Plant pathologists consider a vegetable to be sick (diseased) when it doesn’t develop or produce normally because it is being attacked by some living organism.
A typical leaf or stem infection has the following appearance: a sunken, brown center is bordered by a tan or yellow area that is surrounded by a pale green border into which the disease is growing. Infected fruit also shows similar color zones. Although leaf and fruit discoloration may occur with insect damage, the discoloration does not appear in definite zones.
Bacteria are typically one-celled plants that swim through every inch of your soil. By estimate, 1 pound of garden soil contains over 2 million bacteria. Fortunately, most bacteria are harmless, and many are beneficial in helping to break down organic matter in the soil. Some, however, kill vegetables or make them inedible. The most visible characteristic of bacterial infections in vegetables is an oozing, gelatinous fluid flowing from the infected area.
You might find any of the following three kinds of bacterial damage in your garden: bacterial spots, soft rots and wilts.
Bacterial spots, or blight, may start as dark green spots or streaks on the leaves and stems, then later turn gray, brown, or reddish-brown, and ooze a gelatinous fluid. The spots may even drop out, leaving ragged holes, and the leaves may wither and die. Scabby or sunken brown spots or blotches caused by bacteria are generally called blights.
Bacterial Spots. Courtesy Missouri Botanical Garden plant information.
Prevention and control: Rotate crops; keep plants vigorous by fertilizing.
Chemical control: Fixed copper sprays help control rot and blight.
Soft bacterial rot may infect the leaves, branches and fruits of plants. The infected area is generally bordered by a lighter yellow or tan area. Advanced infection causes large sunken dark areas on the fruit that frequently ooze a gelatinous fluid.
Soft Bacterial Rot. Courtesy Missouri Botanical Garden plant information.
Prevention and control: Avoid planting in undrained soil; rotate crops on long rotation.
Chemical control: Treat soil with diazinon before planting to control insects that spread rot.
Bacterial wilt occurs when the bacteria invade and plug up the water-conducting tubes of the plant. If you slice the stem of an infected plant, it will ooze a gelatinous fluid. To the gardener’s dismay, often seemingly healthy, vigorous plants simply dry up and wilt overnight.
Bacterial Wilt. Courtesy Missouri Botanical Garden plant information.
Prevention and control: Destroy infected plant; grow resistant varieties.
Chemical control: Use organic chemicals to destroy insects that spread bacterial wilt. Certain insects such as the flea beetle and cucumber beetle carry bacterial disease in their digestive tracts. When these beetles have lunch in your garden, they spread the disease.
The next blog will cover viruses, parastic nematodes, plus Vegetable Diseases at a Glance.
© Copyright by Karen Newcomb
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