Taproot decline is appearing in more soybean fields at higher levels than in previous years based on recent observations in Alabama. Taproot decline is caused by the fungus Xylaria necrophora and was first detected in the mid-2000s in the southern United States.
Symptoms generally occur at pod filling stages (R4-R6) but can be observed anytime during the growing season. In some cases, symptoms can appear on seedlings and young, vegetative soybean plants. Yield losses approaching 25% have been reported from Louisiana. The fungus is thought to survive in soybean plant residue.
The disease is easy to spot in fields as infected plants will exhibit a yellow flagging in the upper canopy; plants will wilt and die soon after. Infected plants will break off at the taproot when given a firm tug.
Typically, the taproot and lateral root sections will be blackened due to the fungal infection. Incidence levels within fields in Alabama have been relatively low, typically well under 1% of plants in an infested field exhibit symptoms of taproot decline, however, incidence of the disease seems to be on the rise this year based on recent observations.
Differences in variety susceptibility to TRD have been observed in studies in the Southeast. Crop rotation and tillage may reduce survival of the pathogen but do not eradicate the presence of the disease. Currently, there are no fungicides labeled for TRD and resistant varieties are not available.
Contact Edward Sikora for more information.