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To spray or not to spray fungicide

June 20, 2016 - As the cereal crop's flag leaf stage approaches, many producers are wondering if a foliar fungicide application is worth their time and money.

"Most farmers want to know if they will get a yield and economic benefit from a foliar fungicide application," says Dr. Sheri Strydhorst, agronomy research scientist, Alberta Agriculture and Forestry, Barrhead. "Fungicide applications can be costly but, under the right conditions, can increase yields more than 30 per cent."

Strydhorst is leading a province wide-research project to help producers make fungicide management decisions. She says that, based on field research data from 2014 and 2015, they have come up with some helpful findings. "Our 10 site years of data show that a foliar fungicide application on AC Foremost wheat significantly increases yields when there has been at least five inches of rain from the time of seeding to end of June."

However, she cautions, it might not be that simple.

"For foliar diseases to infect crops and cause yield reductions, we need three things. First, we need a susceptible host. Second, we need the pathogen. Third, we need environmental conditions suitable for disease development.
"Our detailed foliar fungicide work was done with AC Foremost. It is an old cultivar that does not have the best genetic resistance to foliar diseases. Without the genetic resistance, this cultivar needs extra help to battle disease pressure."

However, not everyone is growing AC Foremost. In another study, Strydhorst found that Stettler wheat showed a yield increase with dual foliar fungicide applications in only one of nine site years; AC Foremost in seven of nine site years and AAC Penhold in four of nine site years. "Some cultivars are responding to fungicide applications while others are not."

This certainly complicates the decision making process, she says. "Producers should check disease resistance ratings on the cultivar they are growing. For example, AC Foremost is rated as susceptible to stripe rust and moderately susceptible to leaf spot while AAC Penhold is rated as moderately resistant to stripe rust and intermediate to leaf spot."

Dr. Kelly Turkington, research scientist at Agriculture and Agri-Food Canada, Lacombe, says that, "in a continuous wheat rotation, residue-borne diseases such as tan spot and septoria are likely present, so it is reasonable to expect a fungicide response with a susceptible cultivar the majority of the time, especially when the weather is favourable."

Strydhorst's research found yield increases with AC Foremost in response to fungicide applications when there was 1.9" of rain from seeding until the end of June. In this instance, winter wheat fields in the area were showing high levels of stripe rust. She says that with high levels of disease in the environment, fungicides can contribute to yield increases.

Turkington says each disease has specific conditions that favour development. "Stripe rust does not necessarily need a lot of moisture. Heavy dew can be enough to promote stripe rust. More rainfall facilitates inoculum production, dispersal (in the case of rain splashed pathogens) and host infection."

With the timely and frequent rainfall seen in much of the province, Strydhhorst suggests environmental conditions are right for tan spot and septoria pathogen growth.

"Our research shows that the more rain we have had, the bigger the yield benefit from the fungicide. For example, with 10" of rain from seeding until the end of June we observed a 26 bu/ac yield increase. But with 7" of rain the yield increase was reduced to 20 bu/ac. We still have one more year of research to conduct, but our initial findings suggest that more frequent and timely rains lead to bigger benefits from fungicide applications."

Turkington says stripe rust is a different pathogen and warm days with heavy dew resulting in several hours of leaf wetness per day can provide suitable environmental conditions for disease development in June. "However, rainfall and/or heavy dew in July can contribute to stripe rust development including on the head and peduncle also contributing to yield reductions."

While Strydhorst's research aims to simplify decision making, she says, as we all know, nothing is ever simple.

"At the end of the day, producers should assess: the disease rating of their cultivar, the presence of disease in their field and the environmental conditions. If you have poor genetic resistance, disease presence coupled with frequent, timely rains, it will likely be worthwhile to spray a foliar fungicide in 2016."

 


June 20, 2016
By Alberta Agriculture and Forestry

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