Reports have just come in of soybean aphids beginning to establish in the new growth of soybean foliage. Although there have been rumored fields over threshold and being treated, those contacting us (thanks to Troy Jenkins and Dan Childs) have only seen low numbers, but aphids are being found on the majority of the plants. This certainly indicates that scouting soybean fields should begin in earnest immediately. We are able to find aphids in many fields around Tippecanoe County, but again numbers are very low and have a lot of building to do to reach threshold before the R6 stage.
As stated in earlier Pest&Crop issues, aphids have been relatively scarce this year. Since numbers in the upper Midwest haven't flared, we don't suspect that winged aphids have migrated from those areas and descended on Indiana. To support that, those finding aphids are not seeing many with wings. The extreme heat last week and in the latter part of this week is not helpful for aphid survival and reproduction. They don't die as a result of the heat, but they do not reproduce very quickly at temperatures in excess of 90 degrees. It is likely that recent rains and more tolerable temperatures have spurred on the few aphids that lurked in the canopy unnoticed.
The rains have certainly encouraged new growth in soybean. That new growth is rich in nutrients that favor aphid fecundity and development. Soybean fields that are in the early R growth stages, especially in the northern counties, should be scouted soon. Concentrate on the backsides of new growth in the upper canopy and on the newly developing pods. Again, the vast majority of Indiana soybean fields have virtually no aphids in them. However, they are out there and some populations will be increasing and marching toward the magic number of 250 aphids/plant. Don't let your fields be among those that are not scouted until they are over threshold – take the time for a quick survey of 20 plants throughout the field.
Use the following treatment threshold guide determined by soybean growth stage: |