Aphanomyces root rot (ARR) of field pea (Pisum sativum), caused by Aphanomyces euteiches, can cause severe root damage, wilting, and large yield losses under wet soil conditions. To identify ways to manage this disease, the effect of A. euteiches inoculum density on field pea was studied under greenhouse and field conditions in 2015 and 2016. Increases in inoculum density reduced seedling emergence, root nodulation, and plant vigor, and resulted in increased root rot severity in both field and greenhouse tests. Seed treatments with the fungicides Apron Advance (thiabendazole + fludioxonil + metalaxyl) + Vibrance (difenoconazole + metalaxyl-M + sedaxane), INTEGO Solo (ethaboxam), BAS 516F (boscalid + pyraclostrobin), BAS 720F (metalaxyl + pyraclostrobin + fluxapyroxad), and BAS 516F + BAS 720F (3:1) were evaluated for their efficacy against ARR. All seed treatments except Apron Advance + Vibrance reduced root rot severity under controlled conditions. BAS 516F, BAS 720F and INTEGO Solo improved plant vigor and all treatments reduced seedling blight to varying degrees under greenhouse conditions, but not in the field. A collection of 22 pea genotypes was evaluated for resistance to root rot in field plot experiments. Line 00–2067 showed the least severe root rot symptoms, whereas ‘Spring D’ showed the lowest reduction in yield. The results suggest that there may be an opportunity to combine partial host resistance and fungicidal seed treatments to adequately manage ARR of field pea.

Field pea crops in central Alberta were surveyed for ascochyta blight from 2011 to 2012 and fungal isolates were recovered from foliar lesions on selected plants. Cultural and microscopic characterization of the 275 isolates obtained revealed that 272 were of Mycosphaerella pinodes and three were of Phoma medicaginis var. pinodella. Ascochyta pisi or Phoma koolunga were not identified. Isolates of M. pinodes were divided into two groups, GI and GII, based on visual assessment of culture characteristics. GI isolates (light to dark, mostly gray colony color; pycnidial distribution radial and concentric; conidia 10.5–14.5 × 4.2–6.2 μm most with one septum, occasionally two, constricted at the septum; spore mass light buff to flesh color) were predominant (83%), while GII isolates (dark to gray colony color; pycnidia abundant; conidia 8–16 × 3.5–6.2 μm most with 1 septum, constricted at the septum; spore mass light buff to flesh color) were less common (17%). The cultures of GII isolates were similar to recent descriptions of A. pisi, but they differed in spore color. In a host differential study, 13 pathotypes of M. pinodes were identified from 110 single-spore isolates. Pathotype I was predominant (88 isolates) and virulent on all nine differential genotypes. The other pathotypes (pathotypes Ⅱ–ⅩⅢ) were rare (1–6 isolates of each). Comparison of the present results with earlier studies suggests that pathotype I has been prevalent for many years, and that its aggressiveness on the host differentials has increased over time. Emphasis should be placed on breeding for resistance to M. pinodes in field pea cultivars intended for deployment in central Alberta.