Asked November 06, 2020, 5:16 PM EST
Wayne County Michigan
There are several options you can try to gain control of hydrangea leaftiers (Olethreutes ferriferana). Fortunately the leaftiers do not harm the overall health to the plant but if not kept in check they can reduce the amount of blooms.
The following suggestions are from the link below obtained from Toronto master gardeners.
"The nests of the hydrangea leaf-tier are unlikely to cause long term damage to your hydrangeas, although they are unsightly and may cause particulars flower buds to abort. There are a number of ways you can deal with the problem. You can physically control the infestation by cutting off the infected leaves, by handpicking the caterpillars or crushing them inside their cocoons, or by opening the infected leaves to expose them to the sun. If the infestation is very serious you can cut back the stems of your hydrangeas in early spring or apply Bacillus thuringiensis, or BT, which is available in most garden centers."
If you try using BT it needs to be applied in early spring before the caterpillars take shelter in the leaves. If you had a large infestation this year than you certainly can try the option to prune the canes down to about 4- 6 inches in the fall or spring. Discard and destroy all debris from pruning. There are some species of hydrangeas that bloom on old wood and if you were to prune them down to the ground you would not see any blooms until the following year. Your Annabelle’s do not fall into this category since they bloom on current wood so pruning in the spring will help.
I following links will provide you with more information.
I hope this helps you out!