Overview

Soybean production in Ghana is often challenged by various diseases that can cause significant yield losses if not managed properly. Bacterial leaf blight, caused by the bacterium Pseudomonas syringae pv. glycinea, is one of the most prevalent soybean diseases in Ghana. The disease is most common following windswept thunderstorms in July and August, and it can cause up to 65% yield loss in soybean crops. Symptoms of bacterial blight typically develop several days after a rainstorm or hailstorm, and they are most evident on new growth that is expanding at the time of the rain event. The disease can sometimes be confused with brown spot or bacterial pustule, which often occur in the same fields and even the same plant, and symptoms can be difficult to separate. The bacteria that cause bacterial blight overwinter in crop residue and on seed, making it favored by continuous soybean cropping, no-till production systems, or fields planted with infected seed lots.

Management

To manage bacterial blight, it is important to differentiate it from brown spot, which can be managed with fungicides. Fungicides are not effective against bacterial diseases such as bacterial blight and bacterial pustule. If bacterial blight was severe in a season, several agronomic practices can help reduce the disease the following year. These practices include:

• rotating to any crop other than Lima beans or snap beans,
• using tillage where soil erosion is not a concern to bury residue or place it in closer contact with the soil for faster decomposition,
• planting pathogen-free seed, and
• selecting resistant varieties.

Although companies typically do not rate varieties for bacterial blight resistance, if a variety is observed to be highly susceptible, it should be removed from the grower's line up.

Reference:

Ampong-Nyarko, K., Offei, S. K., Tetteh, F. M., Yeboah, M., Adu-Dapaah, H., & Akromah, R. (2015). Incidence, severity and yield loss of bacterial leaf blight of soybean in two major soybean growing regions in Ghana. African Journal of Agricultural Research, 10(16), 1865-1872.