Soybean School: Slow growth impacts fungicide strategy

What's in store for the 2022 soybean crop as plants move through the vegetative and reproductive stages? Will it be a white mould year?
On this episode of the RealAgriculture Soybean School, BASF agronomist, Ken Currah, looks at the stark contrast between the 2021 and 2022 growing seasons and how it could impact disease management and fungicide strategies.
In late June 2021, much of the Ontario crop was at the V5 stage, fifth trifoliate, and growing quickly with a rapidly closing canopy. And then it started to rain and growers became highly motivated to apply a preventative white mould fungicide.
Fast-forward 12 months to 2022 and Currah is looking at a very different soybean crop as the calendar turns to July. "I'm really struck by how many sluggish soybean fields are out there," he says. The slow start can be attributed to a number of factors - from wet, difficult 2021 harvest conditions; to variable spring planting conditions with significant temperature swings; and high levels of corn residue.
When it comes to white mould, growers know their field histories and can easily identify high-risk fields, which will require fungicide treatment to suppress the disease. Managing moderate-risk fields, however, will become more of a challenge, says Currah. "It really is dependent on when the bean flowers, when those spores release, and when sclerotinia becomes available to infect the soybean plant."
The weather and field environment will also play a key role in determining fungicide strategy. Growers will need to be on the lookout for moderate temperatures, frequently overcast conditions and a damp soybean canopy once plants start flowering through the R1 to R2.5 stage. "In these moderate risk fields, growers will have to scout closely and use their eyes to determine what they need to do in these situations," adds Currah.
In the video, Currah reviews one-use and two-use fungicide strategies. In high-risk scenarios, growers can target application at the R1 to R2 stage. He adds that fungicide products with multiple active ingredients that work to suppress white mould are the best choice.
If disease-promoting conditions persist and high risk of white mould infection continues, Currah recommends a second application seven to 10 days following the first application at the R2 t0 R2.5 stage.
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