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Corn
Volume 61 Number 16 Date 08/18/2016 CORN ROOTWORM - The map below summarizes the early findings of the 2016 corn rootworm beetle survey, completed in 155 of the expected 229 fields. Preliminary results show population increases in west-central and northwest Wisconsin and decreases in beetle abundance in the southwest and south-central regions. District averages thus far range from 0.4 beetle per plant in the south-central area to 0.7 per plant in the southwest. The state average as of August 17 is 0.6 beetle per plant. Economic populations of 0.75 or more beetles per plant have been recorded at 41 of the sites, or 26%. The highest average count of 3.4 beetles per plant was found north of Ripon in Fond du Lac County. The survey will be finalized next week. WESTERN BEAN CUTWORM - Larval infestations were observed this week in Adams, Chippewa, Dunn, Eau Claire, Juneau, Outagamie, Rock and St. Croix counties, where an estimated 1-7% of ear tips were infested with one or two larvae. Most of the caterpillars were in the intermediate instars and should enter the pre-pupal stage by before the end of the month. A few late moths are still appearing in black light traps, but the flight has effectively ended. Although the 2016 trapping survey documented the largest cumulative moth count in the last four years, this season's state total count of 1,528 moths in 75 traps (20 moths per trap average) ranks seventh in the 12-year history of western bean cutworm trapping surveys in Wisconsin. The record high count was 10,807 moths in 2010 (79 per trap) and the low was 521 moths in 2014 (five per trap). EUROPEAN CORN BORER - Second-generation larvae range from first- to fourth-instar in the southern and central counties. Larval infestations affecting 50-72% of the plants have been observed in a few later-planted corn fields, but most sites have lower populations involving less than 20% of plants. The treatment window for summer corn borers is expected to close statewide next week. Final management decisions for sweet corn must be made before the caterpillars have started boring into corn stalks and ears. CORN EARWORM - The early-August moth migration has resulted in minor infestations, mostly in western Wisconsin. Larvae ranging from ¾ -1½ inches were found this week in Eau Claire, Grant and Monroe counties, and egg laying is expected to intensify following the latest heavy moth flights. Sweet corn producers are strongly advised to continue monitoring traps and taking necessary treatment steps if warranted in the week ahead. Counts during the period of August 11-17 were: Arlington 421, Beaver Dam 30, Coon Valley 70, Cottage Grove 14, Hancock 0, Janesville 3, Madison airport 29, Marshfield 1, Mayville 92, Pardeeville 16, Prairie du Chien 3, Ripon 296, Sun Prairie 6, Sun Prairie North 13, and Watertown 0. -- Krista Hamilton, DATCP Entomologist 
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