Fusarium head blight in durum wheat
Summarized by Dr. Favaratto and Dr. Smyth based on Singh et al. (2021) research - Fungicide Mitigates Fusarium Head Blight in Durum Wheat When Applied as Late as the End of Flowering in Western Canada: "Fusarium head blight (FHB) is one of the most important diseases of durum, spring, and winter wheat in Canada. Growers rely on an integrated strategy to manage the disease, including fungicide application at the current recommendation of early to 50% anthesis (BBCH61–65). This study evaluated the effect of fungicide application timing and seeding rates of durum wheat on FHB. Field trials were carried out from 2016 to 2018 at three locations in Saskatchewan. Eight treatments of the metconazole fungicide Caramba were applied to durum seeded at 75 and 400 seeds m−2. The fungicide treatments consisted of a nontreated check, a treated check, and applications at BBCH59, BBCH61, BBCH65, BBCH69, and BBCH73 and a dual application treatment (BBCH61 followed by BBCH73). FHB index, proportion of Fusarium-damaged kernels (%FDK), deoxynivalenol (DON), grain protein content (GPC, %), and yield were evaluated. Seeding rates influenced all parameters. The high seeding rate had a higher yield and FHB index but lower DON and GPC than did the lower seeding rate. All fungicide treatments resulted in lower FHB index, DON, and %FDK than the nontreated check. Under FHB conducive conditions, all anthesis applications from BBCH61 to BBCH69 had a similar effect on FHB index, %FDK, DON, and yield, whereas in years with low disease severity, the application at BBCH65 had lower FHB index, %FDK, and DON relative to other single applications. The dual application (BBCH61 + 73) treatment resulted in similar FHB index levels, %FDK, and DON content as the BBCH65 application at all site years. Our results indicate that the window of fungicide application can be extended to the end of flowering when FHB risk is high."
Fungicide mitigates fusarium head blight in durum wheat when applied as late as the end of flowering in western Canada
Significance
Fusarium head blight (FHB) is a major threat to durum wheat in Canada, causing yield losses and contaminating grain with harmful toxins like deoxynivalenol (DON). The research, conducted over three years in Saskatchewan, investigated how seeding rates and fungicide timing influence FHB severity, grain quality, and yield. Researchers tested two seeding densities—a very low rate (75 seeds/m²) and a very high rate (400 seeds/m²)—along with fungicide applications at different growth stages, from early heading to early milk development. The goal was to determine the best strategies for farmers to minimize FHB damage while maximizing productivity.
Analysis
One of the most critical discoveries from this research is how precisely timed fungicide applications can dramatically improve FHB management in durum wheat. The study confirmed that fungicide application timing had a significant impact on yield, FHB index, Fusarium-damaged kernels (%FDK), and DON contamination, particularly under high disease pressure. When disease pressure was high—such as during the unusually wet season in 2016—fungicide treatments applied between the beginning and end of anthesis consistently reduced disease severity and toxin accumulation. Importantly, under these conditions, applications at 50% anthesis and late anthesis were equally effective, with no clear benefit of applying fungicide even earlier or later.
Interestingly, a single, well-timed fungicide spray at 50% anthesis increased yield by up to 37.5% compared with untreated controls. This was comparable to dual applications (beginning of anthesis + early milk), indicating that multiple sprays often did not provide additional benefit over one carefully timed application. The dual applications did result in the lowest FHB index in high-pressure conditions, but reductions in DON and FDK were not significantly greater than those achieved with a single spray at 50% anthesis or end of anthesis.
Under low disease pressure, fungicide applications still offered measurable benefits. For example, a single application at 50% anthesis reduced FHB index to about 2.9% compared with nearly 12% in the untreated check. However, yield differences were smaller (around 10% higher with 50% anthesis treatment), and DON levels were already low across all treatments.
Seeding rate had a major influence on crop performance and disease dynamics, however, optimum fungicide timing was the same at both seeding rates. The high seeding rate (400 seeds/m²) increased yields by as much as 31% due to greater plant density and more uniform crop stands. However, higher density also led to denser canopies and more synchronized flowering, which increased susceptibility to FHB when environmental conditions favored infection. This was reflected in higher FHB index scores under high disease pressure compared to the low seeding rate. In contrast, the low seeding rate (75 seeds/m²) promoted more tillering and variability in spike emergence, which tended to dilute infection pressure over time and reduce visible FHB severity. Paradoxically, however, this same spread in flowering windows led to higher DON levels, likely due to late-forming tillers becoming infected without obvious symptoms. This underscores that less visible disease (and lower %FDK) does not necessarily mean low toxin risk.
Seeding rate also affected end-use quality traits. The high seeding rate improved test weight (TW)—a key measure of grain density and quality—but tended to slightly reduce grain protein content (GPC). This is important in durum wheat production, where protein levels are critical for pasta-making quality. Fungicide treatments increased TW and thousand kernel weight (TKW) by reducing shriveled kernels associated with FHB damage. Notably, fungicide applications did not significantly affect protein content, suggesting they can enhance yield and kernel plumpness without compromising protein levels.
Conclusion
For farmers these findings suggest practical strategies including higher seeding rates around 300 seeds per square meter to boost yields while being prepared to apply fungicides when FHB risk is elevated. The most effective application window occurring during the 50% anthesis stage as a single well-timed fungicide application, which performed as well as multiple sprays; this is most cost-effective. Growers should track weather patterns and disease forecasts since FHB severity varies by year with fungicides providing the greatest benefits during wet high-risk periods. These suggestions are a scientifically validated approach to optimize durum wheat production by balancing yield and grain quality protection through disease management without overusing fungicides.