Organic Solutions to Chilli Thrips
"Everybody knows that pestilences have a way of recurring in the world, yet somehow we find it hard to believe in ones that crash down on our heads from a blue sky. There have been as many plagues as wars in history, yet always plagues and wars take people equally by surprise."
Albert Camus, The Plague (1947)
Death is lurking in my garden.
Once a place of simple vitality and easy joy, a pestilence has now come silently creeping. Stems have withered, blooms have browned and fallen, new leaves are curled, shrivelled and deformed. The desolation rests, heavy on my soul, like a thick, well-rotted mulch.
Alright alright, it’s not that bad. But my garden has bloody chilli thrips!!! They’ve suckered onto my sweet pea seedlings, turned them weak and wrinkled, they’ve damned near killed one of my favourite roses and I’m grumpy and determined to wallow! …Along with what seems to be the vast majority of gardeners in Perth.
Although chilli thrips were known to be living in North WA as far back as 20 years ago, they’ve only started venturing further south in the last few years. And this year in Perth they’ve been BAD. So bad that it seems whenever I walk into my local garden centre there’s a handful of people, brows furrowed, wielding sickly brown roses and waiting for diagnoses. And the diagnosis is always the same - chilli thrips (Scirtothrips dorsalis).
I must admit it has been interesting to watch this play out. There is still a general acceptance of pesticide use in our gardens. Most garden centres have at least a few shelves filled with sprays of varying degrees of intensity. Increasingly these sprays have names involving words like ‘eco’, ‘nature’ and ‘bio’, implying that the actions of the spray are uniformly beneficial to all living things in our gardens (except the critters they are designed to eradicate). For many years I bought this stuff too and sprayed it haphazardly on any plant that was looking lacklustre.
But in the last few years I have fundamentally changed my perspective on how to grow a healthy garden. And now that thrips are setting up lodgings in my rosebuds and sweet pea sprouts I have the perfect opportunity to proselytize endlessly gently share my views with all of you guys.
The thing is, nothing is actually ‘natural’ about even the most natural of these sprays. I say this irrespective of whether they contain insecticidal neurotoxins like imidacloprid, acetamiprid, spinetoram, or pyrethroids, or whether they are as simple as basic soaps, garlic and chilli sprays, or vegetable oils (like Neem oil).
Some of these products may describe themselves as ‘naturally’ or ‘organically’ derived. For instance pyrethroids are made from Pyrethrins found in Chrysanthemum flowers and Neem oil is a vegetable oil made from pressing the fruits and seeds of the neem tree. But my issue is not really with the ingredients anyway. No matter how ‘natural’ the spray, the act of instantly wiping out an entire group of insects in your garden is not natural. Generally speaking, in nature different species’ populations are kept in check because a balance is established between predator and prey. This means that the prey is just as integral to that balance as the predator.
In my view, the best thing you can do for the long-term health of your plants is to work to establish a diverse garden that has many different insect populations living in relative balance. There are several reasons why this is a much better solution than pesticides:
1. Over time, insects become resistant to pesticides.
This is because of a basic, immutable principle of evolution and natural selection. When you use a pesticide (unless you kill 100% of the insects you are aiming to eradicate) usually a few of the ‘pests’ will remain. These few will be those insects that were naturally least susceptible to the pesticide. When they then reproduce, they will pass on their natural resilience to their offspring, making their offspring more immune to the actions of the pesticide too. Over generations, this pattern leads to the evolution of species that are resistant to our pesticides (it’s the same process that is leading to wide-scale antibiotics resistance in humans and farm animals too).
If, instead, you encourage greater insect diversity in your garden, natural selection is allowed to play out in an entirely different way. Instead of fostering pesticide resistance, the ‘pests’ and the ‘beneficial insects’ that eat them, will engage in an evolutionary arms race; a continuous competitive struggle between predator and prey, whereby prey become better at avoiding predation, and predators become better at capturing prey.
Imagine if a pesticide was on the market that adapted to your specific garden environment and changed flexibly over time to optimise its ability to destroy your ‘pests’. That’s the kind of thing that living organisms do, not sprays. Growing a diverse garden, full of herbaceous, flowering plants is a fantastic step towards creating a diverse garden ecosystem that allows all insects (even ‘pests’) to co-exist in a healthy balance. More on how to do that in a minute.
