The fungus survives in infested debris in the soil, but drops to low populations if nonhost are grown. Soybean is the only host for the brown stem rot fungus. Healthy stem on the right. The fungus produces spores that germinate, invade soybean roots, and progress into the vascular systems of soybean seedlings. The fungus remains restricted to the lower stem until the plant starts pod formation.
Infection occurs over a wide range of soil conditions.
Greater yield reduction often occurs when dry soil conditions prevail during at least part of the growing season. Vascular infection coupled with low soil moisture increases the water deficiency in diseased plants, leading to reduced pod fill and smaller seeds. However, yield losses may be reduced during years of high rainfall or optimal irrigation. The appearance and severity of foliar symptoms are also favored by dry soil conditions.