Running on the resistance treadmill

Running on the resistance treadmill

2019 Focus on Pest Control - Resistance Management

Through different research projects, Dr. David Smitley aims to help growers better deal with various pest problems.

December 27, 2018

Chemical products typically have a five-to-10-year shelf life before a pest species adapts and growers need to find another product to protect their crops, Smitley says.
Photo courtesy of Dr. David Smitley

Dr. David Smitley, a professor in the Department of Entomology at Michigan State University, spends much of his time researching pesticide and pollinator best management practices for the greenhouse and nursery industries.

Each year, he publishes a short guide for growers that breaks down the best products for growers to use to confront different pest problems. The 2018 version is available here; he says the 2019 update will be available in the first part of the year. Smitley is also working on a more comprehensive project with other researchers, called the IR-4 Project.

Two components provide the basis for the products listed in Smitley’s individual report, he says. “The first is the testing I do. A lot of that is the industry coming to me with a new product that they want tested. I also go back to the arthropod management tests and see all the tests on a given pest — say, green peach aphid. There might be only one or two reports on green peach aphid in the greenhouse, but several on some vegetable crops [grown outdoors]. That still gives me an idea of how well the active ingredient [in a product] works on green peach aphid.”

Smitley says that the list includes the products that will work best on each pest, but also advises growers to still take the time to determine which products are the best fit for their greenhouse. He also says growers should use yellow sticky cards and swap them out each week to evaluate products and their effectiveness.

Dr. David Smitley
Photo courtesy of Dr. David Smitley

Major resistance

Among the products currently available on the market, Smitley says one group is completely removed from his list because the products are ineffective on most greenhouse pests.

“Synthetic pyrethroids make up about one-fourth of the insecticides available,” he says. “What’s happened is that the insects in the greenhouse industry have developed a high level of resistance to that entire group and they don’t work on hardly anything in the greenhouse anymore.” Smitley adds that some growers are still using synthetic pyrethroids — sometimes known as SPs — and that the products can be useful in combating insects that fly into the greenhouse and interact with the product for the first time.

Smitley says the greenhouse industry has the most resistant insects of any agricultural crop because they are isolated populations contained within the greenhouse and are sprayed repeatedly. He says that, typically, a product has a five to 10-year shelf life before a species adapts to it and becomes resistant.

“Let’s take western flower thrips, for example, because it’s maybe the most important pest in the greenhouse,” Smitley says. “They are resistant to almost every group of chemicals that we have. So, when a new chemistry comes out — Pylon is an example of that right now — it works very well. It’s a new chemistry; [the thrips] have never been exposed to that insecticide before. But what we typically see is that, in five to 10 years, a resistance [has] been developed and we have to move on to something new. It’s a constant treadmill we are on combating these pests.”

In addition to identifying the best pest-fighting products, Smitley is researching pollinators and the best annuals and perennials for them.
Photo courtesy of Dr. David Smitley

New research in 2019

Smitley is working with several other professors — including Dr. Cristi Palmer from Rutgers University, James Bethke from UC Davis and Dr. Juang-Horng Chong from Clemson University — to develop a comprehensive guide of the best products to combat different pests. The IR-4 Project, has been funded for the past three years by a Specialty Crop Research Imitative (SCRI) grant, is nearing its completion and will be available during the first part of 2019. It will be available to growers for free at

“In the past, this has been informal,” Smitley says. “It’s been incomplete work.”

He adds that the SCRI grant is funding research into the best annuals and perennials for pollinators and the systemic effect of different products on pollinators too. But the proposal specifically called out determining the best products for growers to use. He also notes that funding through the Farm Bill — like the SCRI grant, a program that received increased funding in the new Farm Bill that both the Senate and House of Representatives passed in December; President Donald Trump has yet to sign the bill into law at press time — allows funding for more flexibility for researchers to pursue different topics. With the grant, he says, it’s unlikely that this research would be possible.

The difference between Smitley’s individual report and the forthcoming research is the amount of detail. Whereas Smitley’s report compresses his recommendations down to two pages, the research will have around six pages dedicated to treatments for each individual pest. For example, if a grower is having an issue controlling western flower thrips, he or she will be able to view a section devoted entirely to western flower trips and the different products on the market that could help the problem.

“We are going through all of the normal processes, reviewing [the work] for each other and then adding anything new that we know or have learned,” Smitley says. “It will be a lot more extensive than my two-page sheet. Just for whiteflies, you might have a six-page document that includes details on how well product works, not only if it works.”

The goal of the research project is the same as his two-page report: to help growers combat what can feel like a never-ending cycle of pest problems.