Most tomato leaf curl is physiological leaf roll: lower leaves roll upward, stay green, and feel leathery, and fruiting is barely affected. Leaves that curl down and twist point to herbicide, yellow cupped new leaves on a stunted plant suggest a virus, and twisted, bronzed tips suggest mites. Describe the curl below to find the likely cause.
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What Your Result Means: the checker names the most likely cause of the curl, how serious it is, and what to do. The shape of the curl and which leaves it starts on do most of the work; herbicide exposure and whiteflies raise or lower the odds of the more serious causes.
Why Are Tomato Leaves Curling?
Leaf curl has a handful of causes, and each leaves a different pattern. Look at which way the leaves curl, whether they stay green, and whether it starts on old or new growth.
- Look at the curl: rolled up, curled down and twisted, cupped and yellow, bronzed, or wilting.
- Note where it starts: lower leaves, the newest growth, or the whole plant.
- Think back: any new compost, manure, hay, or straw, or spraying nearby? Any whiteflies?
- Read the result and act, or send a sample to your local extension office if it looks serious.
What Each Result Means
| Result | What It Tells You |
|---|---|
| Likely cause | The most common cause of that pattern |
| How serious | Harmless, damaging, or plant-ending |
| What to do | Your first step |
| Prevent it | How to avoid it next time |
Tomato Leaf Curl Causes at a Glance
| What You See | Likely Cause | How Serious |
|---|---|---|
| Lower leaves roll up, stay green, feel leathery | Physiological leaf roll | Minor |
| Leaves curl down, stems twist, new leaves narrow | Growth-regulator herbicide | Serious; cannot be reversed |
| New leaves cupped and yellow-edged; plant stunted | Tomato yellow leaf curl virus | Serious; no cure |
| Tips twisted and bronzed; lower leaves fine | Broad mites | Damaging; treatable |
| Lower leaves bronzed; stem brown near soil | Tomato russet mites | Damaging; treatable |
| Leaves curl and wilt in dry soil or heat | Water or heat stress | Minor if fixed |
How Does the Leaf Curl Checker Work?
It matches the curl pattern to the cause extension services link it with, then adjusts for clues that make the serious causes more or less likely.
Down, twisted, strap-like new leaves -> herbicide injury
Cupped + yellow edges + stunted -> yellow leaf curl virus
Twisted, bronzed tips; lower leaves fine -> broad mites
Bronzed lower leaves -> tomato russet mites
Herbicide exposure or whiteflies -> raise those causes
Worked Example
Say the newest leaves on your plants are curling downward, the stems are twisting, and the new leaflets are narrow and strap-like, a few weeks after you spread fresh horse manure. The likely cause is herbicide injury: long-lasting pasture herbicides such as aminopyralid can pass through animals into manure. The damage cannot be reversed, but new growth may come in normal. Stop using that manure and ask your extension office about testing it before you plant there again.
Factors That Change the Result
- Weather and care: heat, drought, a wet spell, heavy pruning, and root damage from hoeing all trigger physiological leaf roll.
- Variety: indeterminate vining types roll more readily than determinate bush types.
- Region: yellow leaf curl virus is mostly a problem in the southern United States, where whiteflies survive winter.
- Inputs: compost, manure, hay, or straw from treated pasture can carry herbicides for a long time.
- Neighbors: growth-regulator herbicides can drift a long way from lawns and fields.
Understanding Your Outputs
| Output | Meaning | Best Used For |
|---|---|---|
| Likely cause | Best match for the pattern | Naming the problem |
| How serious | Effect on the plant and crop | Deciding how fast to act |
| What to do | First step | Acting today |
| Prevent it | Long-term step | Next season |
When to Use It
Use it as soon as you notice curling, especially on new growth, where the serious causes show first. If curling comes with wilting, try the Overwatered vs Underwatered Checker. For whiteflies, see our guide to whiteflies on tomatoes.
Common Mistakes to Avoid
- Treating physiological leaf roll: it is a stress response, not a disease, and sprays do nothing.
- Pruning off rolled leaves: they still feed the plant and shade the fruit.
- Reusing suspect compost or manure: herbicide residues can damage the next crop too.
