Hydrangea leaf curl with worm inside

(Question)

What do I clean soil with. Did not remove leaves until most worms were gone. Not sure what to do now.

(Answer)

Our guess is that your hydrangea has been infected by the caterpillars of either the Hydrangea leaftier (Olethreutes ferriferana), or leafrollers.

In an leaftier infection, 3 or 4 cupped leaves are tied together with silk; these are located at the tip of the branches and the top of plant. There are typically 10 to 20 of such pouches found per infected plant. If you unfurl the leaves, you will find a slender green caterpillar with a blackish head. It feeds on the bud and leaves in its “pouch” then drops to the ground and tunnel into the soil to pupate in the summer, emerging as an adult moth in the following spring. It then lays eggs onto the Hydrangea, repeating the cycling all over again.

In contrast, the leafroller caterpillar binds only one leaf. Like the leaftier, it feeds on the leaf then drops to the soil to pupate.

If left unchecked, an infestation of these caterpillars will result in lost flower buds and limits the season’s bloom. But the damage is largely cosmetic and the shrub itself usually recover from the infestion by the following year.

Early detection is key in controlling the infestion. In spring, check the shrub regularly; remove all infected leaves and destroy. Alternatively, unfurl the leaves and remove and kill the caterpillars. If the caterpillars are already gone (i.e. pupating in the ground), there is not much you can do at that point. Clean up the ground thoroughly around the hydrangea shrub.