Looks bacterial from here, but I don't live in an area that can grow these plants...

Dan

Not bacterial. Not fungus either.

Instead, leafminers.

They're inside the leaves making the serpentine trails, so spraying won't help.

I really oughta send these to the better half, who worked the Extension counter, albeit in the west. So jean the serpentine trails are an indicator, but these miners cross the veins and cause that marginal leaf cell decomposition and necrosis?

Dan

Yeah, Dan if you have any more info I would appreciate it.

I have removed as much of the affected foliage as I could.

Now, from what I know about miners, after they complete their life cycle in the summer, they are done for the year; is that correct? If so, that would help explain why the trees always start looking better later in the summer. These have been planted for 3 years, and it's been the same thing every year. The 2 trees sit 20 feet from one another, but the vast majority of the problem is on one, the other has very little.

Now I have been reading this morning of some systemic insecticides that can be absorbed by the leaves and possibly kill miners. What are some product names of a systemic insecticide that might be available retail?

Leaf miners can be addressed with other than systemic insecticides, but your timing has to be spot on if you want to use sprays. They don't spend their entire life-cycle inside the leaf. And you will have to spray in that interval when they are external to the plant.

I used to raise bearded iris for sale, and that meant the State inspector had to monitor my mother stock. I had a beginning infestation of iris borer on one variety, and she explained to me how they enter the leaves and then migrate into the rhizome and how to monitor for the earliest signs of them before they damaged the root stock. Same way with leaf miners.

Due to your zone, I don't know if what you have are magnolia leaf miners or not, but they do produce damage like leaf scorch, in addition to the mines. Leaf miners can be moths, weevils, etc. it's a generic name for any insect who does this type of damage. So you have to identify the causative pest. Magnolia leaf miners do lay their eggs inside the leaf, the insect pupates in there after their larval stage, and emerges to the outside in summer.

I just wanted to post an update. I finally found some Bayer tree and shrub systemic insect and pest killer. It was kind of hard to find, none of the box stores carried anything like that but I finally found some at a local farm store. It's for ground application around the root zone, so I applied it a couple days ago. The application instructions said nothing about applying to the foliage, but I'm curious if I could have done that for quicker circulation into the leaves. Now I'm not going to do that since I've already applied to the root zone, I'm just curious. I have removed as much affected foliage as I could find, now I'm just curious as to whether it's too late for the insecticide to do any good this year or not. If it is, at least now I know to treat early in the spring next year.

I'm going to keep posting to this thread, hoping someone with experience battling leaf miners will see it. After some research, I think it's the yellow poplar weevil, although I have yet to see a single bug. I've treated the ground with a systemic insecticide, however I'm wondering if anyone has ever had any luck treating this late in the season. The tree is very unsightly and it's a focal point next to the driveway.
So this is the second year I've battled these, last year I just didn't know what it was. The tree has only been planted 2 years also. I hate taking out trees, but I hate even more having a tree that needs constant pampering. Anybody ever have any problem with sweetbay magnolia leaf miners? Most everything I've read says it's not very common to have pest problems with sweetbay, so I'm wondering why my trees?

Because you've had the problem in 2 successive years, it's likely to continue. May well be a common problem with such trees in your region. (You should ask at a local large independent garden center.)

That said, because you only have 2 years invested in the tree, consider replacing it this fall with a less troublesome kind of tree, one that looks good in your focal point.

The problem is this: The longer you keep it, the more reluctant you will be to start over.

jm30 - thanks for the posts and updates - keep 'em comin'! I just found the same white 'stuff' and trails on 2 of my sweet bays yesterday. Have had them for 3-4 yrs and have never seen this but they have always been an issue as far as slow growth, very few leaves, and it looked to me like there was a fungus or something on the trunk. I've asked the nursery about it and when they see new growth they just tell me to "give it time". I'm tired of waiting for these trees to do nothing! I'll do some research and see what I can find.

I am beginning to see some improvement. I have given it 2 treatments of neem oil to the foliage, making sure to thoroughly get the new growth. I am seeing less and less on the new foliage, which is the ones the miners go for because of their softness. Of course there is no reversing the damage on the existing leaves. Now I can't say for sure that it's the neem oil helping, or if the pest is finishing it's life cycle for the year. I know some miners finish their life cycle by mid summer.
I would consider removing the tree, but the fact that there is another sweetbay only 20 feet away that has hardly any infected leaves, makes me think I can eventually be successful. I did forget to mention that this tree did suffer some damage in an ice storm last winter, quite a few broken limbs that had to be pruned off. So it started the spring a little stressed.
Jill-I've never seen anything on the trunks, they always look healthy. It's just the leaves.

GOOGLE "Verticillium wilt" see if this helps.