Impatiens necrotic spot virus

Impatiens necrotic spot orthotospovirus

also called INSV

The greenhouse twin of tomato spotted wilt: thrips-carried, incurable, and usually arriving on a bought bedding plant rather than blowing in.

Virus No cure Spread by insects Spreads to neighbors

What you'll see

Brown or black ringspots and irregular dead patches on the leaves, often with a target-like pattern.
Black streaks running along leaf stalks and stems.
Sudden collapse of the growing tip while the lower plant looks well.
Stunting and one-sided growth, with the plant simply refusing to get away.
Symptoms varying wildly between plant species, which is exactly what makes it hard to recognize.

Why it happens

A virus carried only by western flower thrips, and only by thrips that fed on an infected plant while they were larvae. That is why it is a greenhouse and nursery disease above all: the whole cycle needs a place where thrips breed continuously on infected plants, and a garden usually acquires it as a finished bedding plant with the virus already in it.

Greenhouses, tunnels, propagation benches and the trays of bedding plants that come out of them. Once outdoors it spreads slowly or not at all, because the thrips cycle is broken by winter over most of the continent.

Treating it

There is no cure. Bag and remove the plant, thrips and all.
Inspect everything else that came from the same tray or the same supplier.
Control the thrips in the greenhouse — blue sticky traps, predatory mites, and a clean break between crops.
Do not take cuttings from a suspect plant.
Clear weeds under the benches, which are where thrips and virus overwinter together.

Keeping it away

Inspect bedding plants at the nursery for ringspots and black stem streaks before buying.
Quarantine new plants for two or three weeks before they join a greenhouse.
Keep the greenhouse thrips-free with sticky traps and biological controls rather than sprays.
Empty and clean the greenhouse completely once a year to break the continuous cycle.
Grow bedding from your own seed where the disease has been a recurring problem.

Who gets it

Impatiens, begonia, cyclamen, gloxinia, coleus and many other bedding and greenhouse plants; also lettuce, tomato and pepper.