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A look at rebounding pests

A Look at Rebounding Pests

March 8, 2018  By Gary Jones

Surely we’ve all heard the saying: “What goes around, comes around.” So, when looking into “what’s new” on the pest front, it came as no surprise to hear of some familiar old foes. One of my faculty colleagues here at Kwantlen (Kristine Schlamp) tells me that “broad mites seem to be the pest du jour.”

Following a recent meeting with several local biocontrol gurus, Kristine says this is “the third time I’ve heard this from pest people in the last six months.”

I first came across this pest about 25 years ago when it was responsible for devastating a number of cucumber crops in Yorkshire, U.K. It appeared from nowhere, casually threatened to be the next big pest, and then disappeared back into obscurity after a couple of seasons, hardly ever to be heard of again.


Until now, apparently, and in Canada.

One of the problems with this particular pest is that it is very hard to detect (they’re tiny), produces somewhat unusual symptoms that are easily confused with abiotic problems, and can be very difficult to control. But having them pop up as a “new” pest (again) begs the question: Where did they (just suddenly) come from? Maybe they got brought in. Maybe changes in control practices for other pests mean broad mites can now flourish. Maybe they’re there all the time and something just allowed them to become significant. Who knows. And maybe, they’ll disappear just as mysteriously as they came. By the way, if you ever want to see something in the natural world that seems slightly unfathomable, check out pictures of the females alongside the eggs they produce (size, shape) – it makes the mind boggle.

Mealybugs are another old-timer causing trouble again. While these are definitely not new, they never quite seem to really go away. They’re currently causing issues on many greenhouse ornamentals, in particular one of their favourite host plants; Phormium (New Zealand flax). While they have always been difficult to control, they now seem to be resistant to pretty much all approved insecticides, and depending on the time of year, many biocontrol options can be somewhat ineffective.

Talking of these old foes in the pest/disease arena, I’d love to know how much has been spent over the years on research to find ways of controlling Botrytis (grey mould) on greenhouse crops. You’d think we’d have that one cracked by now. But no, it’s a perennial problem that causes significant crop losses every growing season. Any grower worth thier salt knows the importance of start clean, stay clean, good greenhouse hygiene, proper pruning techniques, humidity control and other basic grower practices. So why is this still such a pain in the wallet?

Root mat in greenhouse tomatoes is another disorder that’s been around for a while but has made a resurgence as of late. It, too, seemed to be gone, only to resurface years later in a different country for whatever unknown reason. Just part of the new order of a truly global industry perhaps.

But enough of looking at old problems. What about the future? We have a number of new crop production systems. Aquaponics, converted shipping container systems and vertical farming methods to name but a few. I wonder what these will bring in terms of new commercially important pests/diseases, or old pests that exploit these new opportunities? And we also have new (commercial) crops, such as cannabis. Apart from mites and mildews, what new challenges will appear as we venture into these unchartered waters?

Researchers, plant breeders, biocontrol companies and pesticide manufacturers have consistently done a great job of helping growers keep up with controlling pest and disease organisms.

For example, if you didn’t catch it the first time around, check out the story of “Chili” the dog who is trained to find pepper weevil at Nature Fresh Farms (Greenhouse Canada, November issue and online here:

It seems that sometimes, when we look at what’s new in the field of pests and diseases, we don’t have to look too far and we don’t have to re-invent the wheel.

Gary Jones is Co-Chair of Horticulture at Kwantlen Polytechnic University in Langley, British Columbia. He sits on several industry committees and welcomes comments at

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