Black Stems & Wilted Leaves on Pole Beans

Identification

• Pole beans are susceptible to charcoal rot or ashy stem blight caused by Macrophomina phaseolina. The soil-borne fungus infects plants during all stages of growth. Plants growing under stress of drought in very hot temperatures are more prone to the disorder.

Damage

• Initial symptoms of disease include the appearance of sunken black areas or cankers on plant stems. The cankers often display concentric rings and sharp edges. Stems start to break at the canker location. Foliage starts to yellow and wilt, followed with premature leaf drop. Black, charcoal-like dust often appears on older plants. Plant growth is stunted. Younger plants die.

Management

• Rotating crops helps to reduce the chances of infection. The University of California Extension recommends a three-year rotation with any cereal crop to reduce inoculum. Keep plants well irrigated to minimize drought stress.