This is Dr. Nathan Mueller, your local agronomist with Nebraska Extension for Dodge and Washington counties. Over the past two weeks, soybean aphids have started to infest fields in Dodge and Washington counties. Based on my observations, soybean aphids populations are still low and do not warrant treatment. However, I want to discuss with you some guidelines moving into the second half of August incase populations increase.
First, there is three numbers I want you to remember 250-80-6. These are the numbers to remember when deciding if you need to spray for soybean aphids. The economic threshold is 250 aphids per plant on greater than 80% of the plants in a field with an increasing population prior to the full seed (R6) growth stage. This threshold is low enough to give you a 5 to 7 day window for an insecticide application to occur before economic injury. This is because aphids can double their population every 2-5 days.
Many soybean fields are currently in the R5 growth stage. It takes about 21 days for soybeans to mature from the beginning seed, R5 growth, to the full seed, R6 growth stage. The economic threshold at the early R6 growth stage is around 400-500 aphids per plant, instead of 250 used in early growth stages.
When scouting for aphids, you should check 20-30 random plants across of the field to get a good idea of aphid pressure. I know some soybeans are tall, partially lodged, or planted in narrow rows which makes is very difficult to scout, but do the best you can. Again, remember, the economic threshold is 250 aphids per plant on greater than 80% of the plants in a field with an increasing population prior to the R6 full seed growth stage.
For more information on determining your soybeans growth stage and scouting soybean aphids, please call me at 727-2775 or visit our local website at croptechcafe.org. Know your crop, know your tech, know your bottom line. This is Dr. Nathan Mueller, your local agronomist for Nebraska Extension on KTIC radio.