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Corn
Volume 64 Number 16 Date 08/15/2019 CORN ROOTWORM - DATCP's annual beetle survey is now in progress. Preliminary results from August 1-14 indicate populations are generally low for the third season in a row. Above-threshold averages of 0.75 or more beetles per plant have been found in only 14 of 165 fields (8%), while beetles were absent from 109 of the survey sites (66%). The current state average is very low at 0.2 beetle per plant. Corn producers should be aware of the potential for corn rootworm adults to redistribute from earlier silking fields to later-planted fields as beetle emergence continues. Now is the time to scout to determine this season's beetle pressure and to forecast the risk of larval root injury to continuous corn in 2020. WESTERN BEAN CUTWORM - Moth counts have declined at most monitoring locations. The trap in Green Lake County that captured 258 moths last week caught only 14 this week, and numbers at nearly all other sites fell below 10 per trap for the reporting period. The network's total weekly capture of 368 moths is a sharp decrease from 1,619 last week when the flight peaked at many locations. As of August 14, the state cumulative total is 3,422 moths in 57 traps (60 per trap average.) The highest individual count for the nine-week monitoring period is 401 moths near Princeton. Larvae produced by the annual flight are becoming evident in corn and have been noted recently in Adams, Buffalo, Columbia, Jackson, and Marquette counties. EUROPEAN CORN BORER - The treatment window for second-generation larvae will close next week in southern and portions of central Wisconsin. Final inspections should be performed before degree day accumulations surpass 2,100 (modified base 50°F) and larvae begin boring into corn stalks. Due to the variability in corn borer development across the state, sweet corn growers are advised to scout fields carefully. The predominant larval stages found this week were the 2nd and 3rd instars. JAPANESE BEETLE - This insect is still common on silks in cornfield margins. The highest beetle pressure noted during August surveys has been in Eau Claire, Grant, Sauk, and Trempealeau counties in the southwest and west-central districts. As a reminder, a fieldwide average of three or more beetles per ear is considered high and may be a concern for fields not yet pollinated. CORN EARWORM - Small to moderate moth flights into Wisconsin continued, and larvae from migrants that arrived in July are appearing in the tips of corn ears. The pheromone trap high count for the period of August 8-15 was 80 moths at Beaver Dam in Dodge County. All other monitoring sites captured fewer than 27 moths. The earworm caterpillars noted this week in the west-central and central areas (Monroe to Portage County) were about 1-1½ inches long. Routine scouting should be maintained for fresh market and processing sweet corn. -- Krista Hamilton, DATCP Entomologist 
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