Phytophthora Root Rot of Alfalfa

Phytophthora root rot is a major cause of seedling death in newly established alfalfa and causes a progressive decline of established stands in Nebraska. This disease is caused by the fungus Phytophthora megasperma f. sp. medicaginis and occurs in most of the alfalfa producing areas in North America.

Phytophthora root rot is most damaging on susceptible cultivars and where the soil remains wet due to high clay content (heavy, fine-textured soils), poor drainage, over-irrigation or a combination of these. Phytophthora causes damping-off of seedlings, root rot, and rot of lower stems. It also weakens mature plants, making, them more susceptible to injury during severe winters and could eventually result in plant death.