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Lessening the impact of Fusarium head blight in cereals

Investigating fungicide timing and other crop management options to address FHB.

March 20, 2024  By Donna Fleury


Barley fungicide timing trials at AAFC-Lacombe, July 2019. All photos courtesy of Kelly Turkington, AAFC-Lacombe.

In many areas across the Prairies, Fusarium head blight (FHB), caused by Fusarium graminearum, has resulted in widespread outbreaks in some years, resulting in yield and grade losses and deoxynivalenol (DON) contamination. Growers have some management strategies available; however, current solutions related to resistance, rotation and fungicides provide suppression at best. Researchers continue to investigate potential crop management strategies to lessen the impact of FHB in cereals.

“We initiated two companion studies in 2018 to investigate cropping strategies that could reduce the amount of inoculum and reduce the extent of host infection in both wheat and barley,” explains Kelly Turkington, plant pathologist with Agriculture and Agri-Food Canada and project lead. “For FHB management, the recommendation for producers over the last several years has been to use an integrated approach of applying fungicides, selecting varieties with resistance and following good rotations. However, even producers using those three strategies, particularly in northeastern Saskatchewan in high FHB years such as 2010, 2012 or 2016, were still significantly impacted by FHB. For many fields, the levels of Fusarium damaged kernels (FDK) lowered grades from CW#1 to #2 or #3 for wheat, and DON levels were often above the desirable level of about one ppm, depending on the wheat and barley end-use markets. Therefore, we wanted to investigate whether there were options to tweak fungicide application timing and other strategies that might help growers reduce FHB infection and crop losses.”

The objectives of the studies were to determine if row spacing (wheat only), water volumes (barley only), seeding rates and fungicide timing and their potential interactions affect FHB development, leaf disease and crop productivity in wheat and barley.

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For both the wheat and barley studies, trials were conducted at seven sites across Canada, including Lacombe (barley only) and Lethbridge, Alta.; Scott, Indian Head and Melfort, Sask.; Brandon, Man.; Normandin, Que.; and Charlottetown, P.E.I. Barley trials were conducted in 2018, 2019 and 2021, and wheat trials were extended into 2022. No trials were conducted in 2020 due to COVID-19 impacts.

Wheat fungicide timing trials at AAFC-Melfort, July 2022.

Water volumes included 20, 40 and 60 L/ac., and seeding rates of 200 and 400 seeds/m2 were compared. The fungicide trials compared Prosaro XTR fungicide applied singly just after head emergence at approximately one to two (barley) or three to four (wheat) days following full head emergence, or seven to 10 days later, or on both dates, plus a control with no fungicide application. Growers should note that these are research trials only, and some fungicide applications included are not currently registered on the label for commercial application. Producers must always follow currently registered products and label recommendations.

“We selected sites across Canada to be able to compare results from sites with higher levels of FHB and those such as Lacombe, where FHB is typically not a big problem,” says Turkington. “At many sites, the drought and weather conditions were not favourable for disease development, and although there wasn’t much FHB or DON at some of the sites, there was a lot of leaf disease. At all of the sites, we assessed FHB development as well as leaf disease, yield, thousand kernel weights and malting quality for barley. FHB is a very difficult disease to manage, with infection, FDK and DON levels all reflected by the disease triangle that requires three factors: the interaction of a susceptible host, a virulent pathogen and an environment favourable for disease development. These factors impact the main risk period for the crops.”

For FHB infection, the growth stage of the host is critical. Infection of the cereal head can occur anytime from head emergence to the start of senescence. Fungicide applications must be applied directly to the head tissue for protection. Therefore, if the fungicide application is made too early before all of the heads have emerged from the boot, some heads can be missed and become infected because the fungicide did not protect them. This makes managing FHB much more difficult and is why the level of control or efficacy when using a fungicide for FHB may not be as high compared to the expected efficacy for leaf disease fungicide applications.

“We studied barley and wheat in separate studies, and although we thought there might be some differences in FHB management, we observed similar results in both crops,” notes Turkington. “The results suggest that later single applications of fungicide and perhaps even dual post-head emergence applications may need to be considered to provide a more consistent and effective reduction in FDK and DON levels when FHB risk in cereals is higher. The dual timing tended to more consistently reduce DON and FHB levels in harvested grain. Ultimately, the weather conditions and spore load in the environment will dictate the ideal fungicide application timing, whether it is earlier timing or delaying and going a bit later.

AAFC plant pathology technician Jackie Busaan assessing Fusarium-damaged kernel severity in wheat samples from the fungicide trials.

“The dual and late application also showed trends of increased thousand kernel weights. This may result from maintaining the level of fungicide in that head tissue for a longer period of time, which leads to prolonged protection, better grain filling and higher thousand kernel weights. The later or dual applications may also potentially address fields with variable crop emergence. For example, if the FHB risk is high, one option may be to make one fungicide application when 75 per cent of the cereal heads have emerged, then go in and spray maybe a week or 10 days later to top up FHB suppression. Unfortunately, the current label indicates that fungicides for FHB can be applied up to when 50 per cent of the heads are in flower, which is likely about three days after full head emergence. In contrast, the late fungicide and dual timings in the current study would be outside of the current recommended label window for application.”

Turkington adds that some other research in the U.S. starting in 2013, and recent work at the University of Saskatchewan, supports the findings. For example, the U.S. studies trialled fungicide applications at two, four and six days after head emergence. The results showed that generally the later days didn’t compromise the level of FHB suppression, and depending on the location and year, the data suggests that six days after anthesis may be the better timing for fungicide application. The University of Saskatchewan trials in durum wheat also found that later-than-label recommendations can have potential.

Using integrated disease management strategies, like intercropping chickpea and flax, to manage foliar diseases can help reduce the risk of developing fungicide insensitivity.

“The results from the seeding rate trials showed higher seeding rates generally did increase emergence and often hastened maturity,” says Turkington. “Any practices that can help promote more uniform crop development and uniform head development help to present a more uniform target for the fungicide application. We also compared row spacings in the wheat trials and potential disease impacts of using either a narrow row spacing of seven to nine inches or a wider row spacing of 12 to 14 inches. Although research in the U.S. suggested there could be an impact, we did not see any impact in terms of disease development. Generally, grain yield was not affected by row spacing or seeding rate. The results of the water volume trials for barley did not show any real differences, although I would like to see the trials repeated when the FHB risk was much higher than we saw in our trials. We also monitored leaf diseases in the trials. The results show that if FHB risk is a concern and there are significant issues of leaf diseases earlier in the season, then two applications will be required, an early flag-leaf stage application for leaf disease and a second post-head emergence application for suppression of FHB and DON.

“This research and results from other projects in Western Canada and the U.S. have demonstrated the need for a label change for fungicide timing for FHB. The research shows that a fungicide application at the early start of the application window compromises the suppression of FHB symptoms. In a highly susceptible crop and environment where FHB risk is moderate to high, then later or dual applications would provide suppression of FHB and DON. However, these strategies are something that requires further research and potential changes in regulation and the fungicide product label in the future.”

Turkington is continuing this research and is collaborating with AAFC colleagues Hiroshi Kubota and Kui Liu at Swift Current on feed and malting barley projects to investigate PGR timing and fungicide timing. This work will provide the opportunity to further tweak strategies to manage FHB and DON through fungicide application.

At the same time, wheat and barley breeders are working hard to develop more resistant varieties and other tools potentially to mitigate the FHB disease risks. Finding crop management options to lessen the impact of FHB in cereals remains a priority. 

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