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Corn
Volume 57 Number 9 Date 06/07/2012 STALK BORER - Surveyor reports indicate that 1-9% of edge row plants in several Grant, Green and Lafayette County corn fields are infested with small, ¼ -¾ inch larvae. This pattern of invasion is consistent with the stalk borer, a mid-season pest that migrates from perennial grasses and broadleaf weed hosts in early June and infests the first 4-6 rows of corn. As a reminder, Bt corn hybrids suppress but will not completely control stalk borers, so field scouting is strongly recommended through the V7 stage. EUROPEAN CORN BORER - The spring flight has peaked and is now declining in the southern half of the state. Larvae resulting from the flight are in the first and second instars and their characteristic shot hole whorl damage and windowpane feeding have been noted in a small percentage of corn fields. Surveys conducted in southern and central counties found very light infestations of 1-10% in 8 of 67 fields examined in the past week. The optimal treatment window for first generation corn borers has opened in the southernmost areas of the state with the accumulation of 800 degree days (base 50°F). TRUE ARMYWORM - Light injury was observed in 20 of 67 (30%) of corn fields sampled from May 31-June 6. Larvae ranged in size from ¼ -1¾ inches. This should serve as a warning for crop advisors and growers to continue inspecting corn and small grains for infestations. Treatment of corn is suggested when 25% of plants are infested with two or more small larvae (¾ inch or shorter) or 75% of the plants are infested with larvae of any size. BLACK CUTWORM - Economic infestations have been reported from Manitowoc and Sheboygan counties. A consultant in the area notes that 3-10% of plants were cut in several late-planted corn fields (less than 4 inches high) and treatments are being applied. The damage is ?spotty? and most of the cutting is occurring above the growing point on the smaller corn. Some of the treated fields are Bt hybrids, according to the report. As stated in previous bulletin issues, late-planted corn remains at risk of cutworm injury until the V5 stage. A rescue treatment is recommended if 3% of plants are damaged. --Krista Hamilton, DATCP Entomologist 
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