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Prevention not always the best bet

Sometimes, applying fungicide to durum as a preventative measure could increase disease

Better safe than sorry” is a mantra many producers live by. But in the case of durum, they might be better off ignoring it — at least when it comes to early and repeated fungicide applications.

Dr. Bill May, a Crop Management Agronomist for Agriculture and Agri-Food Canada’s Indian Head Research Farm, and Dr. Myriam Fernandez, an AAFC research scientist, conducted two studies between 2001 and 2006 looking at the effects of timing and number of fungicide applications on durum wheat productivity.

Rather than looking at economics, the researchers focused on the impact of management strategies on yield and disease incidence. “The main issue was that we wanted to see the effect of fungicide applications at different times on disease,” says Fernandez.

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The studies focused on triazole fungicides applied to test plots in southern Saskatchewan and western Manitoba. One of the studies, conducted in 2001 to 2003, looked at single and double fungicide applications at flag leaf emergence and flowering. The results were striking: while yields increased, early and repeated applications had a negative impact on grain quality and downgraded the crop.

“What we found in both studies was that an early application before or at flag leaf emergence in some cases increased yields, but based on conditions during the years of the studies, an application at the flowering stage was the most effective in terms of Fusarium head blight and leaf spotting, as well as kernel size,” she says.

Tank mixing cut rates of fungicide with herbicides for application at flag leaf emergence is a popular option for many producers.

But double applications of fungicide — at flag leaf emergence or earlier as well as at flowering — actually increased black point and red smudge in Fernandez’ and May’s studies. “We’re not saying that application at flag leaf would not be beneficial, but in those years conditions were not good for leaf spot development early on,” says Fernandez.

“The message that we want to get across is that repeated and early applications of fungicide might not be beneficial and could actually increase diseases of the kernels. Applying fungicide as a preventative measure is not effective.”

Avoid “canola model”

May says producers have gotten used to the “canola model” of pushing yields by increasing inputs, but this isn’t an effective strategy when it comes to most other crops, including durum.

“You’ve got to be cautious, because not every crop responds to inputs the way canola does,” he says. “I think each crop is different and you need to find the right set of agronomic tools for each crop.”

May’s and Fernandez’ study reports that fungicide application, whether single or double, was only observed to be profitable in the presence of higher disease pressure under conditions favourable to the development of disease.

“Our results also show that early fungicide applications might have a negative impact on dark kernel discolouration,” they write. “Percentage kernel discolouration, such as black point and red smudge, especially in the early application treatments, would have resulted in downgrading of durum wheat grain.”

Researchers are not entirely sure why discolouration can result from early fungicide applications, but Fernandez says the main reason is that greater kernel size resulting from fungicide applications would result in more open glumes which facilitates fungal penetration and infection.

May says actual disease pressure justifies fungicide applications, but producers need to be aware of the risks. “I think growers need to be aware that there are risks from applying early and often. I think the perception might be out there that it doesn’t matter how many times you apply, there’s no downside. But I think there is a downside,” he says.

“Sometimes with durum you have to control Fusarium because it’s the main downgrading factor, but in our environment, one application at anthesis will control leaf spots 90 per cent of the time so you’ll get that coverage if you have leaf disease incidence.”

Fernandez emphasizes that producers should be careful to avoid overusing fungicides to minimize the risk of resistance developing in pathogen populations.

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Julienne Isaacs

Julienne Isaacs is a Winnipeg-based freelance writer and editor. Contact her at [email protected]

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