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Relationship of Sweet Corn Silking Stage to Oviposition by the Corn Earworm 2001

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Project Leader: Richard W. Straub, Cornell’s Hudson Valley Lab., Highland NY

Cooperator(s): John Gill, Gill Corn Farms, Inc., Hurley, NY

Teresa Rusinek, Ulster County CCE, Kingston, NY

Type of grant: Monitoring, forecasting, and economic thresholds

Project location: Throughout the Northeast

Abstract: Corn earworm (CEW) is an annual pest of sweet corn in most of the Northeastern US and requires multiple applications of insecticides to manage below a threshold level. It is commonly believed that CEW do not oviposit (i.e., lay eggs) on sweet corn silks after they have dried. If true, insecticide treatments could logically cease at some predetermined time interval after pollination, because silks commence drying within hours of pollination. Problematic however, is that neither conventional wisdom, nor the historical literature, precisely defines the point at which silks are sufficiently dry to become unattractive for oviposition. We hypothesized that CEW cease to oviposit on silks that are 50% dried. Field experiments, utilizing silk dryness treatments ranging from 0% to 75% and methods to prevent oviposition before the silk dryness targets were attained, were performed during 2001 by which to better define a silk stage treatment threshold for CEW. Under high infestation pressure from CEW, results did not confirm our hypothesis, for 50% and 75% silk dryness treatments yielded 58.4% and 44.3% infestation of ears, respectively. Visual estimations of silk dryness however, correspond well to simultaneous measurements of % loss of silk wt. Possible reasons for the erroneous hypothesis are discussed.