Up until this point, most of Ontario floriculture growers (and me!) assumed the only pest thrips we were dealing with was Western flower thrips (besides Echinothrips in a few crops like gerbera and poinsettia).
But a survey conducted in major commercial operations in 2016-2017, AND recent outbreaks of serious damage have proved us wrong. (You know what they say about assuming!). Keep reading to find out the truth about thrips!
Why Suspect Other Thrips?
When I first arrived back in Ontario in 2015, I heard a few consultants and growers in the area mention that thrips biocontrol programs didn’t seem to be working as well as they used to. More sudden and serious damage outbreaks were occurring, even at growers that had well-run IPM programs.
Step 1 in our investigation was to look at the quality of predatory mites (both Cucumeris and Swirski) in sachet-based thrips control programs, to see if that had changed. Besides a few mistakes that were easy for any grower to make (see this post), the quality of our bios is generally NOT the issue here.
So if it wasn’t the bios, could it be the pest that was different? When Echinothrips starting making it’s way on the scene, it certainly threw off a few IPM programs (and we are still figuring out how to better control it). Could another thrips be making a name for itself?
To investigate this, myself and a team of undergraduates collected thrips from 8 large commercial floriculture operations in Southern Ontario from May – August 2016, and repeated collections in 2 nearby operations in 2017.
The Survey Says!
Even I was surprised by what we found, and had subsamples of all our thrips sent off to a specialist in Ottawa to confirm our findings. (Shout out to Eric Maw!).
As you can see, over 30% of the thrips species in the floriculture greenhouses we sampled in Ontario were actually Onion thrips (Thrips tabaci)! This species looks VERY similar to Western flower thrips, and is impossible to differentiate with just a hand lens. We found them in many crops, but ratios were highest in Gerbera and Mums (both potted and cut). But we’ve recently been seeing outbreaks in other plant species as well.
We also saw that within greenhouses, the ratio of onion thrips can vary year to year. Check out Greehouse “A” in the figure below. in 2016 they have the going rate of around 20% Onion thrips in their crop. But in 2017 they had up to 66% onion thrips, and were seeing damage.
Why is Thrips Species Composition Important in YOUR GH?
Basically, it comes down to control. While we’re still unsure how effective the “usual” biocontrol tools are against Onion thrips, we’ve seen this pest overwhelm typical bio programs again and again. To avoid plant losses from this pest, chemical controls can be an effective option.
Let’s be clear: I am NOT recommending we all go back to spraying for thrips willy nilly. Not only will this NOT WORK, since it will just encourage pesticide-resistant Western flower thrips, but as an industry, we do not want to risk disrupting biocontrol programs for other pests, and getting back on the pesticide “wheel”. But, in cases where damage is appearing close to sale, or when thrips populations seem out of control despite good bio coverage, or on sensitive crops, spot sprays may be needed to reduce the number of Onion thrips overwhelming your plants. Post-spray, normal biocontrol programs for Western flower thrips can be resumed, depending on the pesticide residual.
How to Figure out Which Thrips YOU Have:
Normally insect species identification is better left in the hand of professionals. But given the changing situation in Ontario greenhouses, growers are going to have to know which species they’ve got in order to implement the right control measure. And going to a specialist every time you suspect it’s onion thrips means wasted time and more damage.
So, Ashley Summerfield (a Senior Technician at the Vineland Research and Innovation Centre) and I worked hard this summer to come up with a simplified guide to pest thrips for growers to use. (Hey, if my undergrads managed it, you can!).
Stayed tuned for Part 2 of this blog post on the best way to use this identification key, as well as more tips to determine if Onion thrips is your culprit. In the meantime, the key here or download this PDF: Key-to-important-thrips-pests-of-Ontario-greenhouses-2018