Wednesday, March 4, 2009

Greenhouse - Chemical Control of Thrips

Thrips are a major insect pest in greenhouses and are notorious for transmitting viruses such as INSV. The following are some guidelines for controlling thrips with insecticides.

For growers using pesticides to manage thrips, plan to treat in the early evening. Thrips have two mass flights per day, so sprays in the early evening may contact more thrips. Small droplet sprays, repeated applications (two to three sprays about 5 days apart) and treating before you see a peak in adult numbers on yellow sticky cards are critical. Adult thrips numbers on cards tend to peak every two to three weeks. Apply insecticides before this peak, so adults will be killed before they lay eggs. A mass aggregretion pheromone or thrips lure is also available to be placed into sticky cards to aid in early detection of thrips.

To manage thrips, shorten spray intervals to 4-5 days and rotate pesticides with different modes of action. Some options for management (based upon grower feedback) include Avid (abamectin-group 6) tank mixed with Azatin (azadirachtin- Group 18B), Mesurol (methiocarb-group 1A), Pedestal (novaluron-group 15) tank mix with Pylon (chlorfenaphyr- group 13), Safari (dinotefuran Group 4A) and Conserve (spinosad-group 5). Overture (pyridalyl) (unknown mode of action) has contact, translaminar and some ingestion activity and can be added into your rotation program. It is labeled for thrips and caterpillars but may take from 7 to 14 days before you see control.

Horticultural oil (Pure Spray Green, Saf-T-Side, or Ultra fine oil) may also be an option provided label cautions regarding plant safety are followed. Note that Mesurol has a 24 hour REI plus it may leave an unsightly residue and Pedestal is an IGR labeled for immature stages. In addition, TriStar (acetamiprid - group 4A) or Aria (flonicamid - Group 9C) may help suppress thrips.
Growers often ask about adding sugar to their spray for thrips management. Recent research by Raymond Cloyd, Kansas State University showed that the addition of brown sugar and other sweeteners to lure thrips from hiding does not work and in some cases can cause the growth of black sooty mold.

Reprinted from "Reviewing Thrips Management" by Leanne Punt, University of Connecticut and Tina Smith, University of Massachusetts in a February 27, 2009 post on the New England Greenhouse Update website

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