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The NDSU Extension weekly podcast In the Pod: Soybean Updates delivers timely insights and expert advice on soybean production.
You're listening to In The Pod, Soybean Updates, a weekly trek into the latest soybean information from NDSU Extension. Today, we're talking about a fungus that can plague soybeans, white mold. What exactly is it? Where does it come from, and how do we spot it? Wade Webster, NDSU Extension plant pathologist, has the facts. Wade, when do soybean farmers need to start thinking about white mold?
Wade Webster:Yeah. So white mold on soybeans and many of our other diseases are very important around those flowering growth stages. So soybeans, we are thinking around that r one, which is the beginning of flowering until the r three, which is full flowering. Around this time, we're also thinking about canopy closure. And canopy closure is gonna be very important for the white mold fungus, what we call sclerotinia, to form those white mold mushrooms, which we call apothecia. And those apothecia have to form once we have canopy closure, we have cool weather, especially the nighttime hours. And so cool temperatures, we're specifically thinking around 55 to 65 degrees and consistent moisture. And if those environmental conditions are all present at the same time, those apothecia will form. And, again, that flowering period is most critical for when that infection occurs.
Bruce Sundeen:Why are the flowers so important?
Wade Webster:These flowers are very critical for white mold because it's essentially the food source of sclerotinia fueling that pathogen to get into the host, cause that initial infection, and start killing those plants. Inside those flowers are certain compounds called pectin. This pectin is very similar to what we use when we're making jams or jellies, and that pectin can serve as a very nutritious source of fuel for that pathogen. If those flowers are there, especially dead and dying flower tissue, these pathogens will be able to flourish. Again, if those spores are timed up with that flower tissue.
Bruce Sundeen:How long can white mold survive in a field?
Wade Webster:White mold survives is what are called sclerotia, and these are hardened structures. They kind of look like rodent droppings. And when these sclerotia are deposited into a field, they can survive for almost a decade. Now this is very important because even if we were to rotate out of soybeans, those sclerotia are still gonna be present. Now when we're dealing with other crops such as canola, dry beans, sunflowers that are also hosts for white mold, that just allows for new populations of these sclerotia to be rebuilt in those soils, in those fields, allowing that ten year cycle to start over again.
Wade Webster:Now what we've observed is that more susceptible crops have more white mold sclerotia produced leading to higher disease pressures in the following seasons. And these sclerotia, they are hard structures, and the only way that we can get rid of them are through a couple of biological products. A little bit of tillage can also help start to degrade these through the different microbes that are in the soil, and then we can also think about crop rotations, which are not always effective, but they can help to limit the amount of new sclerotia that are produced in that field.
Bruce Sundeen:Wade, when will we expect to see white mold?
Wade Webster:Yeah. So white mold is not a disease that appears immediately after infection. It is something that we have about a two to three week latency period in which that infection is occurring behind the scenes. One, if we were to cut open those stems, that fungus is growing in there, but we're not seeing dead and dying tissue yet. If we're seeing infection starting, say, early in July, we're not gonna start to see the disease of white mold with that fungal growth, dead plants until about the end of July or early August. So this is very important, especially when thinking about management strategies because these management strategies are not gonna be effective once we have the disease already developed. They have to be preventative. And when we talk about management and specifically fungicides in the next couple of weeks, we will talk about these in more detail about which products, the timing of these, and what we can do to best manage this particular white mold disease.
Bruce Sundeen:Thanks, Wade. Our guest has been Wade Webster, NDSU Extension plant pathologist. You're listening to In the Pod, Soybean Updates, a weekly trek into the latest soybean information from NDSU Extension supported by the North Dakota Soybean Council.