Hi Erica -

Thanks for contacting the UVM Extension Master Gardener Helpline! The plant diagnostic worksheet and photos are helpful, so thank you for providing those.

For the suspected aphids last summer, did you see them on the leaves of the plant?

Leaf curl and reduced leaf development in Korean Spice Viburnum (Viburnum carlesii), especially when symptoms show up early in spring and repeat across seasons can be caused by a variety of issues. Below are likely causes with steps you can take to narrow things down or address the problem.

1. Aphids or Viburnum Leaf Beetle
These pests feed on new growth and can cause distorted, curled leaves. If the damage appears immediately in spring, it may be the result of eggs laid on stems the previous fall.

What you can do:

• Check for small insects on new stems and leaves.

• If you see active aphids, apply insecticidal soap or neem oil.

• Use dormant oil spray next winter (before bud break) to reduce overwintering eggs.

• More information is available from the University of Minnesota Extension (https://extension.umn.edu/yard-and-garden-insects/aphids).

2. Root or Environmental Stress
If the shrub flowers but does not fully leaf out, it may be under root stress. Poor drainage, soil compaction, or winter root injury can reduce foliage without affecting flowering.

What you can do:

• Confirm that the root flare is visible and not buried.

• Check the root zone for signs of rot, girdling roots, or vole activity.

• Ensure the site drains well after rain and is not staying soggy.

• Apply mulch 2 to 3 inches deep, but keep it pulled back from the trunk.

3. Disease (Viral or Fungal)
Some diseases, such as powdery mildew or certain viruses, can deform leaves. However, these typically show additional symptoms such as leaf spotting or discoloration.

What you can do:

• Watch for changes in leaf color, spotting, or new patterns of damage.

• If symptoms spread or worsen, lab testing may be necessary.

• You can find more detailed information in this Cornell guide to Viburnum pests and diseases (PDF)(https://ecommons.cornell.edu/server/api/core/bitstreams/4a6b3420-aa35-4028-acfa-092c0418b01f/content)

4. Herbicide Drift
Some herbicides cause leaf curling when they drift onto non-target plants. This often shows up on a few shrubs in early spring, especially near treated lawns or edges.

What you can do:

• Have herbicides been applied nearby recently?

• Look for similar symptoms on other plants in the same area, especially downwind.

Growing Conditions Reminder
Viburnums prefer well-drained, slightly acidic soil with even moisture. They do best in full sun to part shade. Stress from poor site conditions can compound other issues and make the plant more vulnerable to pests and diseases.

Next Steps

• Monitor for active pests this season and treat only if needed.

• Check root health and drainage.

• Maintain consistent soil moisture during dry spells.

• Continue observing for changes in symptoms.

Please feel free to follow up with what you find. We’re happy to help you troubleshoot further as the season progresses.