Yield loss and management of downy mildew on field pea in Alberta, Canada

Downy mildew of field pea (Pisum sativum) caused by Peronospora viciae f. sp. pisi has become widespread in the main field pea production areas of central Alberta. Field experiments were conducted at naturally-infested field sites over several years to assess the effect of seeding depth, seeding date, seed treatment and foliar fungicides on downy mildew incidence and severity, and to estimate the relationship between severity and yield loss. Downy mildew was shown to cause substantial yield loss on field pea. Even a moderately severe infestation reduced pod numbers by 65% and seed yield by 75%. The loss (pod number or seed yield) was best explained by a linear model (y = −2.3114x + 10.086; R2 = 0.9441 and y = −2.5165x + 10.378; R2 = 0.9533, respectively). Depth of seeding (range 3–7 cm) did not affect downy mildew. Similarly, seeding date (early, mid and late May) did not have a consistent effect on disease levels. Late seeding occasionally reduced downy mildew, but always resulted in low seed yield. Several seed treatment fungicides reduced downy mildew, and metalaxyl-based products produced the highest yield. Several foliar-applied fungicides, including pyraclostrobin, azoxystrobin and metalaxyl, reduced downy mildew severity, but the results were not consistent across years. We conclude that cultural practices may not be sufficient for effective management of downy mildew, and that metalaxyl-based fungicides applied as seed treatments or foliar sprays could represent the best control option until downy mildew resistant pea cultivars become available.

► Moderate levels of downy mildew reduced pod numbers by 65% and yield by 75%.
► Depth of seeding (range 3–7 cm) did not affect downy mildew.
► Seeding date did not have a consistent effect on disease levels.
► Metalaxyl-based fungicides are the best options for control of downy mildew.