Legumes such as Phaseolus vulgaris are affected by various fungal diseases that are widespread in tropical to semi-tropical growing regions around the world.
Figures 1a and 1b - Alternaria Leaf and Pod Spot, Alternaria spp. Lesions appear as small circular to irregular spots and flecks with a pale brown center and a dark margin on leaves and pods. Lesions may enlarge (5-15 mm in diam.) as concentric rings.
Figure 2 - Cercospora Leaf Spot and Blotch, Cercospora spp. Brown or rust-colored lesions (2-10 mm in diam.) may vary in shape (circular to angular) with a gray center and slightly reddish border. Tissue in in the lesions dries and falls out. Lesions can occur on other plant parts.
Figure 3 - Floury Leaf Spot, Mycovellosiella phaseoli. Light green to slightly chlorotic lesions (10-15 mm in diam.) form on the upper leaf surface with white floury mats of fungal growth on the lower surface of leaves (rarely on the upper surface).
Figure 4 - Gray Leaf Spot, Cercospora vanderysti. Light green to slightly chlorotic lesions (2-5 mm in diam.) are usually delimited by veins and veinlets on the upper leaf surface with grayish white fungal growth on the lower surface of leaves.
Figure 5 - Powdery Mildew, Erysiphe polygoni. Slightly darkenedspots (10 mm in diam) become covered by growth of white, superficial, powdery mycelium on leaves. infection can occur on stems and pods as well.
Figure 6 - White Leaf Spot, Pseudocercosporella albida. Lesions appear as white, angular spots (2-5 mm in diam.) restricted by veins.Spots become slightly gray with age and may appear pale green to yellow (chlorotic) on the upper leaf surface.
- Presence of previously infested crop debris
- Lack of crop rotation
- Poor sanitation of previous legume debris
- Contaminated seed
- Susceptible varieties
- Moderate to high moisture conditions
- Infection at V4 – R2 enhances symptom severity, reduced pod set, poor seed fill, and yield loss
Courtesy of H. F. Schwartz & S. K. Mohan (09/2011)