Pea-brassica intercropping does not ameliorate root rot in pea, but may provide yield or foliar disease benefits

Root rot, caused by a complex of soil-borne pathogens including Aphanomyces euteiches, Fusarium spp. Rhizoctonia solani and Pythium species, is a serious constraint to field pea production on the Canadian prairies. The only effective means of managing this disease are avoiding planting pea or lentil for at least 6–8 years and avoiding fields known to harbour high levels of root rot pathogens for the production of these crops. Growing a brassica crop as an intercrop with pea could, in theory, reduce the risk of root rot via the release of glucosinolates as brassica tissue decomposes. Glucosinolates break down into isothiocyanates, which interact with soil pathogens and help mitigate their impact. To test the effectiveness of pea-brassica intercropping as a root rot management tool, small plot field trials were conducted from 2018 to 2022 in Alberta, Saskatchewan and Manitoba. The Brassica spp. included canola; brown, hybrid and yellow mustard; and camelina. Root rot severity in pea was not reduced through intercropping; however, land equivalency ratio (LER) yield benefits were observed in some site-years. Additionally, at one site, the severity of mycosphaerella blight was reduced by intercropping with hybrid brown mustard. Although intercropping with Brassica spp. does not mitigate root rot in pea, it may still be considered a worthwhile practice due to its potential yield and foliar disease management benefits.