Keep an eye on the soil temperature this spring to gain some insight into soybean water mould risks.
Michael Wunsch, a professor at North Dakota State University, says having some idea of where temperatures are and what the near-term weather may hold is key to understanding the issue. He was speaking at the recent 2018 BASF Knowledge Harvest.
“It’s all soil temperatures that define your risk window and obviously farmers are always at the mercy of the weather, but if you look at the long-range forecast, usually the temperature range is not too far off,” he said. “Rainfall is always a wild card, but it gives you a ballpark for air temperature and, with practical experience, you should be able to get an idea of what you anticipate for soil temperatures in that next two-week window when you hope that your beans are going to be emerging.”
Seed treatments for phytophthora may not be doing much during the average year in Manitoba, he warned. The researcher argued that phytophthora thrives in soil 15 C or above at seeding depth. For much of Manitoba, particularly as research examines earlier seeding dates, soil may not reach those temperatures through emergence, the period when Wunsch says seed treatment would be providing control. Instead, management strategies should centre on resistance when planting into cold soils, he said.
That knowledge will have little impact on seed treatment, he added. While phytophthora might not be a concern below 15 C, the same active ingredients are also used against pythium, a water mould that thrives in colder soils.
The Red River Valley is a prime habitat for that pathogen, Wunsch warned, pointing to the area’s clay-based soils and their tendency to hold water if saturated.
“Metalaxyl and mefenoxam have been on the market for a very long time,” he said. “They have efficacy against phytophthora and pythium, so they’re dual-purpose chemistries. If you’re below 15 C, you’re getting your greatest bang for your buck for pythium control and if you’re above 15 C, it’s giving you phytophthora control. If you’ve got poorly drained soil, you need protection against both of those, so you need a seed treatment, period.”
The change may come from any extra product the farmer may want to add, he said. If soils are expected to stay below 15 C and the farmer knows disease pressure is high for pythium, they may want to add a more pythium-targeted product such as ethaboxam to their management plan, he said.
The same holds true for soils that do hit that 15 C mark and are already under threat from phytophthora. Wunsch’s own research suggests that the relatively new oxathiapiprolin is stronger for phytophora control than pythium, he said. The chemical was approved for use in Canada for the first time this year.
However, the researcher also added that, “adding additional product only makes sense in those fields where you know that you really have elevated pressure.”
The 15 C threshold gave Jeanette Gaultier, BASF senior technical service specialist, something to think about after Wunsch presented the concept during BASF’s Knowledge Harvest event last month.
“It really does explain (things),” she said. “We do see later-season phytophthora in Manitoba, that’s what we see. We don’t see that early-season onset.
“Seed treatment is still a huge deal, but know what you’re targeting,” she added. “He had a really interesting message on that. You want something that covers off your pythium and your rhizoctonia and your fusarium and if it doesn’t cover phytophthora, it’s probably not a big deal here. I thought that was a pretty good message to growers and instead they should be looking at resistance in their varieties as a management technique.”
Variety selection has become a major area of interest for producers not only looking to manage disease, but to hit the balance between the safer short-season varieties and longer-season variety yield, she added.