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I've read that white patches on zucchini can be natural, powdery mildew, or another fungus. How do I know which?

2 of my zuchinni have large patterns of white areas on all leaves older than about a week. New growth seems to be coming in without any white. What can I use to identify the cause?

Overall the plant still seems reasonably healthy, but is that a reason not to worry?

The soil is alkaline but fairly rich with a fairly large amount of compost ammendment at the beginning of the season.

My goal is not 9nly to identify the potential issue, but to know how to identify it myself in the future, so if you ar eable I would appreciate more than "that like like X to me."

whole leaf

close up of leaf

Matt Flamm
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The mildew that affects many squash plants grows on the surface, and can be scraped off. The white patches you show, which are exhibited by many squash varieties, are internal to the leaf tissue.

kreemoweet
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The above commenter is correct: Your squash is normal, that's just how some of the leaves are.

As for how to tell for yourself, over time you'll get used to patterns and what's normal and what's not. Different varieties will have different patterns.

If you look carefully, you'll see that the white is integrated with the leaf--it stays within the boundary of the veins and if you look at it from the side, it's not sticking out of the leaf surface. (A few little spiky hairs are normal.)

I've attached a picture of a completely green squash leaf with mildew (sorry for the poor quality). Even without a side view, you'll notice that the white part is patchy and above the leaf surface. It just doesn't look right...and that's usually a sign something awry.

enter image description here

Often there will be other symptoms like a bit if yellowing under the bigger patches, but the best indicator is that it's not something within the leaf itself but separate from it.

If you ever get leaf miners, as happens to me in late summer, you'll see it's under the leaf, but doesn't stay within the boundaries and definitely looks off.

Happy growing, hope you harvested more squash than you can eat!

Josh
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