Diseases That Affect the Phaseolus Vulgaris

Bacterial Infections

• Bacterial brown spot spreads through contact with infected plants, causing brown leaf spots and holes with a burnt appearance that are typically one-eighth to three-eighths of an inch in diameter. Bacterial wilt is spread through contact with the infected seeds or foliage of another plant, can also spread by irrigation water and is more likely to strike plants that have open wounds. Bacterial wilt causes the entire plant to wilt and turn straw brown before dying.

Bacterial Blights

• Halo blight is spread by water and contact with infected plant matter left on the ground over the winter. The first indication of halo blight on a bean plant is a series of squared spots with a damp appearance. Over time, these spots increase in size and develop yellow rings. The early signs of an infection are spots with a damp appearance that eventually enlarge into limp brown areas with a bright yellow fringe. Extensive infections can cause leaves to drop and the entire plant can wilt if the infection spreads into its stems.

Foliar Fungi

• Fungi that attack the leaves and seeds of bean plants are commonly spread through contact with infected plant materials or tools. Fungi also release spores, with splashing water, wind and insects commonly spreading fungi between plants. Powdery mildew, rusts, white molds and alternaria, ascochyta or angular leaf spot attack bean plants. These diseases are characterized by round spots of fluffy material on the seeds and leaves of the plant with a dark or white coloration. Anthracnose is characterized by large discolored sunken areas of foliage. In damp conditions, masses of spores can form on these lesions.

Root Rot

• Fusarium, pythium and rhizoctonia root rot attack the root systems of phaseolus vulgaris. The first symptoms of these diseases occur in the root system, where they are easily detected by shrived roots that are colored red or covered with lesions. The first sign of root rot in the above-ground portion of the plant is wilting, followed by the plant's rapid death. Damage from root rots are more severe during cold weather when the soil is consistently wet or your beans are already weakened from another disease.

Parasites

• Root-knot nematodes live in the soil. These parasites penetrate the roots of the plant and cause it to form swollen areas called galls that can reach up to one-half inch in diameter. These galls restrict the growth of the plant's roots and can cause yellowed foliage, wilting, stunted growth and burnt looking areas around the edges of leaves. Spread through the movement of infected soil, they are most common in fast-draining sandy soils that have an average soil temperature between 77 and 86 degrees Fahrenheit.

Viruses

• Curly top virus results in severely diminished growth and puckered leaves that curl downwards into tight bundles. It is spread during warm weather in the winter and spring through contact with infected plants or insects such as the beet leafhopper. Mosaic viruses damage bean plant foliage, resulting in deformed or stunted growth and reduced bean production. Bean plants infected with the common mosaic virus have mottled leaves with irregularly shaped light yellow and dark green spots. Golden mosaic virus causes a mottling of large bright yellow spots, while yellow mosaic virus causes spotted yellow leaves and stunted growth. Mosaic viruses are commonly spread by aphids or whiteflies.