Historically, state-wide yield losses average 11 percent in years with wet springs and 8 percent in years with more normal planting seasons. The disease is most severe in poorly drained soils with high clay content. Traditionally, the northwest section of the state has had severe problems with Phytophthora root rot. With the increased use of no-tillage and reduced tillage residue management systems, however, Phytophthora root rot has become a serious problem in other areas of Ohio as well. Phytophthora root rot is the most important disease of soybean in Ohio.
Affected plants wilt and die in poorly drained areas of fields.
Symptoms Soybean plants are most susceptible to infection in the seedling development stage. Susceptible and tolerant varieties differ in the types of symptoms expressed following infection. On susceptible varieties, symptoms in young plants include rapid yellowing and wilting accompanied by a soft rot and collapse of the root and lower stem. More mature plants generally show reduced vigor and may be gradually killed as the growing season progresses. The root system is usually severely affected such that lateral and branch roots are almost completely discolored.