Common root rot of pea (Pisum sativum L.): Oat pre-crop and traffic compaction effects in fine-textured mollisols

Common root rot of pea caused by Aphanomyces euteiches Drechs. is widespread and difficult to control. In many production areas, yearly losses have been estimated at 10% because of the disease. Cultural control is needed even when disease tolerant cultivars are planted. Soil compaction due to traffic is known to aggravate the disease. In a series of research studies in a heavily infested nursery and adjacent farm fields, it was shown that compaction aggravates the disease by decreasing drainage and thus providing more favourable soil water conditions for early infection of pea roots. Traffic compaction has also provided an adverse abiotic environment for plant stress due to poor aeration. A precrop of oat (Avena sativum L.), as a full-season or late-summer crop, suppressed the disease only if the oat residue was incorporated at a shallow depth late in the fall using a chisel. Incorporated oat residue reduced inoculum potential of A. euteiches above 10 cm when incorporated with a chisel and below 10 cm when incorporated with a moldboard plow. A rolled towel bioassay using a susceptible pea cultivar successfully estimated inoculum potential when the test soil was placed near the epicotyl of 7-day-old seedlings. Although A. euteiches is an aggressive disease, all of these findings focus on vulnerability during the infection process. These investigations were required to examine carefully the soil ecology pertaining to the host crop, the pathogen when in the saprophytic mode, and the host crop interaction with the pathogen.