Diseases in garden vegetables are pathological conditions caused by bacteria, fungi or viruses. Fungal diseases are the most common garden vegetable diseases, followed by viruses, then bacterial infections. Treatment for disease ranges from applying fungicide to removing and destroying plants that are affected. Many bacteria and viruses survive within the ground from season to season.
Bacterial infections cause diseases such as bacterial canker and bacterial spot and speck, which affect tomatoes, according to the University of Connecticut.
Potatoes are affected by common potato scab, which causes raised, scabby patches; ring rot, when the potato rots from the inside out; potato late blight, in which dark and sunken patches develop on the skin; and bacterial rotting, when the tuber is attacked by a bacteria that causes the potato to rot.
Carrots are affected by carrot leaf blight, which causes black spots to form on the leaves, and bacterial blight, which causes small spots with yellow edges to form on the leaves.
Bacterial leaf spot affects basil, peppers, sugar beets, pumpkins, cucumbers, squash, muskmelon and watermelon. Common blight and halo blight affect beans such as lima, pole, snap and Southern pea.
Cucumbers, squash, watermelon, zucchini, scarlet runner beans, lima beans, snap beans and carrots are affected by mosaic virus. This virus causes the leaves of the plants to distort and discolor in a mottled pattern, according to the Ohio State University Extension.
Lettuce and other leafy vegetables are susceptible to lettuce mosaic virus, lettuce big vein agent, aster yellows mycoplasma, beet western yellows virus, broadbean wilt virus and Biden's mottle virus.
Peanuts are affected by rosette virus.
Potatoes are affected by potato leafroll virus and potato virus X, as are tomatoes; potato virus Y, which also affects peppers; potato virus S and potato virus A. In addition to being affected by potato viruses, tomatoes are affected by tomato spotted wilt virus.
Fungus causes a variety of diseases. Verticillium wilt affects eggplant, peppers, potatoes and tomatoes, according to the University of Illinois Extension. Anthracnose, which causes dark spots to form on leaves, affects watermelon, muskmelon, asparagus, beans, eggplant, peas and sweet peas. Fusarium wilt affects sweet peas and beans. Southern blight affects beans, sweet potatoes and tomatoes. Foot and root rots affect tomatoes, cucumbers, peas and beans. Powdery mildew affects Brussels sprouts, amaranth, melons, cucumbers, okra, hyacinth beans, rutabagas and turnips. Fungal leaf spot affects Swiss chard, peanuts, lima beans, celery and beets. Damping-off disease affects peas. Crown rot affects asparagus.