Why are my tomato leaves curling?
Tomato leaf curl has three main causes — heat stress, herbicide drift, or a virus — and the curl pattern and which leaves are affected help narrow down which one you're dealing with.
Physiological leaf roll is the benign version and the most common: leaves curl upward along their length, usually on the lower third of the plant, during hot afternoons. The plant is managing water loss. If the leaves uncurl in the evening or the next morning, and the affected leaves are otherwise green and healthy-looking, this is normal behavior. No action is needed beyond consistent watering and mulch to moderate soil temperature.
Herbicide drift is the cause gardeners often miss. If leaves are curling, twisting, or showing a cupped shape along with abnormal growth — new leaves coming in distorted, stems thickening or curling in a corkscrew pattern — a broadleaf herbicide drifted onto the plant is the likely cause. This can happen from a neighbor's lawn treatment on a windy day or from a sprayer that wasn't fully cleaned after herbicide use. Mildly affected plants often recover in 4–6 weeks; severely affected plants typically don't fully recover and produce oddly-shaped fruit.
Tomato mosaic virus and tomato yellow leaf curl virus both cause leaf distortion. With virus-caused curl, you typically see: leaves that curl downward (not upward), mosaic yellowing or mottling on the leaves, stunted growth throughout the plant, and no recovery regardless of conditions. These viruses are spread by aphids (mosaic) or whiteflies (yellow leaf curl). There is no cure — remove and bag affected plants to slow spread, and control the insect vectors on remaining plants.
Check the new growth to narrow things down. If the newest leaves at the growing tip are normal, the problem is likely heat stress or a past exposure. If the newest growth is distorted, a virus or herbicide effect is more likely.
- AnthracnoseSunken, dark circular lesions on ripening fruit, sometimes with salmon-colored spores in the center.
- AphidSoft, clustered insects on new growth causing curled leaves and sticky honeydew.
- Black RotV-shaped yellow lesions at brassica leaf margins with blackened veins inside — a bacterial disease that moves through the vascular system.
- Blossom End RotDark, sunken, leathery patch on the blossom end of tomato or pepper fruit — a calcium deficiency disorder.
- Brown Marmorated Stink BugSunken, corky dimples on fruit and pods caused by a mottled brown shield bug feeding through the skin.
- Why are the lower leaves on my tomatoes turning yellow?Lower-leaf yellowing on tomatoes is most often early blight, normal leaf senescence, or nitrogen deficiency — the pattern and timing tell you which one you're dealing with.
- Why are my cucumber leaves puckered, crinkled, or distorted?Puckered or crinkled cucumber leaves usually mean a mosaic virus (spread by aphids) or severe aphid feeding itself — check the undersides of leaves for aphid colonies before concluding it's a virus.
- I have aphids on multiple plants — do I need to spray everything?Aphids tend to colonize plants under stress and naturally crash when beneficial insects find them — water sprays and patience are often more effective than pesticides.