Consider an insecticide seed treatment in fields with a history of wireworms. Pea leaf weevil is also an early-season threat to pea crops that can be controlled by seed treatment, but it has not yet been identified in Manitoba. Cutworms are another early-season insect pest. However, cutworms are not on the seed treatment label and peas have the ability to re-grow following damage.
Pea aphids can be a sporadic pest in Manitoba. Scout for pea aphids at early flower. At four locations per field, check five plant tips (top 8 inches), or conduct 10 sweeps with a sweep net. If the economic threshold is reached (2–3 aphids/plant tip or 90–120 aphids/sweep), apply foliar insecticide at first pod to protect plants from feeding during pod formation and elongation.
Avoid fields with known infestations of perennial, biennial and/ or Group 2 resistant weeds such as cleavers, kochia, wild mustard and smartweed. Pre-emergent herbicide (PEH) is recommended, as peas are relatively poor competitors, especially early in the growing season. Yield can be reduced up to 25% by delaying weed control until four weeks after emergence. PEH options can provide excellent control of Group 2 resistant broadleaf weeds, which have limited in-crop control options (Table 2). Most broadleaf in-crop products perform best at the 2nd to 6th above-ground node stage and late application may result in crop injury and yield loss.
A minimum of four years between pea crops is recommended to minimize yield-limiting disease. Fields diagnosed with Aphanomyces euteiches should be cropped to peas only once every seven to eight years to reduce inoculum levels in soil.
To protect seedlings from common root rots such as Fusarium oxysporum, F. avenaceum and A. euteiches, use a fungicide seed treatment when planting peas in short rotations, or when soil conditions are cool, wet or compacted. Seed treatment will only provide effective disease control for up to three weeks after seeding, and neither seed treatment nor foliar fungicide will control mid-season infection of A. euteiches.
Mycosphaerella blight (Ascochyta pinodes) is the most prevalent and economically important foliar disease in Manitoba field peas. Symptoms include purplish leaf, stem and pod lesions that start as irregular flecks and may develop circular, concentric rings. It is often confused with bacterial blight, however the main source of inoculum is crop residue, not contaminated seed. Cool, wet weather and short rotations favour disease development.
Begin scouting at the 10th node stage and use the Fungicide Decision Worksheet for Managing Mycosphaerella Blight in Field Peas to determine your risk of yield loss due to Mycosphaerella. The first foliar fungicide application should occur at early flower. If infection continues to spread up the canopy and moist conditions persist, a second application can be made 10–14 days later using a different fungicide group.
Sclerotinia and downy mildew are found less frequently in field peas and symptoms are seldom severe. All pea varieties are bred with resistance to powdery mildew.