Distribution of root rot on pea and lentil crops on the Canadian prairies, 2016.

Wetter-than-normal spring seasons across large portions of the Canadian prairies in recent years have been associated with the emergence of root rot as a major constraint to production of field pea and lentil. Also, use of molecular diagnostic tools indicate that Aphanomyces euteiches Drechs. may be a more important component of the root rot complex across the northern Great Plains than previously thought. Therefore, a survey was conducted to assess root rot etiology, incidence and severity on pea and lentil across the Canadian prairies in 2016. Root samples were collected at 5–10 sites from 187 pea and 94 lentil fields across the region during flowering and sent to a central laboratory for assessment of visible symptoms (1–7 scale, 7 = dead) and DNA tests to determine the causal agent. On field pea, root rot symptoms were present in almost 90% of fields, with mean severity per field (3.2) slightly below yield-limiting levels. On lentil, incidence was >90% but mean severity was slightly lower (2.9). Differences among soil zones were generally small. Fusarium spp. and Rhizoctonia solani Kühn were detected in about 90% of fields, A. euteiches in >60% and Pythium spp. in about 50% of fields. A. euteiches was present at high levels in fields in every soil zone and was commonly associated with the most severe root rot symptoms. This study demonstrated that A.euteiches is a widespread and important root pathogen of field pea and lentil across the region.