Tomato yellow leaf curl virus

also called TYLCV

Whitefly-carried, and it stops a tomato plant dead: leaves small, cupped and yellow-edged, flowers dropping, and no fruit at all after infection.

Virus No cure Spread by insects Spreads to neighbors

What you'll see

New leaves small, thickened and cupped upward, with the margins turning yellow.
The whole plant stunted and bushy, with shortened internodes so it looks compressed.
Flowers dropping before they set, and no fruit forming after the point of infection.
Fruit already set before infection ripening normally, which is the odd and useful detail.
Whitefly present in numbers on the leaf undersides.

Why it happens

A virus transmitted only by the sweetpotato whitefly. A whitefly that feeds on an infected plant for a few hours carries the virus for the rest of its life, and the plant shows nothing for two to three weeks. It does not travel on seed, on tools or by touch — the whitefly is the entire route, and controlling it is the entire answer.

Warm regions and greenhouses where whitefly is present year-round: the south, the southwest, Florida, and any protected structure. Late-planted tomatoes in a hot autumn take the worst of it. Northern outdoor gardens usually escape it entirely.

Treating it

There is no cure. Bag the plant where it stands, so the whiteflies on it do not fly to the next one, and remove it.
Deal with the whitefly on the remaining plants before they carry it on.
Check the rest of the row every week; the delay between infection and symptoms means the neighbors may already have it.
Do not plant a replacement tomato until the whitefly population is under control.
Clear weeds and volunteer tomatoes, which hold the virus between crops.

Keeping it away

Grow resistant cultivars — the Ty-1 through Ty-3 genes are in many modern hybrids and they work.
Raise or buy transplants under fine mesh; an infected transplant brings the disease straight into the bed.
Use reflective silver mulch, which genuinely reduces whitefly landings.
Hang yellow sticky traps to detect the whitefly flight early.
Keep a whitefly-free break in a greenhouse over winter rather than carrying plants through.

Who gets it

Tomatoes above all; also peppers, beans and many weeds that carry it between crops.