Phytophthora Root Rot in Alfalfa

Phytophthora root rot lesions appear on alfalfa roots on seedlings and mature plants when the soil is saturated for several days and the soil temperature is above 60o F.  Most modern alfalfa varieties have good resistance to this fungus disease.  Improving drainage is the most important management action for avoiding this important disease of Oklahoma alfalfa.  This is probably the most important disease of alfalfa in Oklahoma.