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INSV (Impatiens Necrotic Spot Virus) and Western Flower Thrips In the Greenhouse

Christine Casey, Extension Entomologist

CAUTION: This information was developed for North Carolina and may not apply to other areas.

Frankliniella occidentalis (Pergande), Thripidae, THYSANOPTERA

I N S V on leafThe tospoviruses are a group of plant-infecting viruses that are transmitted by several species of thrips.  These insects are small, highly mobile, and distributed worldwide.  INSV affects primarily flower crops and is vectored by western flower thrips.  Infected plants cannot be cured and must be destroyed. Disease incidence does not correspond to thrips density, so merely monitoring insect populations is not sufficient to predict epidemics. Thrips can only acquire the virus if they feed on an infected plant during their first larval stage, but generally only transmit the disease to other plants when they are adults.

In addition to plant foliage, thrips feed on pollen and flower petals, which causes pale spots that progress to necrotic patches and causes premature aging of blossoms.  Damaged leaves will be puckered and distorted if the thrips feed on them while still buds.  Since these symptoms are similar to those with other causes, it is important to obtain a diagnosis as soon as possible.  This can be done by the Plant Disease and Insect Clinic at NCSU.

Thrips can be introduced into a greenhouse on plant material, blown in from outside hosts, or inadvertently carried by workers.  More information on thrips biology can be found in Insect Note 72. Virus symptoms are variable and mimic other diseases or nutritional disorders, and symptoms may not appear on infected plants for 10 to 14 days after thrips feeding.


There is no cure for an INSV-infected plant. The thrips vector is also difficult to manage.  Western flower thrips move deep into unopen buds where they are protected from pesticide sprays.  High volume wet sprays are most effective for this reason.  Systemic pesticides do not significantly affect thrips in the flowers.  A comprehensive control program is required to be effective.

  1. Remove weeds in and around the greenhouse to the extent possible.  Treat these for thrips as well.
  2. Do not wear light blue, white, or yellow clothing into the greenhouse.  Thrips may jump onto clothing and be carried to other benches or other greenhouses.
  3. Use yellow sticky cards placed with the top 2/3 of the card above the plant tops.  Use two cards per 5000 ft2 of greenhouse area.
  4. Screen greenhouse vents and air intakes to exclude thrips from entering the greenhouse.
  5. Immediately rogue virus-infected plant material.  Quick test kits to confirm virus diagnosis are available from Agdia (www.agdia.com).  The first time you use one of these kits, it is recommended that this diagnosis be confirmed by submitting a sample to the Plant Disease and Insect Clinic at NCSU.
  6. Follow label directions for pesticide application frequency.
Use a rotation of pesticides from different mode-of-action groups.


A suggested pesticide rotation for thrips is Conserve, Avid (suppression only), Pedestal (only kills immature thrips), and Azatin.  Mesurol is also effective for thrips control but has a 24 hour re-entry interval so its’ utility may be limited.  Thrips tend to develop pesticide resistance easily so rotation of materials is essential.  The North Carolina Agricultural Chemicals Manual lists these and other pesticides labeled for thrips management.

Biological Control

Biological control of western flower thrips with the predatory mite Neoseiulus cucumeris (Cucumeris) is being used successfully in bedding plant production. Introductions should start at the same time the crop is placed in the greenhouse.  Beauveria bassiana is an insect pathogen sold as the biopesticide BotaniGard® that is best used when thrips pressure is low.  Biological control is not recommended once a tospovirus outbreak has been confirmed.

Helpful Links

Minnesota WFT Note http://www.extension.umn.edu/distribution/horticulture/DG7374.html
The Complete Tospovirus Resource Page (K-State)

Recommendations for the use of screening materials and chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use screening are responsible for ensuring that air flow is adequate to ventilate the structure properly in hot weather.

Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service

Published by North Carolina Cooperative Extension Service
© 2002 NCCES

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Original version prepared by: James R. Baker, Extension Entomologist

Ent/ORT-120 June/2000; revised November 2002, January 2007 by Christine Casey
Web page last reviewed January, 2007 by the webperson.