Yesterday I noticed that my young water oaks have a white-looking residue on the leaves. You can almost rub it off, but not entirely.

Anybody seen this before?

Bump for afternoon crowd

Not sure what that is. It may be a bit of mineral from something dissolved in water that evaporated? Maybe a white mold?

All I know is that that's not a water oak. Water oaks have smooth leaves. My guess is pin oak since the leaves are kinda pointy.
Maybe powdery mildew (#5):
https://apps.extension.umn.edu/garden/diagnose/plant/deciduous/oak/leavesdiscolored.html

Young water oaks will often be pointed like those in the picture. A more typical water oak leaf in background of the picture-the yellowish brown leaf.
Agree with mineral deposits from irrigation water-actually noticed several holly trees with it today. Is the tree relatively new? If so not uncommon for those deposits to be on leaves from nursery.
I wouldn't worry about it. Leaves will be dropping from the tree in the next several weeks to month-provided we ever get a real cold front.

agnerd said:

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All I know is that that's not a water oak.

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lol

They sprouted in the spring of 2019. They're roughly 7' tall now.

I do have an irrigation system running to each tree, but it's a drip system so there's no potential for overspray to be hitting the leaves.

The water from my well is definitely hard water so that makes sense, but I'm surprised to see residue on the leaves like that.