This week’s sample consisted of several detached leaves from a spathe flower plant. Symptoms consisted of chlorotic blotches and some darker flecking on the leaves. One leaf was completely brown but not decayed. The symptoms were not suggestive of a foliar disease, and no fungi were observed on the spots. As a precaution, some leaf pieces were incubated, but nothing grew out.
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| Edema on spathe flower (Photo: Mike Munster) |
Under the microscope, there were small, slightly raised bumps on the leaves. Mike Munster, the diagnostician who worked with the sample, suspected edema. Edema is a common abiotic disorder that occurs on many herbaceous and woody plants. Edema can be a problem on greenhouse crops and on plants grown outdoors. The most obvious symptoms include the formation of tiny blisters, warts, or raised bumps on the undersurface of leaves. With age, these bumps may become reddish brown and can be mistaken for rust pustules.
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| Notice red pustules on underside of leaf (Photo: Mike Munster) |
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| Edema on geranium (Photo: Mike Munster) |
Typically, edema is a problem in cool, wet conditions when the soil water is warmer than the atmosphere. Edema occurs when the roots take up more water than is lost through transpiration, resulting in accumulation of water in intercellular spaces. Excess water accumulates in the leaf causing leaf cells enlarge and block the stomatal openings. These enlarged inner cells cause the epidermis to rupture and become crusty with age.
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| Crusty edema on tomato (Photo: Frank Louws) |
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| Crusty edema on tomato (Photo: PDIC Database) |
For control:
- Avoid irrigating during cool, humid, cloudy weather.
- Reduce humidity in greenhouses by venting and increasing heat, improving air circulation, increasing light intensity, spacing plants further apart.
- Avoid standing water under pots
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| Edema on swiss chard, notice the blackened stomata (Photo: Mike Munster) |
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| Edema on lilac, similar to fungal leaf spots (Photo: Mike Munster) |
