 days to complete at average daily temperatures of 65°F. Degree day accumulations near Beloit and Platteville, currently the warmest locations in the state, are expected to reach the 374 units (modified base 50°F) needed for moth emergence by May 27.

SLUGS - Minor leaf feeding was observed in damp, weedy cornfields in Monroe and Vernon counties. Slugs may become an issue if fields remain wet, particularly in no-till or reduced-till systems with heavy residue and little soil disturbance.

WIREWORM - Current field conditions are very suitable for this soil pest, which can bore into the base of corn plants and destroy the growing point. It is not uncommon for both wireworms and black cutworms to occur in the same field at the same time. Accurate identification is important since rescue treatment for wireworms is ineffective once damage is observed.

TRUE ARMYWORM - Another sizeable capture of 77 moths was reported from Janesville in the past week, while nine other black light traps from East Troy to Marshfield also reported small flights. True armyworm flights sometimes precede larval outbreaks by 3-4 weeks. Growers can expect armyworms to begin appearing in fields by early June.

-- Krista Hamilton, DATCP Entomologist