20 Story Idea? Email Paul.Nolan@Farms.com Better Farming | December 2023 Soybean disease With harvest complete, focus shifts to seed selection for the 2024 growing season and beyond. Looking back allows us to predict future crop performance. From a soy- bean perspective, we can learn lots from the 2023 growing season to help us succeed in the future. A little detective sleuthing will help us win big – solving crop-scene cases and achieving optimum yields. Mother Nature threw lots of curveballs at us in 2023. Excessive rainfall during critical periods, a cool start to spring, and ideal conditions for disease development led to an interesting year scouting fields and determining what was happening in the soybean crop. In my region, white mould was the main disease to contend with this year. However, we are seeing more soybean “white mould mimics” showing up in our area. Driving by fields and doing a simple scout from the driver’s seat, a lot of these soybean mimics look the same. Brown, dying/dead leaves within patchy areas of a field that look off- colour compared to the rest of the field were common this year. However, some “boots in the field” inspection would reveal that it was not always white mould that was the culprit, robbing us of top-end yields. So why was the 2023 growing season worse than some others? Simply put, the environment this year overrode many factors. If you have heard of the disease triangle, you know what I am talking about. With any disease, you need three factors for that disease to occur. Let us use white mould in soybeans as an example. You need a host (soybeans – or multiple other crops), you need a pathogen (white mould sclerotinia found in the soil), and you need the environment (wet soil conditions, humid canopy during flowering) for a disease to exist. In 2023, the environment played a huge factor and overpowered many soybean fields, increasing the odds of white mould showing up. Let us look at some key soybean diseases and their mimics. White Mould As the old saying goes, you need highyield environments to have white mould. White mould is a fungal disease that occurs during flowering, favouring cool, wet conditions and tall, lush soybeans that canopy quickly. As the disease progresses, tissues rot due to sclerotinia within the plant’s vascular system, leading to rapid wilting and dying. Keep in mind, when you see the “cottony toothpaste look” of mould on the plants, the initial infection occurred three to four weeks earlier. From the road, white mould necrotic leaves can look like other diseases mentioned below. Sudden Death Syndrome (SDS) SDS starts affecting soybean plants early in the growing season, but we do not see leaf symptoms until later. During the reproductive stages, the fungus produces a toxin that damages the leaves, causing interveinal chlorosis. The distinct yellow and brown necrotic areas between green midveins Paul Hermans photo TIME FOR SOME SOYBEAN DISEASE DETECTIVE WORK By PAUL HERMANS SOLVING THE CASE FOR DISEASE-FREE FIELDS & HIGHER YIELDS IN 2024
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