2. Most pesticides are a blunt weapon that won’t only harm the bugs you’re aiming at.
At first glance, this can seem like a good thing. For instance articles touting the benefits of neem oil happily proclaim that it ‘kills over 200 species of insects, not just a few’. The problem here is that our system of categorising insects is binary - they are either good, beneficial insects, or bad ‘pests’. In reality, all of these insects are contributing to our garden in various ways and they generally only become a problem when one population balloons out of proportion all of a sudden.
What’s more, many pesticides will claim that they don’t harm ‘beneficial insects’ like predatory wasps, bees, spiders, ladybugs and butterflies (as long as they aren’t sprayed directly on them or their larvae). But the spray itself has no ability to differentiate between the bugs we like and those we don’t, it just works by smothering those of them that are soft-bodied (like caterpillars, aphids and scale). And, like many chemicals used in industries, our methods for classifying ‘harmful’ and ‘non-harmful’ are imperfect and non-absolute. Below is a quote from a fact sheet for wine growers made by the University of Melbourne, looking at the impact of pesticides on beneficial insect species in vineyards. The author explains what the toxicity ratings of various pesticides actually reflect:
The toxicity ratings for individual chemicals are derived from laboratory and semi-field-based tests in accordance with the guidelines of the International Organization for Biological and Integrated Control (IOBC) Working Group on Pesticides and Beneficial Organisms. Toxicity ratings indicate the reduction in the ability of the beneficial species tested to provide pest control, and range from:
1. The chemical is ‘harmless’ and kills fewer than 25% of the beneficial species of interest.
2. The chemical is ‘slightly harmful’ and kills between 25% and 50% of the beneficial species of interest.
3. The chemical is ‘moderately harmful’ and kills between 50% and 75% of the beneficial species of interest.
4. The chemical is ‘harmful’ and kills more than 75% of the beneficial species of interest.
As you can see, even the chemicals deemed ‘harmless’ may kill a non-zero percentage (up to 25%) of beneficial insects, and if you click through the link to look at the toxicity of the various chemicals examined, you’ll see lots that have ratings of 2 and 3, indicating that they kill 50% or more of the beneficial insects examined.
3. You’re taking away something’s food source.
Even in the best case scenario where no unintended insects are harmed, using these sprays to wipe out a whole group of bugs has one unavoidable consequence: you’ve instantly eliminated a food source for other insects in the garden. Generally, ‘beneficial insects’ like ladybirds, lacewings, wasps (and many others) reproduce more slowly than insects like aphids and scale. This is a shame, because it means there’s usually a delay in between the aphids appearing and their natural predators; ladybirds, arriving to clear up the mess. It’s during that window that many people get stressed out about their plants and resort to sprays. If we just grit our teeth and wait, 9 times out of 10 our garden ecosystems will solve the problem for us - and in a much more long-lasting way.
It’s probably pretty obvious by now that in my quest to save our gardens from Thrips I am not going to be offering up any pesticide-based solutions. Instead, I want to share exactly what I am doing to address the thrips in my garden in the hope we all might arrive at a few long-term, pesticide-free solutions that outlast this current wave of tiny, pestilential garden bandits and let our gardens flourish in the most natural and ecologically diverse way possible. Read on to find out how!
What are Thrips, anyway?
Thrips are a large group of very small insects that feed by puncturing plants and sucking the sap out of them. Some thrips are predatory (some actually eat other thrips), but generally they tend to be disliked by gardeners because their sap sucking literally drains the life out of the plants they attack, leading to a garden that gets progressively sadder and wilt-ier. Despite there being over 6000 species of Thrips, if you are in Perth it is likely that any recent garden damage is due to Chilli Thrips, a specific kind of Thrips that has recently taken the opportunity to flourish in Perth due to variations in humidity and temperature that I must admit I hadn’t even noticed.
But my garden has definitely noticed. Have a look at these photos of the same rose bush taken a few years apart; pre- and post- the arrival of Thrips.
Oh my GOD!! It’s even worse now I’ve actually lined up all the photos and stepped back to look at them! Isn’t that HEARTBREAKING!! Blimey. Ok but it’s ok. It will all be ok. I may be sad and stressed BUT I have a plan and it is multilayered and I think this can all be fixed!
Do you have Thrips?
Before we talk about what to do if you have a Thrips problem, it’s worth making sure you actually DO have Thrips in the first place. So what do you look for?
First, take a look at where the damage is occurring. Thrips tend to preferentially attack certain species of plants. So despite my big whinge at the beginning of this article my garden is in fact not remotely decimated, dead or brown. Happily, 99% of my plants remain entirely unaffected by the Thrips plague, which has only really settled on my roses, chillies and sweet peas so far (if you need another argument for growing a diverse range of plants in your garden, this is it: grow a wide number of plants and your garden will always look green, even if a few things aren’t faring so well). If you’re in Perth and your roses are sickly, chances are high that Chilli Thrips are to blame.
