Tomato spotted wilt virus

Tomato spotted wilt orthotospovirus

also called TSWV

Bronzed leaves, dark stem streaks and ripe fruit blotched with pale concentric rings — carried by thrips, and incurable once a plant has it.

Virus No cure Spread by insects Spreads to neighbors

What you'll see

Young leaves bronzed or purple-brown, with small dark spots, and the growing tip curling inward.
Dark brown or black streaks running along the stems and leaf stalks.
Concentric pale rings and blotches on ripening fruit — yellow on a red tomato, so the fruit looks target-marked.
One-sided growth, or a whole plant stunted and off-color beside healthy neighbors.
Peppers with necrotic ringspots and lettuce with brown spotting on one side of the head.

Why it happens

A virus that is carried only by thrips, and only by thrips that fed on an infected plant as larvae — an adult that picks it up cannot pass it on. That detail is why controlling adult thrips in the crop does so little and why keeping the virus out of the seedling stage does so much. It does not travel on seed or on tools.

Worst where thrips overwinter or breed continuously: greenhouses, tunnels, and mild-winter regions. Weedy edges and ornamental bedding — especially impatiens, petunias and chrysanthemums — hold the virus over from year to year and are usually where an outbreak starts.

Treating it

There is no cure. Pull and bag infected plants as soon as you are sure, before the thrips on them can carry it on.
Bag the plant where it stands rather than carrying it through the garden shedding thrips.
Do not replant a tomato in the same spot until you have dealt with the thrips source, which is usually a weed or an ornamental nearby.
Check the rest of the row weekly; the symptoms show two to three weeks after infection, so the neighbors may already carry it.
Control the thrips in the greenhouse rather than in the bed — that is where the cycle is being completed.

Keeping it away

Grow resistant cultivars, which exist and work: look for the Sw-5 gene in tomatoes and Tsw in peppers.
Keep seedlings under fine mesh or in a thrips-proofed frame; infection at the seedling stage is the worst kind.
Clear weedy edges and do not overwinter chrysanthemums, impatiens or petunias next to where the tomatoes will go.
Hang blue sticky traps in the greenhouse to catch the flight early, and act on what they tell you.
Keep the minute pirate bugs and predatory mites that hunt thrips, rather than spraying them out.

Who gets it

Tomatoes, peppers, aubergines, lettuce and potatoes, plus a long list of ornamentals — impatiens, petunia, chrysanthemum, dahlia and begonia.