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Management of leaf spotting diseases in winter wheat

McClintock was less susceptible to leaf spotting diseases and as a result, didn’t respond as well to fungicide applications. Photos courtesy of Agriculture,  and Agri-Food Canada, Melfort.
Osprey was more susceptible to leaf spotting diseases, and responded better to fungicide treatments.

Leaf spotting diseases can be a problem in winter wheat crops across the Prairies. However, there is little western Canadian information available for management in winter wheat. “As we started work on a larger winter wheat crop production project led by Dr. Byron Irvine at the Brandon Research Station a few years ago, we quickly realized the lack of management information for winter wheat leaf diseases in our area,” explains Dr. Randy Kutcher, plant pathologist with Agriculture and Agri-Food Canada (AAFC) in Melfort, Saskatchewan. “Although there have been studies on leaf spotting diseases in spring wheat, little had been done on winter wheat, so we initiated a project to find out more.”

The most important leaf spotting diseases impacting winter wheat crops are tan spot and septoria leaf blotch. In warmer conditions, spot blotch can also be a problem and powdery mildew can be observed in some years with the right climatic conditions. “Although leaf spotting diseases are considered in winter wheat breeding programs, they are not the highest on the list of priorities and therefore little rating information is currently available,” explains Kutcher. “Stem and leaf rust ratings are usually included for winter wheat, but leaf spot ratings are not. However, we do know that varieties vary a lot in their susceptibility to leaf spotting diseases.”

Kutcher and his team initiated this study to determine the benefit of varietal selection and various fungicide treatments to control leaf spot diseases of winter wheat across the Black soil zone of the Prairies. “We talked to breeders and looked at rust ratings of varieties to help select one of the best and one of the poorest varieties of winter wheat for leaf spot,” says Kutcher. “We selected McClintock, which was considered less susceptible to leaf spotting diseases, and Osprey, which is more susceptible. We also compared various fungicide products and timings of application to determine whether or not there were any differences or benefits to using fungicides on these varieties.”

A total of six site years of data was collected from trials at Lacombe, Melfort and Brandon between 2006 and 2008. Unsprayed check strips of McClintock and Osprey were compared to various fungicide applications at different timings. Some plots received one application of the various fungicides at the early stage or stem elongation, a second group of plots received one application of the various fungicides at the flag leaf stage and a third group of plots received various fungicide treatments at both timings. “The research showed some differences between fungicide products, but overall the popular fungicide products available all do a pretty good job,” says Kutcher.

In terms of timing, the fungicide products all performed well at the recommended flag leaf application stage. The split application showed marginal yield improvement in some of the trials but was not economical considering the extra time, work and expense involved for the second application. When required, using one application at the flag leaf stage with one of the popular fungicides is the best strategy. “We found the biggest differences between the varieties, with McClintock performing quite well,” says Kutcher. “We didn’t see huge yield increases between the unsprayed check strips and the strips where fungicides were applied to the variety McClintock. However, Osprey, which is a much poorer variety in terms of leaf spot, consistently showed a good response to fungicides over a number of site years.”

Leaf spot severity of the unsprayed checks was almost three times greater on Osprey than on McClintock. “Our research results show that growers in the Parkland or Black soil zones of the prairies will likely benefit from a fungicide application for leaf spotting diseases in susceptible winter wheat varieties,” explains Kutcher. “However, growers in the Dark Brown and Brown soil zones may not benefit as much.”

Although available information on the susceptibility of winter wheat varieties to leaf spotting diseases is limited, growers in the Black soil zone concerned about susceptibility should consider using fungicides. Growers will have to decide whether or not a fungicide is needed if they are growing a variety that tolerates leaf spot quite well.

Proper field scouting and past history of disease levels in winter wheat will be important considerations for growers, along with their geographic area. “Our experience from this research suggests that growers will see benefits from applying fungicides on poorer or more susceptible winter wheat varieties.”