Reports of fields in Eastern/Central Ontario with threshold levels of soybean aphids have been coming in this week. Chris DiFonzo, MSU has also alerted us to very high numbers showing up in Michigan, especially in the thumb which could migrate here into Ontario via any future storm fronts. It is very important to be out scouting weekly from now until late R5 so that we can stay ahead of significant infestations.
Many fields within Southern Ontario have some low levels of aphids starting to show up, including those fields that have been treated with Cruiser. This is no surprise since Cruiser will no longer be present in the plant from 40 to 50 days after planting, right when the plants are entering the R1 stage when they are vulnerable to yield loss from aphids. In fact, studies are starting to indicate that the Cruiser treatment is having an adverse effect on some of our important soybean aphid natural enemies as they too are being exposed to the neonicotinoid insecticide. In an outbreak year, there is potential for Cruiser treated fields to have lower natural enemy populations compared to the untreated fields and may require a foliar spray sooner than the untreated fields would because of the reduced natural enemy population. This just adds to the list of reasons why we do not recommend the use of Cruiser seed treatment for soybean aphid control.
To help assess your soybean aphid populations and determine if you need to spray, I recommend you use the free Aphid Advisor app (www.aphidapp.com). It is currently available for Blackberry and iPhone users. We do not have an android version yet but hope to find some funding soon to add that too. A video on how to use the aphid app can be found here.
If you do need to spray, refer to Publication 812 for recommended products. I do not recommend the use of a neonicotinoid foliar insecticide (active: imidacloprid or thiamethoxam) on soybeans, particularly when there are flowers on the plants, as recent studies from Iowa State indicate that bees and other pollinators frequently visit soybean plants during flowering. These foliar neonicotinoid insecticides also have on the label the following statement: “Do not apply this product if following a seed treatment or soil application of a Group 4 Insecticide (neonicotinoids) within that season.”