Faba bean is a legume crop well-suited to cool and wet climates in Saskatchewan. These growing conditions allow faba beans to thrive and produce high yields. However, such conditions are also favourable for the development of many foliar diseases that can lead to significant yield and quality losses. 

One of the most prominent foliar diseases in faba bean-producing areas is chocolate spot, caused by the fungal pathogens Botrytis fabae and B. cinerea (Stoddard et al. 2010; Harrison 1988). Among the two, B. fabae is considered the more aggressive species (Harrison 1988). This disease has the potential to reduce faba bean yields by up to 71% (Sahile et al. 2008), particularly when foliar lesions become more severe during the flowering to early pod development stages (Tivoli et al. 2006). 

Preliminary results from an unpublished study by Dr. Syama Chatterton of Agriculture and Agri-Food Canada (AAFC) suggest that the most favourable conditions for the development of Botrytis spp. lesions are low dew point temperatures of around 5°C for several hours, followed by moderate nighttime temperatures of 10°C to 15°C. These conditions are less likely to occur in late June and early July, which is typically the recommended window for foliar fungicide applications during early flowering. 

While chocolate spot remains the primary disease of concern, recent disease surveys conducted as part of Dr. Chatterton’s study have identified a high prevalence of Stemphylium and Alternaria species in faba bean fields across Saskatchewan and Alberta. Currently, very little is known about the best control measures for these diseases or the extent of their impact on faba bean yields. 

Several fungicides are registered for use in faba beans; however, very few are specifically registered for the control of chocolate spot or other common foliar diseases. This limited availability can pose challenges for effective disease management, particularly under conditions favourable to disease development. 

Because faba bean disease development is heavily influenced by environmental factors, the timing of fungicide applications based on weather conditions is likely critical. However, this relationship between disease development and weather is not yet fully understood, and research on optimal fungicide timing in faba beans remains limited. 

To address this knowledge gap, a project was conducted over the 2022, 2023, and 2024 growing seasons to evaluate different fungicide timings in faba beans. The study took place at four Agri-ARM sites across Saskatchewan: Outlook, Yorkton, Melfort, and Scott. 

The main objectives of the project were threefold: to assess the effectiveness of late-season fungicide applications, to determine the optimal timing for a second fungicide application (if necessary), and to evaluate whether fungicide timing should be based on visible disease symptoms and/or weather events, rather than solely on crop growth stage. 

This was a two-part experiment, with treatment details outlined in Tables 1 and 2. Data collection across both experiments included tracking environmental conditions, recording the crop growth stage at each fungicide application, rating disease severity before each application, measuring the days to maturity, assessing grain yield, calculating thousand seed weights, and conducting an economic analysis. 

Key Findings 

Overall, disease levels were very low across most trial sites, with foliar disease severity remaining at or below 10%, even when June rainfall exceeded 100 mm. These relatively low disease pressures, combined with hot and dry weather during flowering and pod-fill stages in July and August, likely limited the effectiveness of fungicide applications. 

In cases where disease levels were higher, ranging from 30% to 60%, symptoms typically appeared later in the season. However, even under these conditions, no significant yield response to fungicide application was observed. 

Disease severity did vary at specific times. For example, at one site, a significant difference in disease levels was observed at the third disease rating (mid-July), and at two sites, differences were noted at the fifth rating (mid-August). Despite these differences, grain yield remained largely unaffected. 

Fungicide application only extended days to maturity in two site-years (17% of the time), and this effect was limited to late-season applications, typically 4 to 6 weeks after the bud stage. 

Although yield did not increase significantly with fungicide use at any site, seed weight improved in 50% of the site-years. In most of these cases, seed weight gains were associated with either a late fungicide application (2 to 6 weeks post-bud) or a dual application strategy. A single early application at the first bud stage increased seed weight in one instance; however, this effect was not repeated in other years or locations. 

Economically, the Outlook and Scott sites showed the most consistent positive returns from fungicide use. At Outlook, applications made 2 weeks post-bud (early to mid-flowering) generated positive net profits in all years. At Scott, applications made 4 weeks post-bud (late flowering to early pod) consistently resulted in a positive economic return, despite the lack of significant yield gains. 

These two sites—Outlook and Scott—also recorded higher levels of disease later in the growing season when averaged across all years (Figure 1), which may explain the greater likelihood of profitability. In contrast, profitability at the Melfort and Yorkton sites was low and varied significantly from year to year. 

Finally, in the second experiment, applying fungicide at the first flower stage—particularly when timed just before a weather event (e.g., late July to early August)—proved to be the most economically viable approach. 

Faba bean disease was relatively low at all participating sites in 2022, 2023, and 2024, with most sites reporting no disease to as much as 30-60% of the plants infected by foliar lesions, although higher infection periods were usually observed as the crop was nearing senescence. When disease ratings between treatments were significantly different, the difference between treatments was generally minimal (a 10% or less difference in foliar lesions), and such differences often did not occur until later in 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 higher with fungicide applications, but the increase was not statistically significant compared to the control. Because yields were frequently higher, applying a fungicide was usually economical; however, the general trend was that sites with greater rainfall during flowering had 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 economically feasible, late applications (late July) often yielded a positive outcome; however, the result was not significantly greater when compared to an earlier application at each site (late June to early July, depending on the site). As most sites experienced hot and dry conditions during crop flowering (July), it would be beneficial to conduct a similar study under wet and cool conditions during the crop flowering period. Most faba bean diseases thrive in cool and moist conditions, which were not experienced throughout the reproductive crop stages in this project.