Some growers are reporting infestations of western flower thrips where scouts are finding up to 400 thrips on sticky cards in a week. Despite spraying once or twice a week, thrips are still a problem in the greenhouse. A grower recently asked, “Why are these insecticides no longer effective for western flower thrips?” Unfortunately, some populations of thrips are becoming resistant to certain insecticides.
In March 2013, Michigan State University Extension surveyed growers, and four greenhouses reported that spinosad (Conserve) was no longer working for them while two greenhouses reported that abamectin (Avid) was not effective.
In 2013, MSU’s Dave Smitley and David Mota-Sanchez did insecticide bioassays of four active ingredients on populations of thrips from MSU research greenhouses and commercial greenhouses in Michigan. They found that populations of thrips from MSU were more highly resistant to spinosad (Conserve) and acetamiprid (Tristar) than the populations of thrips from commercial greenhouses. Other populations from commercial greenhouses were resistant to dinotefuran (Safari) and abamectin (Avid).
For this growing season, MSU Extension recommends the following products for thrips control:
Hachi-Hachi (do not use on impatiens or New Guinea impatiens)
Read the full MSU article on thrips control in the greenhouse.
Source: Michigan State University Extension