Issue No. 20, Article 3/August 26, 2011
ISA-Sponsored Surveys of Illinois Soybean Fields Reveal No Brown Marmorated, Red Banded, or Red Shouldered Stink Bugs
During the last week of July and second week of August, soybean fields in 47 Illinois counties were surveyed--thanks to financial support from the Illinois Soybean Association--for a variety of insect pests. Fortunately, we encountered no brown marmorated, red banded, or red shouldered stink bugs. I suspect that survey results will differ over the next several seasons, especially for the brown marmorated stink bug.
Within each county, five soybean fields were randomly selected, and 100 sweeps were taken in each field. Insects most commonly found were Japanese beetles and green cloverworms. Densities of Japanese beetles were greatest in Woodford and Bureau counties, with 48.2 and 33.2 beetles per 100 sweeps, respectively. Green cloverworms were numerous in Clay County (20 per 100 sweeps), Crawford (24.4), Douglas (43.4), Edwards (45.2), and Jasper (52.4). Green cloverworms are defoliators, and the economic defoliation threshold of 20% between bloom and pod fill used for a variety of soybean insects applies to treatment decisions for green cloverworms as well.
Western corn rootworm adult densities were very low in soybean fields across Illinois. Numbers were highest in Ford County (25 adults per 100 sweeps), the so-called epicenter of the variant western corn rootworm. In Iroquois and Vermilion counties, densities of western corn rootworm adults were 4.2 and 9.4 per 100 sweeps, respectively. Elsewhere in the state, densities were most often less than 1 adult per 100 sweeps. These data, along with those shared previously for cornfields (issue 18, August 5), further verify the overall low statewide population of the western corn rootworm in 2011. This should not diminish the fact, however, that severe corn rootworm damage has been observed in some fields located in northwestern Illinois planted to Bt hybrids expressing the Cry3Bb1 protein.
I offer my thanks to Ron Estes and Nick Tinsley, both with the Department of Crop Sciences, for their generous cooperation with this statewide survey.--Mike Gray