Why are my hydrangea leaves curling up?

Chicago Tribune

25-05-2025

I checked with the Chicago Botanic Garden's Plant Health Care supervisor, who has seen this same problem in some of the Garden's hydrangeas this spring. Your description fits the damage we see from the hydrangea leaf-tier moth () that attacks several hydrangea species but prefers Annabelle and Incrediball® hydrangeas. Hydrangea leaf-tiers are small moths that are active now and whose larvae sew leaves at the end of stems together with a silk thread. Once protected inside the enclosed leaf, they feed on the leaves and flower heads. These leaf enclosures become puckered and are easy to notice. They are generally located toward the top of the plant. By pulling apart the leaves, you can find the slender green caterpillar that is up to ½-inch long with a blackish head, which will verify the problem.
This insect emerges from the soil in spring as a small, brown and white moth that you might not notice in your garden. The moths lay eggs on the branch tips of hydrangeas and the hatching caterpillars cause the damage you see in your garden. The larvae drop to the ground to pupate in summer and emerge as adults the following spring.
I do not usually try to control this insect, as the damage is minor and mostly cosmetic, even though the damage can be obvious when populations are high. You can carefully open the leaf pouches and smash the caterpillars inside and/or remove and destroy any leaf masses that you find. Try very carefully squishing the caterpillars without opening the pouches to save some time. Treating with an organic product that contains Bacillus thuringiensis kurstaki is another option, but you must apply it so that the product gets inside the cupped leaves. As a last resort, consider using a pyrethroid insecticide to kill the caterpillars, but that needs to be applied directly on the caterpillars for it to work properly. Bottom line, this is not much to worry about.