Phialophora gregata

Phialophora gregata is a deuteromycete fungus that is a plant pathogen which causes the disease commonly known as brown stem rot of soybean. P. gregata does not produce survival structures, but has the ability to overwinter as mycelium in decaying soybean residue.

Two strains of the fungus exist; genotype A causes both foliar and stem symptoms, while genotype B causes only stem symptoms. Common leaf symptoms are browning, chlorosis, and necrosis Foliar symptoms which are often seen with genotype A are chlorosis, defoliation, and wilting.

Brown stem rot of soybeans is a common fungal disease in soybeans grown in the upper Midwest and Canada. Brown stem rot (BSR) may commonly reduce yield of soybeans by 10-30% on susceptible varieties, up to 10 bu./acre in severe cases. BSR decreases both the number of beans per pod as well as bean size as a result of wilting, premature defoliation and lodging. In addition to decreasing yield, plants infected by BSR can be difficult to harvest due to lodging of soybean plants. University of Wisconsin Extension Field Crop Pathologist Damon Smith ranks brown stem rot as the third most important soybean disease in Wisconsin. Brown stem rot can impact most susceptible soybean beans in the north central states, especially during cooler late summer months.

There are many ways to manage Phialophora gregata. The most effective form of management is disease resistance. Crop rotation, tillage, SCN management, and changing the pH of the soil can also be effective.