For over two years now, the American Floral Endowment (AFE) has been hosting monthly webinars in their Grow Pro Webinar Series. AFE invited Dr. Rose Buitenhuis, the director of biological crop protection at the Vineland Research & Innovation Centre (VRIC), to discuss how to control thrips through IPM.

Buitenhuis noted thrips have always been a problem in Canada, but became a bigger problem when Ontario started banning pesticides in 2009.

Ontario flower growers moved away from pesticide management practices and now are “mainly managing thrips biologically.” Considering these growers are spending about 70% of their biocontrol budget on managing thrips alone, they continue to search for practices that control other pests as well. Buitenhuis said Ontario has “pushed the industry towards using biological control for all pests.”

There are various IPM strategies that Buitenhuis recommended, starting with dipping any plant cuttings. Growers should assume that the thrips are there on the cuttings – “by dipping them, you get rid of most of them.”

Predatory mites can be incorporated during propagation, followed by mass trapping and sachets. At the end of the IPM program, if you’re still finding thrips, “you may have to use a final cleanup spray with a pesticide” as a last resort.

Every four years, the VRIC sends a survey to ornamental growers and greenhouse growers. Each survey, “thrips are always listed as the most challenging pest and also causing the most crop losses,” Buitenhuis reported.

The results from the 2022 survey showed over half of growers weren’t happy with their thrips IPM program and were experiencing more frequent and severe thrips outbreaks.

Based on these results, the VRIC started looking into the data to see what changed. While looking at the patterns of these thrips outbreaks, they noticed they became more frequent in the past 14 years.

The Ontario Ministry of Agriculture, Food & Rural Affairs (OMAFRA) conducted a study in 2016, identifying the thrips species found in greenhouse floriculture in Niagara, ON. The majority of the thrips found were the common Western flower thrips (WFT). However, one-third of the pests were identified onion thrips (OT), a species which is naturalized in Canada but stopped being predominant in the 1980s. This result was “unexpected but would explain these observations of outbreak,” Buitenhuis said.

Image courtesy of VRIC

The VRIC expanded upon the study, identifying thrips species on other greenhouse crops in Ontario: tomatoes, cucumbers, peppers, eggplants, strawberries and cannabis. Buitenhuis summarized that most of the thrips present were WFT, but in some of the crops, a large proportion were OT, especially in the tomatoes and cannabis.

The researchers also came across exotic thrips species in ornamental and tropical plants. These thrips were introduced through the global trade of plant materials, especially as consumers’ desire to grow tropical plants increased during the pandemic. As countries ban the use of hard pesticides, they are providing “more opportunities for thrips, and especially the resistant thrips, to make a bit of a comeback.”

Climate change may be a factor because if the temperature is warm enough, thrips don’t need to overwinter in their egg stage – just continue on their lifecycle.

Buitenhuis also pointed out that more exotic species are being found because of increased surveillance. Simply put, “if you start looking, you will always find something.”

Growers should take the time to identify thrips whenever they see “something that is out of the ordinary.” That can mean an IPM program that used to work isn’t working anymore, the damage done to the plants is different or there’s an outbreak in a plant species that’s never been infested before.

Although most of the thrips found will most likely be WFT or OT, Buitenhuis recommends “identifying from time to time so you don’t become complacent.”

There are many ways to identify thrips, and Ashley Summerfield and Sarah Jandricic from OMAFRA created a free guide for Canadian and northern U.S. growers. This guide includes thrips species commonly found in Ontario greenhouse crops, along with a few potential invasive species. Considering this guide was simplified for anyone to use, it should not be used as a conclusive identifier.

The color of the thrips alone cannot identify the species, as each species has a wide range of color variation. Color distinction is a common misconception; colors can change based on temperature, lighting, the age of the thrips and even the preservation method.

Some other identifications that can be used are the color of the ocelli spots on their heads, as well as the presence of hair on their heads and bodies.

The VRIC has been doing trials for about four years now and is getting closer to creating a complete IPM program focused on OT. They are working on new projects to study the biology and behavior of another threatening species, Thrips parvispinus.

Buitenhuis’s main takeaway was how controlling thrips requires a systematic approach. “Biocontrol isn’t the only strategy against thrips. You have to combine it with cultural practices and also choose resistant varieties… that all together will give you an effective thrips control,” she said.

by Kelsi Devolve