Will van Vliet of Van Vliet Greenhouse operated as a gerbera daisy cut flower grower a few years ago, who struggled a lot with biocontrol in his greenhouses. Whitefly and thrips were specifically what hindered his operations the most at the time. "Growers need to understand the full dynamics of biocontrol and how it operates in the entire system," he says. "We cannot just apply agents ad hoc. We need to know how they affect the life cycles of the pests they are trying to target." Will recalls a conversation with Ronald Valentin, an IPM specialist, early in their professional relationship. "When we met, maybe 15 years ago, he drew the lifecycle of thrips on a whiteboard in my warehouse. He explained where different biocontrol agents work on thrips—some targeting larvae, others focusing on adults. In so helping me to understand the dynamics of BCA's, my problems with these pests were finally solved."
First, there needs to be a pitchfork approach to biocontrol
The use of multiple biocontrol agents within one system makes BCA's as a concept more reliable. This multi-pronged approach, which Ronald refers to as the "pitchfork approach," ensures a more robust and reliable system. "The more prongs you have on the pitchfork, the stronger the system becomes," he explains. "Many growers today are just handed a bottle of bugs—maybe Amblyseius cucumeris for thrips—and told to put it out, but they don't really understand what it does or where it fits into the pest's lifecycle."
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The added banker plant strategy
While many greenhouse growers purchase beneficial insects from producers and suppliers of biocontrol, Ronald emphasizes the importance of banker plants as a complementary strategy. "Banker plants have been a challenging mindset shift, especially for biological control producers," he admits. "In essence, putting banker plants in might reduce the need to introduce biological control agents. But at the same time, it makes the whole biological system a lot more reliable, which is what growers are looking for."
Banker plants serve as a habitat for beneficial insects, allowing them to establish and maintain populations within the greenhouse rather than only being introduced reactively. "The function of banker plants is really to create a system where you maintain a population in the greenhouse, even if you don't have pests in the crop yet," he explains. "You're working more proactively, whereas historically, pesticides have always been reactive—spray when you see a problem."
This proactive approach is critical to a successful IPM strategy. "My focus has always been using biological control agents (BCA's) as a first line of defense in everything you do," Ronald states. "If you deliberately start using pesticides with biologicals at the same time, it's a no-go. It doesn't work. If a grower says, 'For this pest, I'll use biologicals, but for this pest, I'll use pesticides,' it's a recipe for disastrous results."
Melissa McIean, another IPM specialist, echoes this sentiment, emphasizing the importance of fully committing to biological control strategies. "You have to think about your IPM program as if you don't have synthetic pesticides to fall back on," she says. "It's not that you should never, ever spray, but it should be an absolute last resort. It is option X,Y,Z, not option B,D,E. No matter what you spray, there are no truly compatible pesticides. They simply don't exist."
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The now and then of banker plants
The concept of banker plants originated in the late 1980s and early 1990s through the work of Dr. Pierre Ramakers, an entomologist at the Dutch Research Institute in Naaldwijk. "At the time, there were major challenges with aphids in greenhouse bell peppers," Ronald explains. It was the weak link in the biological control system—if aphid control failed, growers had to use pesticides that were not compatible with the other BCA's they were using, failing the overall biological control system."
Ramakers proposed introducing a plant, such as barley or oats, that would host an aphid species that only feeds on cereals. "That aphid is not a threat to your pepper crop," he says. "But it serves as a host for parasitoid wasps like Aphidius colemani, which in turn control the harmful aphid species attacking the pepper crops."
"By maintaining a consistent population of beneficial insects, growers can respond more effectively to pest pressures without the disruptive cycle of spraying and reintroducing biologicals," Melissa adds.
The shift toward biocontrol has been a long process, but growers and researchers continue to refine and expand these strategies. "It's a mindset change," Ronald says. "We need to stop thinking about biological control as a product you buy and instead see it as a system you cultivate."
For more information:
© Van Vliet GreenhousesVan Vliet Greenhouse
Will van Vliet
info@vanvlietgreenhouses.com
vanvlietgreenhouses.com