Tomato leaf curl

Signs to look for

1. Physiological leaf roll: the lowest, oldest leaves roll upward at the margins until they touch or overlap.
2. Those rolled leaves feel firm and leathery, and they do not unroll again once they have rolled.
3. The plant may look wilted while flowering and setting fruit perfectly normally, which is the reassuring detail.
4. Virus instead: the newest leaves are small, cupped upward, crumpled, and yellow along the margins and between the veins.
5. Virus instead: the plant is stunted, upright and bushy from shortened internodes, and flowers drop without setting fruit.
6. Virus instead: whiteflies present on the leaf undersides, which is how the virus arrives.

What it gets mistaken for

Fusarium wilt. Fusarium wilt yellows and wilts one side of the plant and leaves brown streaks in the stem when it is cut. Neither form of leaf curl does either.

Drought wilt. A thirsty plant droops softly and recovers within hours of watering. Rolled leaves are firm and leathery and stay rolled.

Aphid damage to new growth. Aphids distort new leaves too, but they leave colonies, honeydew and cast skins, and the plant is not stunted or bushy.

Plants it affects

Tomatoes, where both causes are common, Other vegetables affected by physiological leaf roll in the same conditions, Greenhouse and field tomato crops where whiteflies are active, for the viral form.

How to treat it

From the gentlest step upward. Move to the next step only if the one before it has not worked within a week or two.

1. Work out which one you have first, because the two answers are opposite. Older lower leaves rolling upward, firm and leathery, on a plant that is flowering and fruiting normally, is physiological leaf roll.
2. For physiological leaf roll, no action is needed. Extension guidance is direct that it will not harm plants and does not damage the fruit that develops later. Symptoms fade as temperatures even out and soils dry.
3. Water evenly and mulch to steady the soil moisture the plant is responding to, and go easy on heavy pruning.
4. If it is the new growth that is small, cupped, yellow-margined and crumpled, with a stunted bushy plant and flowers dropping, check leaf undersides for whiteflies and treat it as a virus.
5. Remove virus-affected plants and dispose of them away from the crop rather than composting them. Infected plants do not recover, and leaving them in place keeps supplying whiteflies with virus to carry.
6. Manage whiteflies as the actual control point: virus-free and whitefly-free transplants, fine-mesh exclusion screening, reflective mulch to repel them, and removal of old crop residue and volunteers.
7. Plant TYLCV-resistant varieties where the virus is established locally. No product cures a virus-infected plant, so for any whitefly treatment follow the product label and check your local extension service for what is registered where you grow.

How to keep it away

• Keep soil moisture steady with mulch and even watering rather than swinging between saturated and dry.
• Use virus-free and whitefly-free transplants, and inspect leaf undersides before planting.
• Grow TYLCV-resistant varieties where the virus is present, and exclude whiteflies from young plants with fine mesh or reflective mulch.
• Clear old crop residue and volunteer tomato plants, which carry both whiteflies and the virus between seasons.

Related problems

• Fusarium wilt: Fusarium wilt is a soil-borne fungus that enters through the roots and blocks the plant's water-conducting tissue.

Sources

• UC IPM: Physiological Leaf Roll in Vegetables (Home and Landscape)
• NC State Extension: Tomato Yellow Leaf Curl Virus
• UC IPM: Tomato Yellow Leaf Curl, Tomato Pest Management Guidelines