Soybean Crop Update - July 9, 2021
As we struggle through a very wet week, we have arrived at a critical junction for the soybean crop. Most soybean fields are in early flower or close to flowering. The soil is saturated. The air is saturated for hours per day at 95%+ humidity. And the temperatures have cooled to high teens and low twenties. This is the definition of white mould infection weather. We are at a high risk currently for establishing white mould infection in early flowers in soybeans. I am equating this to 2014 risk level for mould and as you recall that was a devastating year for white mould infection. As fields dry and firm up it is critical to add a pass of fungicide to your soybean management plan. Based on Ontario soybean specific research your best options include Stratego Pro and Acapela. There is also a new product released from Bayer Crop Science called Delaro Complete that should provide solid suppression as well. As a reminder these products must be applied before infection begins. And they are rated as suppression only, so a second application is possibly necessary in 10 days.
For edible bean growers the risks are the same and the earliest fields have begun to flower with most of the crop expected to begin flowering the week of July 12th.
Secondly for soybeans we have been monitoring aphid pressure for roughly 4 weeks. There has been a steady increase in aphid pressure and populations are beginning to increase rapidly now. It is not difficult to find hot spots in fields with 500-1000 aphids per plant. Most “problem” fields are in North Wellington and North Dufferin counties. However, aphids can be found in all fields and have been reported widespread across the province. As we are now in the reproductive stages of soybeans the increasing populations become more critical and have the potential to impact flowering and pod/seed development. We have actioned several fields with insecticide, and I predict more widespread spraying by the week of July 19th. Aphid populations can double in 72 hours under ideal conditions. On the upside, I have often seen aphid populations crash too. Under wet conditions fungal pathogens can infect aphids and rapidly control populations. There is a fine line between too soon and too late for aphid control. Too soon and you may need a second pass. Too late and you risk significant stress on the soybeans leading to yield loss.
On the plus side we have newer options for aphid control in soybeans. Preferred products are Sefina from BASF and Sivanto Prime from Bayer. These products provide good, fast control of aphids, they provide approximately 3 weeks of control, and they leave the beneficials in the canopy to provide continued control later in the season.Photo taken by Matt Robinson, Agronomy Advantage Inc.