Introduction:
Oedema (edema) or intumescences are lesions that can occur on begonia, ivy geraniums, cactus, cleome, ivy, ornamental sweet potato vine, and annual thunbergia. Broccoli, cabbage, cauliflower, and tomato can also suffer from this disorder. Houseplants with fleshy leaves, such as jade, peperomia and schefflera, may be prone to edema when the environmental conditions are favorable.
The lesions have been called a variety of names, including intumescences, galls enations, oedema, edema, and oedemata. Two of the more common names are oedema and intumescences.
The target audience of this factsheet is commercial greenhouse growers.
Symptoms vary and depend upon the plant species, and tenderness of the plant tissue. These symptoms may be confused with an infectious disease or insect gall.
Recent research has shown differences between oedema (primarily occurring on ivy geraniums) and intumescences occurring on tomatoes and ornamental sweet potato vine (Ipomoea sp.).
Oedema:
Bumps, blisters, or water-soaked swellings form on the underside of leaves. These blisters are at first small 9about one to two 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 can be affected.
Ivy geraniums with only mild symptoms of oedema often recover. However, some plants may be severely infected, with significant leaf drop and distorted growth, that they will not be saleable.
Oedema on ivy geraniums may be confused with two-spotted spider mite feeding damage or thrips-feeding damage. As spider mites feed, the plants develop ‘oedema-like’ symptoms that often spread to the youngest leaves. Stippling or flecking from spider mite feeding does not occur on ivy geraniums. To distinguish two-spotted spider mite feeding injury from oedema, use a 10x to 20x hand lens. Look on the underside of leaves for the two-spotted spider mites.
Oedema may also be confused with thrips-feeding injury. Using a hand lens, look for the small, yellow thrips larvae, on the underside of the leaves. As thrips feed on ivy geranium leaves, white scarring and leaf distortion may be noticeable, especially on the youngest leaves.
Favorable Conditions:
Oedema is thought to be caused by an imbalance of the plant’s water uptake and water loss. It develops when the plant 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.
In the greenhouse, susceptible varieties of ivy geraniums often develop oedema in the late winter or early spring, when the air is most humid with poor air circulation that reduces the plant’s transpiration rate.
Researchers at Kansas State University found that high growing medium water contents did not increase the incidence of oedema on four cultivars of ivy geraniums but increased overall plant growth. Feeding plants with supplemental calcium also had no effect on oedema on ivy geraniums. Selecting less susceptible varieties is probably the best way to manage oedema on ivy geraniums.
Intumescences:
The physiological disorder known as ‘intumescences’ is characterized by individual epidermal cells swelling on the surface of leaves. There are small bumps or protrusions on the surface of leaves and petioles on ornamental sweet potato vine, cuphea and tomatoes. Cultivars vary in their response to this disorder.
On certain cultivars of Ipomoea (sweet potato vine), white, crusty eruptions resembe grains of salt, and develop along the leaf veins. Intumescences do not develop on these crops when grown outdoors; only in the greenhouse. Greenhouse coverings have a UVB block inhibitor to extend their life. When plants were grown under supplemental UVB radiation, there was reduced incidence of the intumescences.
Growers should avoid growing the very susceptible cultivars such as ‘Blackie’, ‘Black Heart’, ‘Desana Bronze’, ‘South of the Border Chipotle’, ‘Sweet Caroline Bronze’, ‘Sweet Caroline Sweetheart Red’ and ‘Tricolor’.
By Leanne Pundt, UConn Extension, 2011, latest revision May 2024. Reviewed by Dr. Y. Li, CAES.