The Walden Effect: Farming, simple living, permaculture, and invention.

Sweet potato oedema

Oedema on a sweet potato leaf.When I see a problem with one of my plants, my first thought is, "Okay, is this caused by a bacterium, fungus, or insect?"  It took me half an hour on Monday to realize that the white specks on the upper leaves of my sweet potato slips were none of the above.

The Cornell University Plant Disease Diagnostic Clinic resolved my mystery:

Oedema occurs when roots take up water faster than it can be used by the plant or transpired through the leaves. Water pressure then builds up in the mesophyll or internal cells of the leaf causing them to enlarge and form tiny swollen blister­like areas....

Oedema is most prevalent in the late winter especially during extended periods of cool, cloudy weather. It is likely to develop when the soil is warm and moist and the air is cool and moist. This environment results in rapid water absorption from the soil and slow water loss from the leaves.

I turned off the grow light when I moved all of the other plants outside to harden off, which (along with a week of rain and high humidity) slowed transpiration of water out of my sweet potato slips.  I've turned the grow light back on to help the slips transpire until the sunny weather returns.

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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.

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