Soybean Aphid numbers increasing in north central Iowa.
Over the past eight days, Soybean Aphid populations in the Alexander, IA area have been increasing dramatically. I’ve been monitoring the aphid populations for the past several weeks and noticed a significant increase in numbers on August 6th. That day, I started to intensify my scouting methods and focused on soybean fields for Latham Farms especially. I adhere to the economic threshold of 250 aphids/plant on 80% of the plants through podset. In every field that I scouted on the 6th and 7th, I found populations to be below threshold. A few were in the 40-50% category but most were at 25% and less. In many areas, it was difficult to find individual plants that were at or close to threshold.
That changed drastically over the next 3-4 days! I started scouting again on Tuesday and was amazed to find all but one of the fields at economic threshold and that one was at 75%. Obviously, we made the decision to apply an insecticide to those fields and work began that next day. Over the past two days I’ve received similar reports from Latham production growers in our area and other farmers as well. It would appear that most soybean aphids in our immediate area will be treated with an insecticide soon if they haven’t been already.
One word of caution! If your soybean fields are not at threshold, don’t be tempted to spray an insecticide too quickly. I’ve already received several reports of farmers who went ahead and added an insecticide to their last application of glyphosate herbicide just because it was “convenient” to do it at that time. These farmers are now spraying an insecticide again to control the aphid population that exploded in the recent week. Essentially, when they sprayed the first time, they killed whatever beneficial insects were in their fields at that earlier time leaving the door wide open for aphids from the neighboring fields to infest theirs!
By the way, over the years I’ve developed my own method of speed scouting for Soybean Aphid. If you’re having trouble following other methods, contact me and I will explain what I do.