Thrips are active in many greenhouses now. If you use pesticides to manage thrips then plan to treat in the early evening. Thrips have two mass flights per day, so sprays in the early evening may contact more thrips. Treating before you see a peak in adult numbers on yellow sticky cards is 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. Small droplets of pesticide sprays are most effective for coverage.
To manage thrips, make two to three pesticide applications about 5 days apart and rotate pesticides with different modes of action. Two materials that some growers are successfully using are pyridalyl (Overture) and chlorfenapyr (Pylon). It appears that pyridalyl (Overture) is more toxic to second instar nymphs than adults. Also, Overture takes at least seven days to kill a majority of WFT, so don’t expect an immediate reduction in populations when using this insecticide. Read the label for plant safety. Both products have precautions.
Both of these products also have translaminar activity. Remember that translaminar insecticides penetrate leaf tissues and form a reservoir of active ingredient within the leaf, providing residual activity. Insecticides with contact or translaminar activity are generally better than pesticides that are systemic because systemic insecticides typically don’t move into flower parts (petals and sepals) where WFT adults normally feed.
Azadirachtin (Molt X, Aza-Direct, Azatin, Ornazin, Neemix) is an insect growth regulator (IGR) and “stressor” so may be helpful in some tank mixes. For example, if thrips populations are low and plants are not yet in flower, Beauveria bassiana (Botanigard, Mycotrol) and azadirachtin may be an option. Abamectin (Avid) (translaminar activity) with azadirachtin has also been working well for some growers.
Pesticide rotation options for management suggested by Dr. Raymond Cloyd, Kansas State University are:
* Spinosad (Conserve), Chlorfenapyr (Pylon), Abamectin (Avid), Methiocarb (Mesurol)
* Novaluron (Pedestal), Pyridalyl (Overture), Chlorfenapyr (Pylon), Spinosad (Conserve)
* Beauveria bassiana (BotaniGard/Naturalis), Acephate (Orthene), Spinosad (Conserve)
* Abamectin (Avid), Pyridalyl (Overture), Chlorfenapyr (Pylon), Spinosad (Conserve)
* Chlorpyrifos (DuraGuard), Novaluron (Pedestal), Abamectin (Avid), Bifenthrin (Talstar)
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, so it may be best early in the growing season. Pedestal is an insect growth regulator (IGR) labeled for immature stages. TriStar (acetamiprid – group 4A) or Aria (flonicamid – Group 9C) may also help suppress thrips.