“My Annabelle hydrangeas have some leaves that appear to be rolled up. I am seeing more this year than in past years. Is this something that needs to be treated?”
— Simon Becker, Riverwoods
Advertisement
Your hydrangeas, like those in other gardens around the North Shore, have hydrangea leaftier (Olethreutes ferriferana) present. The damage caused by this insect appears as up to four leaves tied together with silk at the end of a branch or top of the plant.
My hydrangeas at home have some cupped single leaves at the top of the plants too. A bad infestation can consist of 10 to 20 of these groups of cupped leaves. You will find a slender greenish caterpillar with a blackish head up to a ½-inch long if you pull the leaves apart.
Advertisement
Hydrangea leaftier emerges in the spring as a small brown-and-white patterned moth that you probably will not notice in the garden. Its eggs are laid at the branch tips of different hydrangea species but are commonly seen on Annabelle hydrangeas.
The hatching caterpillars web the leaves together and feed on the enclosed flower bud and surrounding leaves, which you are observing in your garden now. The larvae drop to the ground later in summer to pupate and emerge as adult moths the following spring.
The damage is generally minor, but a large number of cupped leaves is obvious and can be an aesthetic issue for some gardeners. A big infestation can also reduce flowering.
Generally, this is not a pest that needs to be controlled. You can carefully open the leaf pouches when you see them and smash the caterpillar inside or remove and destroy the infested leaf masses.
They are difficult to control by spraying, since they are protected by the leaves. You can use a single application of Bacillus thuringiensis kurstaki (DiPel is one trade name product) or a labeled pyrethroid, providing you can force the spray into the cupped leaves; otherwise, the sprays will not be effective.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.
