I'm extremely new to gardening and I suspect my spearmint plant is suffering from both insects and fungus. I've checked other spearmint questions on the site, but I'm too inexperienced to tell if I have the same problems. Here's what I've got:

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I have 2 spearmint plants, both less than 8" tall. I noticed this problem about three or four days ago (but it could have appeared earlier). The leaves look chewed with a dark outline around damaged areas. Leaves are also yellowing and some are covered with a substance that looks like hard water buildup (but isn't, obviously). As you can tell from the first picture, the entire plants haven't deteriorated too much, but I'd like to get this cleared out before it gets worse. I've read that spearmint is hardy, but mine seems to grow slowly.

There is a crape myrtle nearby that has yearly fungus problems, so I suspect it's picked up that fungus (don't know what it is). I've also seen a substance on the leaves that looks like what I can only describe as a thick buildup of dust (could be webbing, maybe), as well as black specks that could either be small dead insects or droppings. I haven't been able to find any insects on the plant itself. There is nothing unusual on the underside of the leaves.

I purchased a spray bottle of ready-to-use Neem oil for some other plants. Would it help here? Any advice would be greatly appreciated!