“Looking back at 2022, the overriding theme is that the state was still in drought, so there was low disease pressure for crops. The most dominant disease was late season root rot,” said Uta McKelvy, MSU assistant professor of plant pathology. “But what was interesting is that even though conditions were not conducive for diseases, we still saw increased samples of fungal leaf spot and wheat streak mosaic in small grains.”

As farmers are getting ready for the upcoming season, there are a variety of methods that can keep both yield-reducing diseases in check.

The first thing producers should be vigilant about addressing is wheat streak mosaic virus in small grains, especially because there is no treatment for the virus.

“Stopping the spread of any infection is important because this is a virus and there is no chemical treatment of any viral diseases,” McKelvy noted.

MSU recommends that farmers be active in the treatment of “green bridge hosts” or those offseason plants that can harbor the virus.

“Pre-harvest volunteer wheat is a very potent host, for example, as well as things like cheatgrass,” McKelvy said. “The virus is moved by wheat mites in the summer and can live in these kinds of hosts during the offseason. Farmers should spray the host plants and allow for at least two weeks for the hosts to die before planting.”

Another strategy to stop wheat streak mosaic virus is to delay planting, as in the case of winter wheat, until lower temperatures have killed off the mites.

“The mites are active in temperatures of 50 degrees and above. They also disperse in the wind like dust, so as long as the temperatures are high, the mites are active and can land on host plants,” McKelvy explained. “The warm fall of 2022 was conducive for the mites to disperse, for example, so waiting until the temps drop and kill the mites can help.”

Because there is no chemical treatment for wheat streak mosaic virus, keeping the virus at bay is a community effort, McKelvy noted.

“Your field could be a source for the virus, but you also want to think beyond the immediate border of your crop fields. If the virus spreads to a neighboring field, it can start to create a much bigger problem,” she said.

Fungal leaf spot

Another disease that producers should be on the watch for in 2023 is fungal leaf spot, despite the dry conditions.

“What diseases like fungal leaf spot need to grow is moisture and humidity, so it can seem like they won’t occur in a drought year but they can still appear, especially in areas with irrigation,” McKelvy said.

Preventing fungal leaf spot can be done by increasing the spacing between rows so air can move more easily through the plants. Timing when irrigation occurs and reducing seed density are also preventative options.

“Fungal pathogens like moist conditions and leaf wetness can allow the spores to germinate,” she said. “The fungus can also spread from leaf to leaf by water splashes, so the timing between irrigation can help reduce humidity in the canopy.”

Unlike wheat streak mosaic virus, there is a chemical fungicide treatment for fungal leaf spot, but McKelvy noted it is important to be sure that is the problem.

“It is important to make sure that it is fungal leaf spot before treating it. In the past two growing seasons, we had parts of Montana that looked like they had fungal leaf spot but the discoloration was actually due to a chloride deficiency in the soil,” she related. “So it won’t do anything to apply fungicide if that’s not the problem. With this fungus, there is also some time between the first observation of spots and when treatment is needed, so there is time to consult with your local Extension agent or the Schutter Diagnostic Lab here at MSU.”