If the pests were leafminers, it should be helpful to know that total leaf loss from such damage rarely affects the tree’s general health.

That said, identifying a pest without images or samples is extremely difficult. The common insects, which could be described as “small worms” and which damage elm leaves here in the northwest, are three: Elm leaf beetles (Xanthogaleruca (=Pyrrhalta) luteola) remove the surface of leaves, the total ranging from minor to nearly complete; elm leafminers (Fenusa ulmi) damage the leaves but are inside the leaf, between the upper and lower surfaces, with damage also ranging from minor to extensive; and spiny elm caterpillars (Nymphalis antiopa), which feed in groups and can remove large quantities of leaves.

Then, too, we should add fall webworms (Hyphantria cunea) to the list if they were groups of inch-long caterpillars which encased portions of branches in obvious webbing.

Of all those, management is physical, destroying the insects. Chemical management is recommended for only one: the elm leaf beetle. If the pests are elm leaf beetles, it’s now too late in their life cycle for any action.

You said that you “still see evidence of the little worms in some of the remaining trees.” It could be helpful to send me at least 2 images – one an overall view, with another one or two well-focused close-ups. If you are unable to take and send images, it’s very likely a friend, neighbor, or relative can help.

If the pests and their evidence are gone, we will need to wait until next year. Then, at the very first sign of damage, please send images as suggested above.

RE: query from last year about Camperdown Elm tree.

Sorry, for some reason my text didn't show up with the picture. This is what about 5% of my leaves look like right now, as the pest has returned. More leaves are succumbing by the day. What can I do now to prevent this from occurring next year? The worms/pests are definitely between the two layers of leaves. Thank you!

What a nice surprise. Few people followup with a new message.

Thank you for sending the new image. It reveals that the pests are leafminers (Fenusa ulmi) which feed between the upper and lower layers of the leaves. The only impact is esthetic -- the affected leaves look ugly for a time! Unfortunately, Camperdown elms will retain those blotchy affected leaves for the season.

Because my schedule is very tight today, I would like to delay a complete response until tomorrow.

Thank you. I also just realized today that I see the same kind of pest on our very tall and old elm trees. We have two elms (I think American elms?) located about 20' and 30' away from our Camperdown elm. It appears the exact same kind of pest is getting to those leaves as well. So I guess I need to figure out what to do about that as well.

Yes, it's likely to be the same pest, but with 2 differences. On American elms, the damage makes large splotches, rather than limiting the damage to between the veins.

The second difference is that American elms may drop the damaged leaves and, if not, will overgrow and hide the ugliness.

Just as with Camperdown elms, the damage is not significant to the tree's health. So, the good news is that none of your trees need treatment.

But, if you prefer to have them sprayed, be aware that the application must be made shortly after the adults arrive. (It's too late now.) Consult at least 3 Certified Arborists for how they might handle the issue next year, then make arrangements with the company you feel most comfortable with. You can locate nearby Certified Arborists using your zipcode at http://www.treesaregood.org/.

See "Selecting a Pest Control Company" at http://npic.orst.edu/pest/selectpco.html.