Seeding date, temperature, and seed treatment affect pythium seedling blight of field pea

Abstract

Pea root rot and seedling blight caused by Pythium spp. often result in poor seedling establishment and patchy stands. Laboratory and field trials were conducted to determine the role of soil temperature and seeding date in the severity of these diseases, since weather records indicate a gradual increase in mean soil temperature from 4.5 to 17.3°C over the April 15 to June 15 planting season. In a gradient plate test to assess the impact of temperature on infection of field pea seedlings, the optimum temperature for infection was 15-22.5°C for a strain of Pythium ultimum and 17.5-27.5°C for Pythium irregulare. Field trials, conducted from 1994 to 1996 at Westlock, Alta., and Saskatoon, Sask. using a mixed inoculum of Pythium irregulare and Pythium ultimum applied in the seed row at seeding, showed that inoculation consistently reduced emergence and yield relative to the untreated control. There were few differences in emergence or seed yield between the seeding dates in late April to mid-May, but emergence was 10-15% lower and seed yield was 20-50% lower when the crop was seeded in late May to early June. There were no seeding date x inoculation interactions at any site. We conclude that low soil temperatures do not increase the severity of pythium root rot and seedling blight in field peas and that the crop should be seeded early on the northern prairies to maximize yield, even where soils are infected with Pythium spp. Seed treatment fungicides generally improved seedling emergence and decreased root rot severity relative to the inoculated control, especially with metalaxyl. Metalaxyl and thiram + carbathiin produced 15-50% higher seed yield than the inoculated control.

Keywords:

• epidemiology
• metalaxyl
• fungicide
• Pythium
• Pisum