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Corn
Volume 62 Number 15 Date 08/10/2017


CORN ROOTWORM - The late-summer beetle survey is now in progress. Results from July 31-August 9 indicate populations are generally low across southern and central Wisconsin. Above-threshold averages of 0.75 or more beetles per plant were found in only 14 of 139 fields (10%), while beetles were absent from an unusually large percentage of sampled fields (68%). The current survey average is very low at 0.2 per plant. More rootworm adults are expected to appear on silks in later-planted fields as emergence continues, and scouting to determine this season's beetle pressure and to forecast the risk of larval root injury to continuous corn in 2018 should be conducted in the next two weeks.

WESTERN BEAN CUTWORM - Moth counts have declined at most monitoring locations. The trap in Columbia County that captured 101 moths last week caught 24 this week, and counts at nearly all other sites fell below five moths for the reporting period. As of August 9, the state cumulative total is 1,787 moths in 70 traps (25 per trap average), an increase from the 1,530 in 75 traps (20 per trap average) moths collected last season. The highest individual count for the nine-week monitoring period is 235 moths near Cambria. Larvae produced by the annual flight have been noted in in Adams, Columbia, Jackson, Marquette and Sauk counties. Infestations were light, with the exception of one noteworthy field in Columbia County in which an estimated 75% of the ears were infested with early-intermediate stage larvae.

EUROPEAN CORN BORER - The treatment window for second-generation larvae has closed near Beloit, La Crosse and Lancaster, but will remain open for 1-2 more weeks in parts of southern and central Wisconsin. Final inspections should be performed before degree day accumulations surpass 2,100 (modified base 50F) and larvae begin boring into corn stalks. Due to the variability in corn borer development across the state, sweet corn growers are advised to evaluate fields carefully and base control decisions on the specific conditions observed.

JAPANESE BEETLE - This insect is still common in the cornfield margins across much of the state. Beetles per ear were noted this week from Walworth to Eau Claire County. As a reminder, a field-wide average of three or more beetles per ear is considered high and may be a concern for fields not yet pollinated.

CORN EARWORM - Migrants continue to arrive in Wisconsin, but in low numbers. Counts during the past week ranged from only 1-6 per trap, with the highest number of moths registered in the Ripon area. The latest activity suggests the risk of egg laying remains low as of mid-August, though this could change before the end of the month. Regular scouting programs should be maintained for late-planted sweet corn fields.

-- Krista Hamilton, DATCP Entomologist