- Keeping virus-infected plants: they will not recover and can be a source for whiteflies to spread.
- Missing mites: broad mites are too small to see without a hand lens, so damage is often blamed on something else.
Accuracy and Limitations
This is a guide to the most likely cause, not a lab diagnosis.
What It Does Well: separates the common harmless roll from the serious causes that need action.
What It Does Not Do: test for viruses or herbicide residues, or see mites. Several causes can overlap. For viruses and herbicide residues, a lab test through your extension office is the only sure answer. This is general guidance, not professional advice.
Methodology
Method: a rule-based match of curl pattern and location, adjusted for herbicide exposure and whiteflies. Physiological leaf roll: upward cupping and inward rolling of lower leaflets that stay green and leathery, with minimal effect on fruit production (Clemson HGIC); the most common cause of tomato leaf curl (University of Missouri IPM). Herbicide: downward rolling and twisted growth that cannot be reversed (Clemson); drift of 2,4-D or dicamba and compost containing picloram, clopyralid, or aminopyralid (Missouri), which pass through livestock into manure and persist through composting (NC State Extension). Virus: tomato yellow leaf curl virus, spread by whiteflies, mostly in the southern United States (NC State Extension). Mites: broad mites on young growth, treatable with horticultural oil or sulfur (University of Maryland Extension); tomato russet mites starting low on the plant (University of Kentucky). No dosing: follow product labels and your extension office.
Sources: Clemson HGIC – Tomato Leaves Rolling?, University of Missouri IPM – Tomato Leaf Curl, NC State Extension – Tomato Yellow Leaf Curl Virus, University of Maryland Extension – Broad Mites on Tomatoes, University of Kentucky – Tomato Russet Mite, NC State Extension – Herbicide Carryover in Hay, Manure, Compost, and Grass Clippings. Last reviewed: September 28, 2026 · Reviewed by Aiza Anwar.
Frequently Asked Questions
Why are my tomato leaves curling up?
Upward rolling of green, leathery lower leaves is usually physiological leaf roll, a stress response to heat, heavy pruning, root disturbance, or big swings in water. The University of Missouri calls it by far the most common cause of tomato leaf curl, and Clemson notes it has minimal effect on fruit production.
Why are my tomato leaves curling down and twisting?
Downward curling with twisted stems and narrow, strap-like new leaves points to growth-regulator herbicide injury, from drift of products such as 2,4-D or dicamba, or from compost, manure, or hay carrying long-lasting herbicides such as clopyralid or aminopyralid.
Is tomato leaf curl harmful?
Physiological leaf roll is not: the plant keeps growing and fruiting. Herbicide injury, virus, and mites are more serious, so it is worth identifying the cause.
Can herbicide damage on tomatoes be reversed?
No. Clemson Extension notes herbicide injury cannot be reversed, but if the plant is not killed, new growth may come in normal. Stop using any compost or manure you suspect.
What is tomato yellow leaf curl virus?
A virus spread by whiteflies that causes yellow, cupped new leaves, a stunted, bushy plant, and flower drop. It is found mainly in the southern United States. There is no cure; remove infected plants and grow resistant varieties.
Can mites make tomato leaves curl?
Yes. Broad mites, too small to see without magnification, twist and curl the youngest leaves while lower leaves stay normal. Tomato russet mites start lower on the plant, bronzing leaves and browning the stem.
Should I prune curled tomato leaves?
Not for physiological leaf roll, since the leaves still feed the plant. Remove leaves only when they are diseased or heavily infested.
Can too much or too little water cause leaf curl?
Yes. Big swings in soil moisture are one of the stresses behind physiological leaf roll, and leaves also curl and wilt in dry soil. Water deeply and evenly and mulch.
Can compost or manure cause tomato leaf curl?
Yes, if it contains long-lasting pasture herbicides such as picloram, clopyralid, or aminopyralid, which pass through animals and survive composting. Ask where your compost, manure, hay, or straw came from.
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See the Full Problems & Solutions Guide
This checker gives general guidance on the likely cause of tomato leaf curl, not a lab diagnosis or professional advice. Viruses and herbicide residues can only be confirmed by testing; contact your local extension office. Follow product labels for any treatment. Spotted an error? Tell us here.