When does it pay to apply fungicide to Faba Beans in Saskatchewan and what does the weather have to do with it?

A project was initiated during the 2022 season to evaluate different fungicide timings in faba beans at four locations in Saskatchewan. The locations in the study included Agri-ARM sites at Outlook, Yorkton, Melfort, and Scott. The main objectives of the project were to determine the effect of late season fungicide applications, determine when a second fungicide application may be best, and determine if fungicide application timing should be based on visible symptoms and/or weather events rather than growth stage.

The first experiment consisted of 10 treatments with fungicide applications beginning at the first bud stage (R1) and continuing every two weeks until maturation of the faba beans or up to 12 weeks after first bud. Within the treatments, two had sequential or multiple applications of a fungicide at two and eight weeks after first bud and at two, six, and ten weeks after first bud. In the second experiment at Melfort only, there were eight treatments total consisting of a fungicide at first detection of disease, first flower, and prior to a weather event, along with three of the treatments using multiple fungicide applications at two weeks after first flower and first detection and at first detection and prior to a weather event. Data collection in both experiments consisted of environmental conditions, growth staging at fungicide applications, disease ratings prior to every fungicide application, days to maturity, grain yield, thousand seed weights and an economic analysis.

The conditions of 2022 were relatively hot and dry during the timing of fungicide applications at all sites (late June to mid August). Faba bean disease was relatively low at all participating sites in 2022, with most sites reporting as little as no disease to as much as 30% of the plant infected by foliar lesions depending on the disease rating timing. When disease ratings between treatments were significantly different, the difference between treatments was usually very small (10% or less difference in foliar lesions), and differences often did not occur until later into the season (late July to mid-August). Even when disease ratings were significantly different, they did not translate to a significant yield response.

Average yields were often greater with a fungicide application, but yields were not significantly increased from the control. Because yields were often greater, applying a fungicide was often economical, but the general trend was for sites with greater rainfall during flowering to have greater profitability when a fungicide was applied. Furthermore, although faba beans that were sprayed with more than one application of a fungicide often yielded greater, the cost of the second application did not result in enough of a yield response to make a dual application more economical than a single application. When a fungicide application was economical, late applications (late July) often resulted in a positive outcome; however, the result was not greater when compared to an earlier application at each site (Late June to early July depending on the site).