I managed to get some slips started from a store bought (treated) sweet potato in May this year. Took a very long time to get going but eventually got 3 slips started. One of the three has two leaves affected by what looks like a powder, but it is not loose powder. I tried to rub some off of the leaf at left but nothing detached, I only managed to crush the surface of the leaf. The underside of the leaf looks completely normal.
1 Answer
I am not sure, but it could be colleters. There is a story here about colleters on sweet potatoes, the photos look a little bit different though. They think it is because of overheating.
It can also be a fungal infection, but usually you can scrape that off the leaves.
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Thanks for this interesting comment. I don't think it qualifies as an answer to the problem, but I gave you an up vote for the pertinent contribution. I'm beginning to think it may be just dust of some sort which became "glued" to the surface of the leaves. If it was a disease then other leaves would by now have shown repeat infection but they are all clear. Commented Oct 22, 2017 at 12:35
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Yeah it was a long shot, just trying to think along with you! Thanks for the upvote. I hope the powder problem won't be harmful for your crop.– bennCommented Oct 22, 2017 at 13:27