Stripe rust control in spring wheat
For susceptible and moderately resistant varieties sown in mid-May, a foliar fungicide application at mid-anthesis will help preserve yield and quality. When susceptible and moderately resistant varieties are sown in early June in central Saskatchewan, fungicide application at stem elongation or mid-anthesis was equally beneficial for yield and quality factors.
Stripe rust, caused by Puccinia striiformis f. sp. tritici, has been observed frequently on the Prairies over the last several decades. Major epidemics in western Canada caused yield losses of up to 35% in two major epidemics in 2006 and 2011. The disease is primarily managed through a combination of resistant varieties and the application of foliar fungicides.
A research study was conducted to assess the fungicide application timings on spring wheat cultivars at two seeding dates in central Saskatchewan from 2012 to 2016. The research sites included the Bayer-Crop Science research farm at Pike Lake from 2013 to 2016, at the University of Saskatchewan East Sutherland Crop Research Farm Saskatoon from 2012 to 2016, and at the Melfort Agriculture and Agri-Food Canada research farm in 2013 and 2014.
Three wheat varieties were no-till seeded at two timings: mid-May and early June. The wheat varieties selected represented a range of genetic resistance to stripe rust, and included ‘AC Barrie’ susceptible (S), ‘CDC Imagine’ – moderate resistant (MR) and ‘Lillian’ – resistant (R). Seeding rate targeted a plant population of 25 seeds/ft2 (250 plants/m2). Fertilizer was applied according to soil test recommendations, and herbicides were used to control broadleaf and grassy weeds.
The foliar fungicide Folicur 250EW (tebuconazole) was applied at label rates. Application timings were stem elongation (GS31 of the BBCH scale); mid-anthesis (GS 63); early milk, (GS 73); a multiple application treatment that included applications at all three stages (GS 31, 63 and 73); and an unsprayed control.
Disease severity was assessed on the flag and penultimate leaves of 10 plants at the soft dough stage (GS 85).
Site-years were classified as either high severity where the susceptible cultivar AC Barrie had disease severity ranging from 60% to 100% for the mid-May seeding date (6 site years) and from 60% to 97% for the early June seeding date (5 site-years). Low severity site-years were less than 13% for the mid-May seeding date (6 site-years) and less than 10% for the early June seeding date (6 site-years) with the susceptible cultivar.
This summary will focus on results from the high severity site years.
Fungicide application beneficial under high disease pressure – mid-May seeding date
Stripe rust severity was very low for all fungicide treatments for the resistant cultivar. There was no benefit to any fungicide treatment and the severity in the unsprayed control for Lillian was 1.3% which was statistically similar to all of the fungicide treatments. There was also no yield differences between the fungicide treatments and the unsprayed control, averaging around 69 bu/ac (4075 kg/ac).
High stripe rust severity site-years, effect of wheat cultivar and fungicide application timing on stripe rust severity, test weight and yield at the mid-May seeding date.
Source: Vera and Kutcher. 2025
At the high severity site-years, foliar fungicide application on the susceptible variety (AC Barrie) reduced severity from 87.3% in the unsprayed treatment to 58.3% when applied at stem elongation and to 26.3% at mid-anthesis. However, when the fungicide was applied at the early-milk stage, severity was statistically similar to the unsprayed control at 77.4%. The multi-application treatment had the lowest severity at 11.4%.
Fungicide treatments were also beneficial for the moderately resistant cultivar (CDC Imagine). The unsprayed control had a stripe rust severity of 54.4% and was reduced to 28% when fungicide was applied at stem elongation, to 14.3% at mid-anthesis, and to 4.2% for the multiple application.
For the unsprayed susceptible variety, yield was 41 bu/ac (2733 kg/ha), and applying a fungicide at stem elongation increased yield by 32% to 54 bu/ac (3595 kg/ha). Application at mid-anthesis had statistically similar yield as the multiple application yield at 73 bu/ac (4911 kg/ha) for the susceptible variety.
For the moderately resistant variety, the unsprayed treatment yielded 44 bu/ac (2966 kg/ha). There were no yield differences for fungicide application at stem elongation, mid-anthesis or early milk. The mid-anthesis yield of 58 bu/ac (3914 kg/ha), the highest of the three fungicide timings, was statistically similar to the multiple application yield of 63 bu/ac (4248 kg/ha).
For thousand kernel weight, test weight and protein content, similar trends were observed for application timing on the three cultivars.
Early June seeding had similar results
Disease severity for early-June seeding at the high disease pressure sites followed similar trends as the mid-May severities. Again, disease severity for the resistant variety was very low, and there was no benefit to fungicide application on yield or quality.
Fungicide application at stem elongation or mid-anthesis provided yield benefit over the unsprayed treatment for the stripe rust susceptible variety (50% yield increase; average of both fungicide treatments over the unsprayed treatment). For the moderately resistant variety the trend was similar to the susceptible variety, however, the magnitude of the yield benefit was much less (14%). For the moderately resistant variety, neither of these fungicide treatments differed statistically from the unsprayed treatment.
Overall, the use of resistant varieties should be the foundation of stripe rust control in spring wheat varieties. For susceptible and moderately resistant varieties sown in mid-May, a fungicide application at mid-anthesis will help preserve yield and quality. When susceptible and moderately resistant varieties are sown in early June in central Saskatchewan, fungicide application at stem elongation or mid-anthesis was equally beneficial for yield and quality factors such as TKW, TW and protein content under high stripe rust severity conditions.
Funding by the Agriculture Development Fund of the Saskatchewan Ministry of Agriculture, Bayer CropScience and the Natural Sciences and Engineering Research Council (NSERC) of Canada Collaborative Research and Development is acknowledged.
Jenny Tatiana Vera & Hadley R. Kutcher (02 Jan 2025): Resistant wheat cultivars and fungicide applied at stem elongation or mid-anthesis are effective stripe rust control strategies in Saskatchewan, Canadian Journal of Plant Pathology, https://doi.org/10.1080/07060661.2024.2440408
Photo by Jess Schemenauer
