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Scouting for Aphids

August 3, 2009

soybean_aphidAlmost every soybean field out there has aphids in it. So how do you know if you have enough aphids to warrent spraying an insecticide? You spray when the aphid population exceeds the economic threshold, in the soybean aphid cases the economic threshold is 250 aphids per plant. The “old” way to scout for aphids was to count ALL aphids on 20 plants. If the majority of the plants had over 250 aphids an insecticide application was recommended. The University of Minnesota Entomology Department has created a more streamline aphid scouting method, they refer to it as “Speed Scouting”. This “new” method makes it a lot easier to scout for aphids. Basically, you have a chart and you count 40 aphids per plant. Once you hit 40 you stop counting and move on to the next plant. Here is an example of how this chart works . . . so you counted the aphids on 11 soybean plants, 10 of these plants had more than 40 aphids per plant, you look at the chart and it tells you to count five more plants, all five of the plants counted had more than 40 aphids per plant . . . the chart says you definitely need to treat, but you need to confirm that need in 3-4 days right before you spray by recounting 11 soybean plants and following the chart. One may think that this seems tricky. Once you have the chart this is real easy and requires alot less eye strain than the old method. Here is the link for the speed scouting chart

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