Is There A Solution?
By Sherri Roberts PAg, Crops Extension Specialist, Weyburn
The acres of faba beans are increasing across the wetter areas of Saskatchewan and along with them comes the disease chocolate spot. It is regarded by plant pathologists as the most difficult disease of faba beans; Some, like Dr. Syama Chatterton, Lethbridge-based Plant Pathologist with Agriculture and Agri-Food Canada, stat it is actually the number one disease of faba beans in the world. Chocolate spot is a fungal disease caused by Botrytis cinerea and Botrytis fabae.
Dr. Chatterton, with funding provided by SaskPulse, is conducting a multi-year faba bean epidemiology chocolate spot research project in Saskatchewan and Alberta. So far, she’s found that chocolate spot incidence is negatively correlated with high temperatures and positively correlated to periods of high humidity and leaf wetness. She also has found that in Saskatchewan, that there are multiple infectious periods throughout the growing season, with the highest disease levels occurring towards the end of the growing season.
Currently, there are only two fungicides registered in Saskatchewan for use on faba beans for chocolate spot. The only problem is they are only for suppression, not control. Is there a cultural way that this disease could be managed? Intercropping studies done in countries where faba bean acres are much greater than Canada show some promising possibilities.
The effects of nitrogen management and intercropping on faba bean chocolate spot disease development studied by Guo in 2019, conclude that intercropping faba bean with wheat created a micro-ecological environment conducive to the growth of faba bean, which effectively reduced the occurrence of chocolate spot disease and increased the faba bean yield.
Intercropping cereals with faba bean has been proven to reduce plant disease incidence regardless of fertilizer input. Meta-analysis conducted by Zhang in 2019, quantified the disease suppressive effect of intercropping cereals with legumes at different levels of nitrogen fertilizer. Intercropping reduced disease incidence by 45 per cent on average. The disease reduction was greatest during the early stages of outbreaks.
While studies show there may be a cultural method to control chocolate spot in faba beans, Saskatchewan specific research will need to be done to see if this same result is achievable here. If you have any questions regarding intercropping, please contact the Agricultural Knowledge Centre at 1-866-457-2377 or your local crops extension specialist.