Hydrangea Pest: Hydrangea Leaf-Tier

If you have a smooth hydrangea in your yard (like an Annabelle or Incrediball), you may have encountered a peculiar pest known as the hydrangea leaf-tier. These tiny troublemakers can wreak havoc on the leaves of your beloved hydrangea plants, but fear not! Rarely do these little caterpillars do major damage to your plants, but a larger infestation will likely reduce your blooms.  

The hydrangea leaf-tier (Olethreutes ferriferana) is actually a small moth that is native to Canada and the US. They’re typically brownish-gray and have a wingspan of about half an inch. While the adult moths are harmless, it’s the larval stage that causes annoyance for hydrangea enthusiasts.

What’s Wrong With My Hydrangea Leaves? 

The telltale sign your hydrangeas might be affected by the leaf-tier are leaves that appear to be sewn or bound together with fine silk threads. These tightly woven leaves create a cozy shelter for the leaf-tier larvae, protecting them from predators such as birds and insects, and creating a microclimate that offers favourable conditions for the larvae’s development, including a regulated temperature and increased humidity.

Where do Leaf-Tiers Come From?

The leaf-tier larvae emerge from eggs laid on hydrangea leaves during late spring or early summer by adult moths. Once hatched, the tiny larvae begin to construct their unique shelters in your hydrangea leaves. As they grow, the larvae continue to feed on the leaves within their protective leafy fortresses, gradually causing damage to the plant blooms. Once they’re ready to pupate they will drop to the ground and overwinter there until they emerge as moths early the next spring to fly around and start the cycle all over again. 

How to Control Hydrangea Leaf-Tier

If you have a really large hydrangea, and don’t mind less blooms or don’t have the time to work on this, you can choose to do nothing at all. This pest will rarely result in the death of a plant. Here are our top suggestions on how to control the hydrangea leaf-tier:

Physical Controls:

• Peeling Open the Leaves – For more targeted control you can carefully peel open the sealed leaves to find the larvae hidden inside. You can dispose of the larvae by squishing or dropping into some soapy water. This method allows for direct intervention and can be particularly effective when dealing with a limited number of infested leaves. Typically doing this a couple times in early spring will save your hydrangea blooms.
• Manual Removal – You can snip off any sealed leaves, disposing of the pockets by stepping on them or soaking in a bucket of soapy water. This will also be cutting off flower buds, but is a faster method. 

Chemical Controls:

If physical control methods prove ineffective, you can try using Bacillus thuringiensis var. kurstaki (Btk), a naturally occurring bacteria-based insecticide. Btk specifically targets caterpillar-like pests, including leaf-tiers. This will be ineffective once the caterpillars are inside their leaves though as they eat the new leaves that emerge inside of their little home, so it should be applied early in the season right as larvae are emerging. Btk is non-specific with the caterpillars it will impact (such as beneficial caterpillars of other butterflies and moths), so take care to avoid other plants and as always, follow safety guidelines when applying any insecticide. 

Additional Action:

There are a few other things you can do such as encourage natural predators (biological controls) like birds, parasitic wasps and lacewings that feed on leaf-tiers by creating a bio-diverse garden. And remember that an ounce of prevention is worth a pound of cure! Help prevent infestations by doing a good clean up in the fall underneath your hydrangeas. This can reduce the number of pupating larvae in the soil. Cutting the stems down in the early spring as preventative measures to reduce the overall numbers once eggs have been laid is helpful as well. For more detailed info on how to clean up your hydrangeas, check out our garden guide on How to Prune Hydrangeas for more tips!

So What’s Next?

Armed with some of this information, hopefully you can find a balance with these pesky pests and enjoy lovely blooms on your smooth hydrangeas for years to come!