Impatiens Necrotic Spot Virus (INSV) & Western Flower Thrips: A Greenhouse Crisis

INSV and its relative Tomato Spotted Wilt Virus (TSWV) have devastated greenhouse crops. But growers who aggressively control thrips, inspect incoming plants, and maintain crop health can avoid losses.

INSV: The Virus

Symptoms vary wildly: wilting, stem death, stunting, yellowing, poor flowering, 'chicken pox' sunken spots, ring spots—or no symptoms at all. Depends on infection timing, plant age/state, greenhouse conditions, virus strain. Visual diagnosis is impossible. Lab testing (ELISA, PCR) required.

INSV Management

• Inspect all incoming plants; isolate suspicious ones immediately
• Isolate all incoming plants until confirmed virus-free
• Don't commingle sources; keep each source group separate
• Destroy infected plants—no cure
• No vegetative propagation from infected plants

Western Flower Thrips: The Vector

Detection

• Inspect incoming plants (check white/yellow flowers); isolate
• Hand lens + tap test over white paper
• Yellow/blue sticky cards at crop height: 1–3 per 1000 sq ft; near vents/doors
• Change cards regularly; wrap used cards in cellophane; record weekly counts
• ID help: state Dept. Ag, Extension, university entomology

Thrips-Virus Dynamics & Control

• Single spray fails. Apply at 5-day intervals (per label)
• One pesticide class per thrips generation (2–3 apps over 14–15 days), then rotate to different class
• No tank mixes of different chemicals
• Eggs laid in tissue (protected); hatch 3–4 days
• Larvae acquire virus but don't transmit; retain until adulthood
• 2nd larva → soil/litter → adults emerge 2–5 days later; live 30–45 days, transmit throughout
• Viruses not transmitted to eggs; each generation must feed on infected plants
• Spray timing: 1st kills winged adults; 2nd/3rd kill new wingless emergents
• Thorough coverage essential; rotate fogging and spraying

No INSV/TSWV-infected plants = no crop loss from this virus, even if thrips present.

Thrips Control Materials

Consult state Dept. Ag inspector or university entomologist for registered/recommended products on your crop.

Sanitation Essentials

• Strict thrips control on all greenhouse plants
• Eliminate all weeds in/near greenhouse
• Remove untended plants (thrips/virus reservoirs)
• Western flower thrips survive outdoors in PA and similar climates

Partial Host List (INSV/TSWV)

African violet, cyclamen, pea, ageratum, cymbidium, peony, alstroemeria, dahlia, periwinkle, amaryllis, delphinium, peppers, anemone, dracaena, petunia, aster, Easter lily, phlox, aubrietta, eggplant, plectranthus, azalea, endive, poppy, begonia, exacum, primrose, blue daze, forget-me-not, ranunculus, brassaia, fuchsia, romaine, browallia, gaillardia, salvia, calceolaria, gardenia, schefflera, calendula, geranium (ivy, diploid, tetraploid), shamrock, calla lily, gerbera, snap bean, carnation, gladiolus, snapdragon, cauliflower, gloxinia, speedwell, centranthus, gypsophila, statice, chicory, hydrangea, stephanotis, china aster, impatiens (NG, balsam), stock, Christmas peppers, kalanchoe, streptocarpus, chrysanthemum, lettuce, sweet pea, cineraria, Asiatic lily, tiger lily, coleus, Easter lily, tomato, columbine, lobelia, verbena, campanula, marigold, yucca, coriander, mimulus, zinnia, cosmos, morning glory, zygocactus, nasturtium.