42 It’s Farming. And It’s Better. Better Farming | December 2023 crops: the lynch fileS ‘GENETICS ARE YOUR NO. 1 DEFENCE’ Reviewing white mould in 2023 By Patrick Lynch There was a significant amount of white mould in 2023. I have been battling this disease since the early 1970s. In fact, I would get so frustrated with it that I ended up taking a holiday in the first two weeks of August. That was when growers started to see it and wondered what they could do. By that time there was nothing they could do and I became tired of telling edible bean growers that answer. You know all the common details. Disease spores fall on flowers or dead leaves. Flowers fall off and into the canopy. The infection spreads from these fallen petals on to the stems and then the disease spreads through the plants. There are some things that I learned: Abundant rainfall during infection period seemed to wash some of the mycelium from the plants and slow the spread of the disease. We saw many times that mould spread even without rain. If conditions were right, such as a heavy dew, this was enough moisture to allow the disease to spread. If you walked into a field at 11 a.m., and there was still dew on the leaves, the disease would spread. The disease needs about 12 hours of continued wetness to flourish. Working with edible beans has shown that genetics made a big difference. For soybeans, genetics also makes a difference. The No. 1 thing you need to do is pick a variety with good white mould tolerance. Planting a less than full season variety reduces mould severity. When soybeans were being widely promoted in Ontario in the late 1970s, the Ontario and Canadian government breeding programs had the best white mould-tolerant soybean varieties, better than the private breeding companies who were getting their genetics from the United States. Back then, white mould was not as big of an issue in the U.S. as it was in Canada. There is no hard reason why white mould took off in the U.S. during the 1990s. Reasons given include fuller canopies, a change in the pathogen and a change in genetics. Perhaps when the breeders went for higher yields, they dropped some genes that were giving mould protection. White mould was first noticed in 1948 in Illinois but was not a big concern. By the early 1990s, white mould was becoming a problem in Michigan, Minnesota and Wisconsin. That was when breeders started to select soybean genetics for better tolerance to white mould. Since then, private breeding companies have realized that soybean varieties with good white mould tolerance must be selected. Completely resistant varieties don’t exist, but some have less of a yield drop with a given amount of mould. Tillage can make a difference. If you don’t work the ground, the sclerotia will rot before they germinate. You can still get sclerotia germinating from deeper in the soil however even if you no-till soybeans. One thing you can do for the 20232024 season is to not work any ground that had serious white mould in 2023. The infected plants produced sclerotia and you want the sclerotia to rot on top of the ground. Sclerotia can live three to seven years in the soil depending on which research paper you read. They will reinfect susceptible crops like edible beans and canola. In fact, research papers indicate there are over 400 species that are susceptible to white mould. White mould will also infect many common White mould in soybeans. Patrick Lynch photo
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