Volume 57 Number 10 Date 06/14/2012
EUROPEAN CORN BORER - Surveys this week detected minor infestations affecting 1-12% of plants in 6 of 38 fields checked. First- and second-instar larvae were the predominant development stages in the southern and central areas. Control treatments will become progressively less effective as boring into corn midribs and stalks begins next week. All corn fields in the southern half of the state, both non-Bt and Bt hybrids, should be inspected at this time.
STALK BORER - Larval infestations remain light in most corn fields, seldom exceeding 8%, and then primarily near field margins. An occasional field in Grant, Juneau, Richland and Sauk counties had injury rates of 6-11% in the first four edge rows, but significant damage was not expected since the plants were at the V6-V7 stages.
CORN EARWORM - The early migration of moths continued for the sixth week at the Janesville, Prairie du Chien and Ripon pheromone trap sites. Numbers ranged from 1-23 per trap, with the high count registered near Ripon in Fond du Lac County. Larvae resulting from the flight have not been observed as of June 12.
WESTERN CORN ROOTWORM - The University of Illinois-Extension reports that western corn rootworm beetles have begun emerging in central Illinois, nearly a month ahead of their usual July 4 date. According to the report, root injury has been documented recently in fields planted to Bt-rootworm hybrids expressing the Cry3Bb1 protein and large numbers of beetles are present at some of these sites. Resistance to the Cry3Bb1 protein among the western corn rootworm beetle population is suspected in Illinois and Wisconsin but has not yet been confirmed. Corn producers in Wisconsin can expect to see the first beetles of the year in 1-2 weeks and evidence of root injury later this month and in July.
--Krista Hamilton, DATCP Entomologist