Why Are My Shrub Leaves Curling? Common Causes
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Why are my shrub leaves curling? Leaf curl is a symptom, not a diagnosis. It can follow feeding by sap-sucking insects, damage from leaf-rolling caterpillars, or other stresses that change how new leaves develop. The two sources used here are a university Q&A on viburnum and hydrangea leaves and a North Carolina Cooperative Extension pest alert on curling leaves of trees and shrubs. Together they point to a short checklist: look under the leaves, check for insects, and review the recent care the plant has received.
Quick answer
- Uncurl a few leaves and look at the underside for insects, eggs, or damage. This is the first check the Ask Extension answer recommends.
- Sap-sucking insects such as aphids and leafhoppers can distort newly emerging leaves and leave sticky residue.
- Leaf-rolling caterpillars can roll leaves into cups. One Q&A answer links a hydrangea’s rolled leaves to a leaf roller moth.
- Recent fertilizer or herbicide use nearby is a question to answer before you choose a treatment.
How we chose
We chose one university question-and-answer page and one county extension pest alert. The first is an Ask Extension entry from a gardener describing curled leaves on several shrubs, including a viburnum and a hydrangea. The second is a North Carolina Cooperative Extension pest alert written for curling leaves on trees and shrubs. Both pages were opened on 2026-10-27. We did not use retail or forum sources.
Start with the underside of the leaf
The Ask Extension expert asks a gardener to uncurl a leaf and look at the underside to see if there is damage or insects. That question is the most useful first step. Curling can look dramatic from above, but the evidence is often on the underside of the leaf, where insects feed and lay eggs. A magnifying lens helps if the pests are very small.
In the example, the gardener uncurled a leaf and saw a dark smudge, but reported no damage on the underside. Write down what you see on each leaf you check so you can compare them.
Sap-sucking insects that distort new leaves
The North Carolina pest alert explains that leafhoppers and aphids both use needle-like mouthparts to suck juices from leaves. When these insects feed on newly emerging leaves, the leaves can become distorted. The alert adds that leaves can curl mildly or even severely. In one example the county agent describes, at least fifty percent of a tulip poplar had distorted leaves, and high numbers of aphids and leafhoppers were present.
The same pest alert describes a second effect. These insects take in sugary sap and secrete sticky droppings on leaves and nearby objects. That sticky residue can support sooty mold, a dark coating that the alert describes as a nuisance. If you see sticky leaves along with curled new growth, sap-sucking insects are a more likely cause than a disease that does not produce residue.
The pest alert covers trees such as poplar, catalpa, sweetgum, and locust. Those trees are not shrubs, so the example is useful for the general pattern but does not prove the same insects are present on your shrub. Check your plant before you assume the pattern applies.
Leaf rollers that roll leaves into cups
Not all curling is caused by feeding. In the Ask Extension answer about several bushes, the expert states that the leaves of the hydrangea appear to have been rolled into cups by the hydrangea leaftier or leaf roller moth. Leaf rollers wrap or fold leaves around the larvae that feed inside. A rolled leaf that is cup-shaped and holds a caterpillar can look different from a leaf that is curled by a sap-feeding insect.
The gardener noted that the affected leaves were all new growth since the bushes had been pruned the previous fall. That detail matters because pruning can change the timing of new leaves, and the pests that feed on them may appear at a predictable point in the season. Keep a note of when your plant was last pruned and when the curling began.
Check recent fertilizer, herbicide, and watering
The Ask Extension page asks whether fertilizer or herbicide has been applied around the plants or on a nearby lawn. This is an important question because chemical drift and fertilizer can distort new growth. The gardener in the example said fertilizer had been applied to nearby grass, but the shrubs were separated from the lawn by a driveway and landscaping. The expert still treated the question as worth asking.
The same page also asks whether the plant received the same amount of water as in previous years, and whether there has been a soil test recently. Those questions point to watering and soil conditions as possible contributors. The sources do not give a watering schedule for shrubs, so use your own knowledge of the plant and local conditions to judge whether water has been a problem. Leaves can also roll in response to water stress, which is a separate process from insect damage; see how grass leaves roll up during drought for that mechanism.
Practical steps you can take now
Start by taking photos of several leaves and the new growth on the plant. Check the underside of at least three curled leaves for insects, eggs, and sticky residue. If you find a caterpillar inside a rolled leaf, the leaf roller explanation from the Ask Extension page is the more likely cause. If you find many small sap-feeding insects, the North Carolina pest alert describes the damage they produce.
Review the last few months of care. Note any fertilizer, herbicide, or pruning, and note how the weather has changed. Compare the affected shrub with a nearby plant of the same kind, if you have one. If only one plant is affected, the cause may be local. If several different shrubs show the same symptom, a broader cause is more likely.
For a background explanation of why insects that suck sap can distort leaves, see how aphids feed on phloem without clogging sieve tubes. It explains the feeding mechanism in more detail than either source does.
What we could not verify
Neither source confirms the cause of the curling on your particular shrub. The Ask Extension answer is based on a description and photographs from one gardener, and the pest alert describes trees rather than shrubs. We have not claimed that a single cause applies to every case of leaf curl. The sources also do not say how much curling is harmful to the long-term health of a shrub.
What the sources do not say
The sources do not give a treatment schedule, a list of approved products for these insects, or a rate for any spray. They do not say how long curled leaves take to recover after the cause is removed. Check the product label or ask your local extension office before you apply any treatment.
Frequently asked questions
Is leaf curl always caused by insects?
No. In the Ask Extension example, the gardener found no damage on the underside of the leaf, and the expert still asked about fertilizer, herbicide, and water. The pest alert describes insect feeding as one common cause, so several possibilities need checking.
What does a leaf roller do to a shrub?
The Ask Extension answer says the hydrangea leaves appeared to be rolled into cups by a leaf roller moth. Leaf rollers wrap or fold leaves, and the rolled leaf can look very different from a leaf that is curled by sap-feeding insects.
Why are my leaves sticky when they curl?
The North Carolina pest alert explains that aphids and leafhoppers take in sugary sap and secrete sticky droppings. That residue can lead to sooty mold, which the alert describes as a nuisance on leaves and nearby objects.
Should I check for herbicide damage first?
Ask whether herbicide or fertilizer was applied nearby, as the Ask Extension page does. The sources do not give a rule for how far away drift can travel, so use your own records of recent applications to decide.
What should I do if the leaves keep curling?
Keep checking the underside of new leaves for insects and rolled leaves. If the pattern continues, bring photos and a list of recent care to your local extension office. The sources do not give a single fix for all cases.
Sources
- Ask Extension, “Question #867990: Several of our bushes have leaves that are curling up,” https://ask.extension.org/kb/faq.php?id=867990 (opened 2026-10-27). Quote: “It would appear that the leaves of the hydrangea have been rolled into cups caused by the hydrangea leaftier or leaf roller moth.”
- North Carolina Cooperative Extension, Henderson County Center, “Pest Alert: Curling Leaves on Trees and Shrubs,” https://henderson.ces.ncsu.edu/news/pest-alert-curling-leaves-trees-shrubs/ (opened 2026-10-27). Quote: “When the insects feed on newly emerging leaves the leaves can become distorted.”
