Brown Spots on Lilac...Burned?

[missM]

I just noticed these brown spots on the leaves of my lilac. Did it get burned? Any way to prevent? Is my lilac going to make it?

[rainbowgardener]

Let's see.... No. Yes. Yes.

No, it didn't get burned. It looks diseased, but fortunately for you, I don't think it is. I think what you have is lilac leaf miners.

The lilac leaf miner is a small, brown moth that lays eggs between the layers of the leaves. The eggs hatch out into little caterpillars, which chew their way around the leaves and cause the damage. It is interesting, because leaf miners in other plants usually leave little pale squiggly tunnels behind them:

Here they are in close up:


https://ketenewplymouth.peoplesnetworknz ... damage.JPG

But for some reason, the lilac reacts differently and you get those ugly brown blotches.

The good news is that it is mainly a cosmetic problem. The leaf miners don't damage the tree and the lilac can lose that much leaf surface without missing it much. It is going to lose those leaves in the fall anyway.

It is difficult to do much about now. You can remove the blotched leaves. If you get them soon enough, that helps prevent the next generation. When the caterpillars have eaten/ grown enough, they chew out of the leaf and drop down to the soil, burrow in a bit and pupate. Then they emerge as the adult moth and start the cycle over. So if you remove the leaf while the caterpillar is still in it you prevent that. You can also help prevent it by mulching well around the tree - makes it harder for the caterpillar to get to the soil to pupate.

But the caterpillars are very protected inside the leaf and nothing much you can spray on the outside will do anything to them.

Prevention is to spray NEEM oil early on (late April-early May), which repels the moth and keeps her from laying the eggs in the leaves. Do it again in July to protect from the next generation (since the moths fly, ones that hatched out in other people's yards can come lay eggs in your tree).

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[missM]

Wow! Thank you so much for the super detailed response!

I'm glad it's primarily cosmetic.

Should I still spray with NEEM oil this July? Also, is NEEM oil better than hot pepper wax? I've been using hot pepper wax around the garden and it works on most of my plants, but not so well with others.

I really hope I can get this under control.

[rainbowgardener]

I wasn't familiar with the hot pepper wax. Lots of people do DIY garlic-pepper sprays, with a bit of salad oil mixed in to help it stick. But the wax seems like it sticks better. The homemade garlic pepper sprays usually have to be re-applied after rain.

Seems like it should work. Repellent qualities and a barrier to help keep the moth lady from being able to lay her eggs inside the leaf.

So yeah spraying it with that in a couple weeks may help prevent the next generation of them.

But don't stress too much, like I said it is only a cosmetic problem. My big old lilac doesn't get these, but every year by mid summer-ish, it gets powdery mildew, which is a fungal disease. It also messes up the leaves and also is only a cosmetic problem for the lilac, so I don't worry about it too much.