Now that the warm weather is finally upon us, it’s time to start worrying about thrips control.
What we’ve learned over the years is that pesticides just don’t cut it – the only reliable chemical for western flower thrips in Ontario is DDVP, which requires constant application. This means biological control is your best bet. Here’s a summary of the most effective tools, tricks, and timing, to ensure your biocontrol dollars are well spent.
When temperatures are consistently above 24 C, thrips populations can escalate VERY quickly because of their shortened life cycle. We also know that large numbers of thrips can come in on chrysanthemum cuttings 1 this time of year.
For these reasons, prophylactic biocontrol strategies should be started NOW, so the thrips can’t pull ahead. As a rule, biocontrol programs are most effective if implemented when pest populations are initially low.
It may be a cliche, but an ounce of prevention really is worth a pound of cure, when it comes to thrips.
Ultimately, successful thrips biocontrol results from combining multiple tools so that no thrips life stage is left uncontrolled. This means applying bios to the foliage, to target adult and larval thrips, as well as applying bios to the potting mix, to target pupal stages.
Key players include:
- Predatory mites: Amblyseius swirskii or Neoseiulus cucumeris are the most commonly used. Weekly broadcasting can be used on the misting bench (or if pots are touching). Slow-release sachets are a better choice than breeder piles for long-term control out in the crop (for more info, click here). One mini-sachet per pot is often needed for effective control in large pots like mums, since mites don’t move well across benches2.
- Nematodes: most research shows that nematodes do a better job of controlling thrips pupae in the soil than adults or nymphs on leaves 3. Therefore, nematodes are best used initially as a drench, then as a weekly “sprench”, in the early stage of plant growth. When foliage is sparser, sprays more easily penetrate the canopy to reach the soil; sprays should stop when the canopy closes.
- Entomopathogenic Fungi (EPFs): Fungal-based products like BotaniGard, BioCeres and Met52 won’t provide control on their own (they need high rates of humidity for >25h to be a stand-alone product), but there are an excellent part of a biocontrol program 4 . A study just published by Cornell University demonstrated that Beauveria and Metarhizium-based fungal products are equally effective at controlling thrips in an ornamental crop 4. Spray once per week for at least 3 weeks.
- Think about dipping: with imported mum cuttings being a known source of thrips, it makes sense to decimate these thrips populations as soon as they come in the door. One way to do this is to dip cuttings in the dip rate of Landscape Oil (not the spray rate!!!). At this lowered rate, the oil is safe for cutting material but still smothers thrips. Use of other products (such as BotaniGard and insecticidal soaps) have also been investigated as dips for cuttings (click here for more info); label expansions are currently are being pursued in Canada.
- Switching to Swirskii: Though Swirskii are 2-3x more expensive than Cucumeris, they seem to be worth the cost in summer. Being from a warmer climate, research has shown they provide better thrips control than Cucumeris when average temperatures are above 25C 5.
- Mass trapping using sticky tape or large sticky boards can catch large numbers of thrips. These are most useful in crops where thrips are the main problem and only non-flying biocontrol agents are typically used. They can also just be used in “hot spots”. I’m currently testing different colors and patterns of sticky tape in commercial mum operations to see which gives the most thrips control. I’ll update you in the fall!
- Spray to “glisten”: Spray fungal-based products to wet the leaves , but not to the point of run-off. Spraying to run-off can actually reduce the amount of active product that remains on the leaf.
By initiating a bio program BEFORE temperatures rise, and using a combination of biocontrol agents and strategies like mass trapping, I promise you, control of thrips without pesticides IS possible. Fore more detailed information on successful thrips biocontrol, I highly encourage you to check out http://greenhouseipm.org/pest/thrips/ . (Note: we’ve sped up the site! For those of you who visited before, and found it too painful to use, I encourage you to try it again!).