When Chris Schlegel started working at DS Cole, one of New Hampshire’s largest commercial greenhouses, the pest control strategy was simple: spray everything with insecticide as soon as the first signs of pest infestation appeared, and repeat weekly.
Chris Schlegel, chief agronomist at DS Cole, said biological control has replaced chemical pesticides as the first line of defense against pests.
This strategy was abandoned and replaced by a different approach. As part of this approach, Schlegel and her colleagues reduced the frequency and number of chemical control methods used, even when they were used. They no longer use pesticides, but instead primarily employ so-called “biological control,” which utilizes natural processes to combat pests.
In greenhouse agriculture, biological control is primarily achieved through the use of predatory insects, which are harmless to plants other than their prey. Many growers, such as DS Cole, use biological control to significantly reduce pesticide use.
Every new technology has its pioneers, but many New Hampshire farmers still rely on pesticides as their sole means of pest and disease control. Jonathan Eba, a field specialist at the University of New Hampshire Extension Center, and his colleagues, including Amber Venchesi-Wahl and Amy Papineau, are working to make the transition to biological control easier and more effective.
”While providing direct technical assistance to greenhouse growers across the state, I gradually realized they needed clear, step-by-step instructions,” said Eba, one of the team members assisting growers like D.S. Cole. “So I developed a biological control starter kit. It’s a program that can help people get started, and then they can tailor it to their specific needs in subsequent years.”
The biological control starter kit contains information on specific organisms that growers can use, as well as standardized application strategies for pest infestations. Eba’s approach requires growers to regularly monitor insect activity in the greenhouse—for example, using sticky yellow cards to catch flies moving between plants—and to determine the timing of predatory insect releases.
The use of chemical pesticides may still be necessary, although their frequency and dosage will be reduced.
”I don’t know anyone who grows ornamental plants without using pesticides,” Eba said, “but biological control significantly reduces the amount of pesticides used.”
In 2008, Schlegel began experimenting with biological control at DS Cole. He released mites that fed on thrips, which were damaging gerberas. These thrips developed resistance to chemical pesticides, and even weekly spraying failed to control them. The experiment was soon expanded to control whiteflies, which were damaging poinsettia crops. In subsequent years, DS Cole began growing herbs in pots, and the advent of edible plants made reducing pesticide use even more important.
Schlegel said biological control is currently the agency’s first line of defense against pests, and chemical control will only be used if there is an outbreak of pests and no commercially available natural enemies are available.
Schlegel stated that biological control has many advantages. First and foremost, it’s safer for the greenhouse’s 80 employees and the environment. Other benefits include the fact that many of the plants grown by DS Cole are purchased by other growers who don’t want pesticide-treated plants to interfere with their own biological control strategies. Finally, after reducing pesticide use, they began detecting native insects on yellow sticky traps. These spontaneously emerging insects, used in biological control, fly in through open windows, something they simply couldn’t have done in the era of widespread chemical pesticide use.
What about costs? Does DS Cole spend more on biological control than on traditional spraying methods? Schlegel believes there’s no need to calculate these figures.
Chris Schlegel, chief agronomist at DS Cole, said sticky yellow cards are placed throughout the greenhouse to monitor for unwanted insects.
”I think the most important thing for us and many other farmers is that, considering the environment, the safety of our employees, the bees, and so on, all these factors justify the effort,” Schlegel said. “This approach has been very successful. We still encounter pests, but we can control them more effectively. If you haven’t used a lot of chemicals before, pest control is much easier because the pests haven’t yet developed resistance.”
Schlegel stated that the extension department is a trusted partner for DS Cole in expanding the use of biological pest control methods. Integrated pest management experts assist the company in pest identification and control strategy development, and also organize monthly webinars and in-person pest management seminars. DS Cole has agreed to host one such seminar in October 2025.
”We got a lot of help from the University of New Hampshire, and they also collaborated with a lot of knowledgeable people,” Schlegel said.
”One of my goals is to get the word out that the amount of pesticides used on ornamental crops in New Hampshire has been reduced thanks to biological pest control,” Eba said.
If New Hampshire greenhouses can routinely use biological pest control methods instead of pesticides in the future, these businesses will be able to produce healthier produce, keep their employees safe, and potentially benefit the environment.
Post time: Mar-17-2026