Oat diseases that affect your crop and what to do about them

Don’t let crown rust rob your yield

Following the announcement of plans to build a new oat mill in Manitoba last October, growers may be considering adding oats to the rotation. They’re a good cold-weather crop, prices have been decent and demand has been stable. Those adding oats to the rotation should be aware of the major diseases that affect both yield and quality.

While there are several diseases that impact oat, over the past 20 years crown rust has been the major one, says Randy Kutcher, a professor at the University of Saskatchewan. And while breeders put a lot of effort into developing new varieties with better resistance, the crown rust pathogen evolves and breaks down that resistance fairly rapidly.

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Rust fungi are obligate biotrophs with a complex life cycle, explains Kutcher. Their existence is dependent on living hosts, both oat, which is the primary host, and an alternate host. While they cause a lot of damage in oats, their sexual lifecycle takes place on the alternate host, a woody shrub called buckthorn, which tends to grow along rivers. Where the alternate host is present, growers will likely see crown rust more often and earlier in their oats. The disease usually ramps up around the end of July.

Crown rust fungi can also overwinter on oat residue. Come spring, the spores are released and infect the buckthorn. Then, the spores produced on the buckthorn are released and, once again, find nearby oat crops. If there is no alternate host, the inoculum will travel up from the United States. But where the alternate host is present, the spores will be released much earlier.

“If you don’t have the host, you have a lot better chance of containing the disease and reducing the variability, so you don’t get new races of the pathogen,” says Kutcher.

Crown rust-resistant and high-yielding varieties

Managing disease in oats begins with choosing the right variety. And while many growers still opt to plant AC Morgan — it’s an older, high-yielding variety — it’s also very susceptible to crown rust.

“We’ve had very good resistance in many of the varieties but in the old ones, the resistance is not effective anymore,” says Kutcher.

Many growers are happy to accept the risk in favour of yield advantage, but Kutcher says it’s not necessary. There are “very good varieties” coming out of the Crop Development Centre breeding program led by Aaron Beattie, he says. These varieties have good resistance to crown rust and they’re high yielding, Kutcher adds.

“Breeders have to keep up with new genes for resistance against crown rust,” he says. “They’ve been successful; there are very good varieties that you don’t have to spray.”

When to apply fungicide

Crown rust can dramatically impact yield in oats, sometimes taking as much as 50 per cent and up to 75 per cent of the crop yield in worst-case scenarios. It all depends on how early it strikes and whether or not the variety has resistance.

Epidemics tend to be worse when conditions are warm and wet. The disease damages the leaves, effectively reducing photosynthetic area. When the pustules erupt through the leaf surface, the plant also loses a lot of water.

“If you’re going to spray for it, you need to be out there in early July,” Kutcher advises. “Well before the panicle emerges, so by flag leaf for sure. Before the flag leaf would be better.”

Crown rust is also an issue in Manitoba, although the last major outbreak was in 2005. At that time, agronomists noted that some of the resistance varieties had was no longer effective. This indicates the pathogen has changed, says Manitoba Agriculture cereals specialist Anne Kirk.

Manitoba has been dry for the past few years, thus outbreaks have been minimal. Agronomists haven’t surveyed for the disease either, so while it is a disease that farmers deal with every year, it’s difficult to know if or where big outbreaks have occurred, says Kirk.

Millers usually offer recommendations for varieties, and those recommended varieties usually include a disease package, she says.

Other oat diseases include stem rust, leaf spot, barley yellow dwarf, smut and fusarium.

There are some leaf spot diseases that can be found in oats, but their impact is generally quite low, says Kutcher. “Usually, we don’t think they cause much yield loss, at least in Saskatchewan,” he says.

Stem rust is also possible, but breeders have it under control, he adds.

Barley yellow dwarf can be a problem in oats, although agronomists don’t really know how much yield loss it causes. While scouting is recommended, it is hard to predict and there is no treatment for the disease. Barley yellow dwarf will usually appear around late July.

“There’s not a whole lot you can do about barley yellow dwarf,” says Kutcher. “It seems to depend on the season whether the aphids spread it into the crop or not. It’s quite distinct in oats. You see quite yellow to red leaves that are highly infected on some occasions.”

Smuts are also possible, although Kutcher says he doesn’t see a lot in surveys. This is likely because of the use of resistant varieties and seed treatments.

Finally, there has been some concern about fusarium in oats. The nature of the panicle reduces concern. “You might see individual kernels or flowers that are infected, but it’s not as much of an issue as it has been in wheat,” says Kutcher.

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