I never have seen anything like that, but it doesn't look too scarey.

I'd wash it off with a strong stream of water from the garden hose (like you do with aphids).

If that didn't get rid of it, I'd spray it with a solution of dish detergent in water & follow with a clear water rinse .

If that doesn't work, or if it does but the problem recurs, then I'd take a leaf in to the County Agricultural Extension agent for help.

Best luck.

sylvia

ps: How do you have green leaves in Michigan when all I've got in Texas is anticipation???