A Keen Eye Can Help You Spot Edema On Your Vegetables
Vegetables very susceptible to edema include tomato (foliage and fruit), beans (foliage and pods), cabbage, broccoli, cauliflower, Brussels sprouts, potato foliage, and most cucurbits (fruit, foliage, and stem).
Edema (aka, oedema or corky scab) is a common, noninfectious disease of many vegetables. Edema may be mistaken for an infectious disease or insect gall. Edema is a physiological condition caused when plants take up water faster than it can be used and transpired. Edema spots generally do little damage to plants, but can detract from the appearance of vegetables and may render them unmarketable causing economic loss.
It is likely that all succulent tissues of vegetable crops are susceptible to edema under the proper conditions. Edema is most often seen in cabbage growing in waterlogged soil and in tomatoes during wet weather.
Indicators of edema are variable and depend on the plant species, the plant parts affected, and tenderness of the tissue. Initially, symptoms appear on the succulent leaves, stems, flowers, and fruit of susceptible plants as single, minute, water-soaked blisters, warts, or galls.
Symptoms are especially common on undersurfaces of leaves and occasionally will form on the larger veins and petioles. The single, pimple-like blisters usually are about 1 millimeter (mm) to 2 mm in diameter, but frequently two or more spots will merge to form a line of spots or a large affected area forms. Following rupture of the blisters, the exposed surface may become rust-colored, brown, or tan, with corky texture. Severely affected leaves of certain plants may become cup-shaped or turn yellow and drop prematurely.
Excess soil moisture combined with warm soils, cool air temperatures, overcast weather, and poor air circulation can cause a buildup of water pressure within the leaves. Under these conditions, roots absorb water at a rate faster than is lost through transpiration.
Edema stops developing when the weather conditions change, but existing spots remain on the leaves resulting in cosmetic damage.
Changes in weather and cultural practices of growing plants usually will avoid edema. Growers can reduce the risk of edema occurrence by adopting the following practices:
- Avoid irrigation or watering during cool, overcast humid weather. Irrigate when air temperatures are rising or humidity is low.
- Prevent edema by allowing the top two inches of soil to dry between watering and space plants to allow for sufficient air circulation.
- In greenhouses: a) reduce the humidity of the air by venting; b) improve air circulation; c) increase light intensity; d) space the plants farther apart; e) use a well-drained
- Avoid over-fertilizing, especially when the plants are growing slowly, such as during the late fall and winter. Maintain fertility based on a soil test. Avoid low levels of potassium and calcium.
- Varietal selection: Some cultivars might be more susceptible to edema than others.