Edema
Edema .jpg) Susceptible Plants- Edema (oedema) is a common physiological disorder affecting a number of greenhouse crops including begonia, ivy geraniums, cactus, cleome, ivy, ipomoea and annual thunbergia. Broccoli, cabbage, cauliflower and tomato (leaves or fruit) can also suffer from this disorder. Houseplants with fleshy leaves such a jade, peperomia and schefflera may be prone to edema during favorable environmental conditions. Edema also occurs on woody plants such as camellia, hibiscus, and yew when soil is waterlogged and transpiration is impaired Symptoms- Symptoms of edema vary depending upon the plant species or cultivar affected. Bumps, blisters or water-soaked swellings form on the underside of leaves. These blisters are at first small, about 1/16 in.(1 to 2) mm in diameter. They then turn tan or brown and become corky. Severely affected leaves turn yellow and drop from the plant. Sometimes, stems and petioles become infected. On certain cultivars of Ipomoea (sweet potato vine) white, crusty eruptions resembling grains of salt, develop along the leaf veins. Growers may confuse these symptoms with an infectious disease.
On susceptible cultivars of Cleome, tan eruptions form on the upper leaves, leaf petioles and stems. Affected leaves curl and become distorted. This disorder is also referred to as intumescence. High light, high humidity and poor air circulation is reported to encourage intumescence On susceptible cultivars of thunbergia, small, tan eruptions, resembling small insect galls, form on the underside of leaves. A yellow spot may be seen on the upper surface of the leaf.
Causes- Edema is thought to be caused by an imbalance of the plant’s water uptake and water loss. It develops when the plants roots absorb water at a faster rate than it is transpired through the leaf cells. The enlarged leaf cells divide, and then rupture. This rupturing of the leaf epidermis and inner cells causes the raised blisters commonly seen on the underside of leaves.
Prevention and Control- Growers can try to prevent edema by changing some of their cultural practices. Select a growing medium that drains well. Space plants further apart so they receive more light. Keep plants on the dry side during cool, cloudy growing conditions. Water when air temperature is rising and humidity is low. Do not water susceptible varieties or crops on cloudy days. Do not remove infected plant parts as this makes the condition worse. Edema is not infectious.
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