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Greenhouse Updates: Apr 16, 2015

Intumescence
April 16, 2015

Intumescence is an abiotic disorder which produces small blisters on leaf surfaces. Severe cases can result in defoliation. Certain plants are especially susceptible to intumescence; these include members of the Solanaceae such as Ipomoea, peppers, and tomatoes, and Cuphea in the Lythraceae family. The symptoms resemble and are often mistaken for edema (or oedema), but their development is distinctly different. In addition to the genus of the afflicted plant, the location of the symptoms is also helpful in distinguishing intumescence from edema. Edema is commonly observed on the undersides of leaves, as on ivy geraniums, whereas intumescence usually appears on upper leaf surfaces. Ivy geraniums are susceptible to edema, which is caused by an imbalance in water relations in the plant, and is best avoided by selecting resistant cultivars. Symptoms of intumescence may also be mistaken for galls formed by eriophyid mites; however, mites will be absent, and intumescences may appear in a pattern, whereas mite galls distribution is more random.

Recent research from Kansas State University indicates that intumescence is caused by decreased UVB radiation, a condition that may occur as a result of a long stretch of cloudy weather, or the application of shade cloth or other material that blocks UVB radiation. Symptoms are nearly always seen in greenhouses or growth chambers. Rare cases have occurred outdoors. Recommendations thus far for preventing intumescence are limited to spacing plants to allow full light exposure.  Some cultivars of a species may be more susceptible than others, though little information about this currently exists for plants other than Ipomoea.

Photos of Intumescence:

For more information: Oedema and Intumescences, UMass Extension

Intumescences: A Physiological Disorder of Greenhouse-grown Crops, Greenhouse Product News

Intumescences: Further Investigations into an Elusive Physiological Disorder, Greenhouse Product News

Angela Madeiras, UMass Extension Plant Diagnostic Laboratory