Tuesday, November 27, 2007

Greenhouse - Edema or Water Blisters

Edema on Ivyleaf Geranium
Photo from Iowa State University Horticulture Home and Pest News.

Edema or water blistering is a common problem in some greenhouse grown plants such as ivyleaf geranium. The following is a short article on the subject.

During periods of cloudy weather, greenhouses are apt to be cool and humid. These environmental conditions favor the development of edema (oedema). When the growing media remains moist and the plant roots absorb water at a faster rate than is transpired through leaf cells, the leaf cells rupture. This rupturing of the leaf epidermis and the inner cells causes the raised, crusty appearance on the underside of the leaf.

Edema is commonly found on ivy geraniums and cultivars vary in their susceptibility. Experienced growers will select varieties less susceptible to the problem. Other greenhouse crops susceptible to edema include: sweet potato vine (ipomea), begonias, cacti, ferns, palms, pansy, cleome and cole crop vegetables like broccoli, cabbage and cauliflower.

Symptoms of edema appear as bumps or blisters initially on the undersides of lower or older leaves on a plant. They may then turn brownish or tan and become corky. Severely affected leaves will turn yellow and fall off the plant.

To reduce the incidence of edema: Use a well drained growing media, avoid over watering, and keep plants on the "dry side" during extended periods of low light and cool temperature. Plants grown in saucerless hangers with reservoirs of water inside the pot are more prone. Ventilate whenever possible to lower humidity and use horizontal air flow (HAF) fans to hasten air movement and maximize plant transpiration. Increase light intensity. Space plants farther apart. Avoid over-fertilizing plants, and avoid cultivars that are highly susceptible to edema in your greenhouse.

Article from the University of Massachusetts Floriculture Timely Topics, 3/2/04.

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