A new tool is expected to be available soon to help Ontario soybean producers control soybean aphids while reducing insecticides, lowering production costs and minimizing negative environmental effects.The dynamic action threshold calculator developed by Rebecca Hallett, Yingen Xue and student Christie Bahlai at the University of Guelph in Ontario audits aphid numbers and their natural enemies to determine if insecticide application is necessary.The hand-held device comprises several disks: one that indicates aphid numbers, one for natural enemies and a third for the spray/no spray recommendation.It includes an aphid population growth model, which is based on temperature, natural enemy numbers and consumption ratesThe user counts the number of soybean aphids and natural enemies on 10 soybean plants, with the natural enemy numbers converted into natural enemy units.One NEU is the number of natural enemies that can consume 100 aphids in one day.The user lines up the arrow on the calculator with the number of aphids on the aphid disk and to the NEUson the NEU disk. The colour that appears indicates whether insecticide application is necessary.The recommended spraying threshold is 250 aphids per plant.“Natural enemies present in a soybean field can consume sufficient aphids to stop the populations from growing over the action threshold to the level at which economic injury is caused,” said Hallett.If no natural enemies are observed in the field, for example, it would be necessary to spray at 250 aphids per plant.If there are 450 aphids per plant and one ladybeetle found per plant, there is no need to spray because the beetles will consume enough aphids to stop aphid populations from reaching the action threshold.“And the fewer sprays used, the greater natural enemy populations ought to be in the field, thus providing even more protection from aphids and other pests.”Tests at three sites in 2009 compared the dynamic action threshold to the conventional threshold.“At two sites, no insecticide sprays were required in the dynamic action threshold plots, and aphids declined as a result of natural enemy populations. At the third site, the spray was delayed by one week relative to the conventional threshold plots.”In all cases, there were no differences between yield in conventional and dynamic action threshold plots.The principle of the DAT calculator could apply to any pest and natural enemy complex, Hallett said.
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