Varying the timing of insecticide application limits non-target impacts in soybean
Varying the timing of insecticide application limits non-target impacts in soybean
Monday, March 10, 2014: 10:18 AM
Council Bluffs (Des Moines Marriott)
The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae) is an economic pest of soybean in North America, and is primarily managed with synthetic insecticides. Synthetic insecticides, however, are not available to organic farmers. Current management strategies available for organic farmers include host-plant resistance, conservational biological control, and a limited number of natural insecticides. Pyrethrum is approved by the USDA for certified organic farms, but degrades rapidly in sunlight. Our goal was to determine if there was an optimal time of day to apply pyrethrum that reduces both photo-degradation of the active ingredient and its impact on natural enemies. We selected four time points, 6:00 AM, 12:00 PM, 6:00 PM, and 12:00 AM, to apply pyrethrum. Aphid populations were measured at mid-day once a week from July through August, including the days following insecticide applications. We did not observe a significant effect of pyrethrum on soybean aphid abundance, however we did see numerically fewer aphids on plots sprayed at 12:00 PM and 6:00 PM compared to 12:00 AM and 6:00 AM. Pyrethrum significantly reduced natural enemy abundance only at 12:00 PM, where populations of Orius insidiosus and Coccinellidae were reduced. Based on these data the best time to apply pyrethrum is in the late afternoon (6:00 PM) when aphid populations can be effectively reduced without impacting the natural enemy community.
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