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Benefits of fungicides on soybeans

When white mould became an issue for Manitoba soybean growers in 2013, there were many debates about the benefits of fungicde

This past season was the first time in a number of years, probably since 2010, that white mould in soybeans has been an issue for growers in Manitoba. It raised all sorts of questions about the disease itself, management practises to mitigate infection and what fungicides are available to suppress or control the disease.

Dennis Lange is the crops farm production advisor with Manitoba Agriculture, Food and Rural Development. “I’ve been working with soybeans since 2011 for the department,” he says. “The 2011 and 2012 seasons both experienced hot and dry conditions in July and August and white mould was not evident. This past season saw cooler weather at the end of July with heavy dews and, as a result, conditions were ideal for white mould to flourish in both soybeans and edible beans.”

Alex Wahl is the owner/manager of GJ Chemical in Altona, Manitoba, in the heart of soybean country. “We heard from a lot of growers this year who were seeing white mould infections, as well as seeing it ourselves during our scouting activities,” says Wahl. “It was the weather that promoted the growth and development of the disease but it’s definitely a concern for a lot of guys going forward, mainly to get more information and understand its impact on the crop.”

Benefits from fungicides

Kristen Podolsky of the Manitoba Pulse Growers Association agrees with Lange that white mould has not yet been a noticeable issue for soybean growers. “Generally, our growers have seen more leaf diseases in soybeans,” she says. “However, fungicides are not widely recommended or used in these cases because they don’t seem to be of economic benefit.”

That didn’t fully answer the question: Does using a fungicide provide an added benefit or response?

“In all the research I’ve reviewed from Ontario and out of the U.S., there is an economic advantage about one-third of the time,” explains Podolsky. “This tells us that growers certainly do not want to spray in the absence of disease pressure, and if they do, the economic response is variable.” That’s for foliar diseases. The decision to spray for white mould is even more complicated, and more risky. “We should recognize that despite white mould pressure in soybeans this year, we still saw phenomenal yields, without spraying.”

The soybean plant itself is not as susceptible to damage from white mould as other broadleaved crops grown in the region. “Yield losses are not what you would think from looking at an infected field, which can look pretty ugly,” says Podolsky. “It seems the soybean plant is more tolerant of the infection than, say, edible beans or canola.”

Management practices

There are some management practices for soybean growers to consider if they are concerned about white mould or other fungal infections.

  •  Wide rows allow for more air circulation in the canopy versus solid seeding.
  •  Paying attention to the architecture of the plant — choosing an upright versus a bushy plant can be helpful as well.
  •  Managing fertility to prevent lodging can help with harvesting as well as reducing the potential for the development of disease.
  •  Paying attention to crop rotations and not putting soybeans after soybeans or close to edible beans or canola will help break the disease cycle.
  •  There is anecdotal evidence that there could be differences in susceptibility among varieties. However, varieties are not rated in registration or other trials for resistance to white mould so there is no scientific basis for these judgements.

Eric Phillips, product lead for fungicides and insecticides with Syngenta Canada, estimates that about 30 to 40 per cent of the U.S. soybean crop is getting some sort of fungicide application in season, primarily for leaf diseases.

“White mould is not a disease of major concern in the U.S.,” explains Phillips. “This is due to their growing environment not being conducive to its development.” The fungal disease of most concern in the U.S. is frogeye rust or Cercospora leaf spot. Globally, the most devastating disease in soybeans is Asian soybean rust.

In 2013, there was one product, Acapela, registered for suppression of white mould in soybeans in Western Canada. During 2013, but too late for growers to be able to use it, Allegro received registration for control of white mould in soybeans.

Two biological fungicides, Serenade MAX from Bayer CropScience and Contans from SipcamAdvan are also registered for the suppression of white mould in soybeans.

“The industry is still in the learning process when it comes to application of fungicides for control of white mould in soybeans,” says Phillips. “We recommend applying Allegro at the R1 or early bloom stage to R2 or full bloom stage, and if necessary to follow up 10 to 14 days later at R3 or early pod formation stage.” It is also important to use sufficient spray volumes to penetrate the canopy and get good coverage on the plant. †

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