Area of impact: Leaves and pods
Description: Small light green spots with raised centers develop on leaves. Tan or gray fungus grows on lower leaf surface especially in damp conditions. Spots can merge to form irregular brown patches. This can cause defoliation. Pods and seeds can also be infected.
Pathogen involved: Peronospora manshurica (a fungus)
Timing/Conditions: Can occur all season long particularly in damp warm weather.
Contributing factors: It overwinters on infected leaves and seed and is then transmitted by seed.
Management practices: Plant resistant varieties, use seed treatments, bury infested residue and rotate with a non-bean crop.