Thorsen’s Greenhouse, Delaware, Ohio

2017 Greenhouse Greats - 2017 Greenhouse Greats: Biological Controls

January 5, 2017

Thorsen's biologicals come in packets and naturally release into the crops.
Photo courtesy of Marilyn Norman
Marilyn Norman
Photo courtesy of Marilyn Norman


Thorsen’s Greenhouse has successfully finished an entire poinsettia growing season using solely biological pest control. And with 50,000 square feet dedicated to this holiday plant production, that’s no small feat. It was made possible through a three-part regimen of biologicals (the “good bugs”) released during the cutting stage all the way through finishing, which suppressed and/or eradicated fungus gnats and whiteflies.


Assistant grower Marilyn Norman was inspired to implement a biological control program after attending a grower seminar at Four Star Greenhouses in Michigan in 2015. After conducting some independent research, she checked in with suppliers at AmericanHort’s Cultivate event that year, and tried it out for the first time with their poinsettias. While Thorsen’s is no stranger to biologicals (they use them for thrips on several other crops), they hadn’t relied solely on a biological regimen all the way through a production cycle. The first year, they learned a few valuable lessons, including the need to purchase higher-grade sticky cards to keep an extra eye out for pests. “[I learned] what to look for and to really pay attention to certain areas, hot spots, where [pests] can pop up, and [also] how to place the biologicals,” Norman says.


As the poinsettias began to root, Norman sprayed nematodes within a preventative fungicide drench, which took care of fungus gnat issues at the beginning of the 2016 season. Amblyseius swirskii mites were distributed using an AirBug gun to combat early stages of whiteflies, then a combination of wasps on tiny packet cards — Eretmocerus eremicus and Encarsia formosa — were placed on stakes in the middle of the crop and released on their own. And after all that effort, “We finished completely spray free,” she says.