It is worse on clay soils that retain water. P. halstedii overwinters as oospores in soil and as mycelium and sporangia in seed. Seedling are infected by zoospores from germinating oospores, leading to systemic infection. Sporangia are formed on all parts of infected plants. Sporangia are detachable.
Systemic infection leads to severe stunting and leaf distorion if infection occurs very early.
Other symptoms of systemic infection include chlorosis, development of superficial mycelium on lower leaf surface. Severe infection leades to seedling death. Plants which manage to reach maturity do not produce viable seed. Seedlings infected later show leaf symptoms but no stunting. Infection of older plants leads to club root but no foliar symptoms.