Disease can attack all parts of a plant, including the roots, leaves and stem. The majority of garden diseases are caused by fungi that feed on tissues, both living and dead. While some fungi are useful, in compost piles, for instance, the byproducts of fungi kill cells, which in turn leads to disease. Viruses are another cause of garden diseases. Classified as parasites, viruses multiply in a living host. Bacteria also cause disease and enter plants through wounds and holes. Their cell walls are surrounded by a slimy capsule, which is often the cause of disease, according to "Rodale's Garden Insect, Disease & Weed Identification Guide," by Miranda Smith and Anna Carr. Garden diseases include wilt, anthracnose and mosaic viruses.
Bacterial wilt affects cucumbers, gourds, melons, pumpkin and squash, according to the North Dakota State University Agriculture and University Extension. Striped cucumber beetles spread the disease from plant to plant. The bacteria enters through a wound and blocks the plant's water-conducting tissue, choking off the water supply. Symptoms include green patches on vegetables, followed by wilting leaves, shoots, stems and finally the entire plant. Test for bacterial wilt by cutting a stem and checking for white strands of ooze. There is no cure for bacterial wilt. Prevent the disease by eliminating the cucumber beetle, which can also cause mosaic virus. Spray insecticide or cover the plants with screening.
Anthracnose is caused by fungus. The disease affects cucumbers, gourds, melons, pumpkins, squash, lima beans, peas and peppers. Affected vegetables have dark sunken sores on the stems, leaves and on the vegetables themselves, according to Clemson University Extension. The virus is transmitted through diseased plant debris or on infected seeds when water from excessive rain or irrigation splashes the spores onto the plant. The spores can survive up to two years in the soil. Prevent the disease by not watering plants from above, using uninfected seeds and collecting and destroying all plant debris after the growing season. Fungicides are only effective on certain crops such as pole and snap beans.
Mosaic viruses affect vegetables such as beans, cucumbers, melons, pumpkins, peppers and tomatoes. Symptoms include discoloration of plants, usually yellow-green, and misshapen leaves. Leaves pucker and curl on bean plants, according to the University of Missouri Extension. On members of the cucumber family, plants fail to grow, leaves are streaked yellow and green and the vegetables are pitted and irregular-shaped. The leaves on the affected pepper plant are covered with yellow blotches and are misshapen. In tomatoes, light green blotches will appear on the leaves, which are underdeveloped.
To prevent all types of mosaic virus, remove and destroy affected plants. Buy resistant seeds. Control pests such as aphids, which transmit the disease from plant to plant.