Question: What causes my Chinese elm’s leaves to look like lace by mid-summer? The tree is entirely brown when it happens.
Answer: That’s the damage of the larvae of elm leaf beetles. If you look closely, you’ll see small green worms with brown stripes running front-to-back. Control them with any general-purpose insecticide applied with a power sprayer as soon as you see the damage. You may have to spray two or three times during the season. For the record, you probably have “Siberian” elms (Ulmus pumila), not the true “Chinese” elms (U. parvifolia), which are much better trees.