Wednesday, April 20, 2011

Possible Edema on Tomatoes

I am having an unusual issue with some of my tomato plants. I have noticed some small spots showing up on the leaves that look like tiny blisters. After a few days the blisters get more numerous and eventually the leaf gets dry & crunchy and falls off. This problem seems to be specific to certain varieties of my tomatoes, and although they are all growing in close proximity it is not spreading. My first worry was that I had Septoria leaf spot or something similar to that, but when I started googling images of that it didn't look the same. I eventually found my way to some postings about Edema. In short, this is caused when the roots take up more water than the leaves can use, causing blisters on the leaves.

The most common cause of edema is the presence of abundant, warm soil water and a cool, moist atmosphere. Under these conditions the roots absorb water at a rate faster than is lost through transpiration. Excess water accumulates in the leaf, some parenchyma cells enlarge and block the stomatal openings through which water vapor is normally released from the plant; thereby contributing to further water retention in the leaf. If this condition persists, the enlarged cells divide, differentiate a cork cambium, and develop elongate cork cells externally to form a periderm. The rupture of the epidermis by the enlarged inner cells and the periderm account for the raised, crusty appearance of older edema spots."
Plant Pathology Extension of North Carolina State University

So I have tried to cut back on my watering in hopes that things will get better. I also need to increase the amount of airflow around the plants. Now I am trying to find a medium between dry wilted plants and over watering... Wish me luck!

Can you see the small white spots?
The leaves at the tip have been more severely effected
and have started to dry out and curl.
Eventually they will fall off.

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