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Stripe rust controls can still work despite potential increased tolerance to temperature

Stripe rust could show up with a vengence in Ontario again this year, but that doesn’t mean we’re lacking the tools to control the problem.

Last year was one of the worst stripe rust years that Albert Tenuta, field crop extension plant pathologist with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), has seen. Tenuta addressed the latest on where, when, and how often to apply fungicides to a room of farmers and agronomists at the Southwest Agriculture Conference, which took place Jan. 4 and 5 in Ridgetown, Ont. One of the diseases of focus was stripe rust and whether we can expect to see the same levels of the disease as last year.

Stripe rust typically thrives when temperatures sit around 16 C. But last year rust was exploding and multiplying in elevated nighttime temperatures sitting around 21 to 23 C. This may mean that the pathogen is changing in stripe rust.

“We’re seeing more and more races developing, becoming more heat tolerant,” Tenuta says. “They are living organisms that adapt and change, so nothing stays static over time.”

Since stripe rust is an obligate parasite (the disease needs a host to survive), the rust retreats back to the south in the U.S. in the winter, where there is greenery. With the milder winter last year, it’s likely spores are overwintering closer to Ontario, meaning the spores don’t need to travel as far and making it easier for them to reproduce. As millions and millions of spores are created, there are mutants that can develop and bypass resistance (from temperatures, for example) leading to an increase in cases of the disease.

If stripe rust had overwintered in the province, farmers would have seen it much earlier than the first reports in early May. This year, if conditions are right, we could potentially see the disease back in the province; it depends on the direction of wind as well as temperatures.

If the disease shows up again this year, there are two main ways for farmers to protect their crops. The first is well-timed application of fungicide. According to Martin Chilvers, assistant professor at Michigan State University and co-speaker at the session, in 2016 the most successful applications were the T2, or prior to flowering, applications. With applications at this stage, researchers were able to protect 20 bushels. Strobilurins and triazole compounds are best if applied as a preventative measure for stripe rust, although triazole also shows some post-infection functions as well.

Choosing a stripe-resistant variety is also important – even if it’s a moderately resistant variety. “Although you still see some disease developing, those lesions are often smaller, so they don’t produce as many spores,” Tenuta says. Therefore, spore production is reduced and successive generations decrease substantially.

But, Tenuta cautions, it’s still important to choose a variety that protects against Fusarium first and foremost. “Remember, Fusarium head blight is a risk you have every year. Stripe rust may occur – it may not.” Keep a lookout for stripe rust in your crops starting in May.