There are some characteristic features of Thrips damage, although these do vary from plant to plant. In roses, look for brown, bruised flower buds, withered, brown shoots, wrinkled leaves and general defoliation (loss of leaves) as the Thrips take over. I am not actually certain that thrips are in my sweet peas, but there is a general curling of new shoots, slowed growth and they just look…crappy in a way they never have before. To check out some more photos of Thrips infestations in roses, look here.
At any rate, one of the benefits of using gentler methods of ‘pest’ control is that you don’t actually have to be 100% certain what bug is doing the damage. All of the methods I’m about to recommend adhere to the ‘first, do no harm’ principle, so if it turns out Thrips are damaging my roses but not my sweet peas, I won’t have unnecessarily doused my sweet peas in anything weird, and I can then try to work out what else might be going on. That said, I’m pretty bloody sure it’s Thrips.
What to do about Thrips:
So ya garden has Thrips. Bugger. I feel your pain. Now, what do you do?
Step 1. Make the most of the current change of temperature and take action now (in Autumn)!
Thrips are most active in spring, summer AND autumn (so, errr basically all the time). Except thankfully they are significantly less active during winter. As the weather cools Thrips are slower to reproduce and can often go dormant in our garden soil in June/July. This gives our plants a brief reprieve until spring (when thrips hatch once more and go to town on our rosebuds). The good news is that if we take action NOW, we can make the most of this temporary lull in their reproduction and get ahead of the little buggers. Here’s what I’m going to be doing in the next few weeks:
Step 2. Mulch thickly before spring
If thrips are going to be setting up camp over winter in the soil beneath our infested plants, one thing we can do to limit their reproduction success is to add a thick layer of mulch to our garden beds. If added thickly, this layer can limit their ability to hatch out and re-infect our plants in spring. It won’t eradicate them entirely, but it will contribute to slowing the spread (this is beginning to sound like a COVID article!)
Step 3. Prune - heavily! Or chuck out.
Thrips live in the stems and flower buds of the plants they infest. For plants like roses (which can tolerate pretty harsh pruning) one solution is to prune away the parts of the plant that have obvious signs of infestation. Bag the infested bits of plant and throw them away (don’t compost them or you’ll be giving yourself an even bigger mess come springtime when your thrip-infested compost is spread through the whole garden!).
For plants that don’t respond to heavy pruning (like sweet peas), you have two options: either throw the plant out and start fresh once you’ve made a dent in the thrips population, or encourage beneficial insects to the site of affected plants in the hopes that they’ll eradicate the thrips for you. ‘How do I do that?’ you ask? One great first step is through clever companion planting….
Step 4. Use companion planting to attract thrips predators
This option requires a little bit of reverse engineering (which, incidentally is a really good process to go through any time you have an issue with a particular insect). First, work out what insects (or other animals) prey on the insect you seek to control. Natural predators of Thrips include: Neoseiulus cucumeris, Stratiolaelaps scimitus and Typhlodromips montdorensis (these are all species of small predatory mites that eat Thrips larvae), Minute Pirate Bugs (Orius insidiosus) which are larger bugs that eat both adult Thrips and larvae. Other common garden insects that like to eat thrips include lacewings and ladybirds. Next, work out how to attract these insects to your own garden and keep them there.
The first rule for attracting any beneficial predatory insects to your garden is to aim for as much plant diversity as possible. This provides them with a plentiful buffet of food all year round. Flowering and nectar-rich plants are ideal.
To attract ladybirds (which feed on pollen as well as thrips), plant pollen-rich plants like fennel, dill, coriander, cosmos, alyssum, caraway, marigold, yarrow, chives and scented pelargoniums. One important thing to keep in mind is that in order to get the pollen you have to allow all of these plants to flower. This means letting your coriander and dill ‘bolt’ (i.e., flower) which is actually always a fantastic idea - the flowers are beautiful, it’s fantastic for insect diversity, once the flowers finish you can collect seeds to eat or grow again next year and little coriander, dill and fennel blossoms look amazing tossed on top of a salad, quiche or cake!
To attract lacewings (which like both pollen and nectar) plant pollen-rich and nectar-rich plants, including calendula, marigolds, ornamental chamomile, Marguerite daisies (and other daisies) and the flowers produced by alliums like onions, spring onions, chives and garlic (once again, you have to let these plants go to seed to enjoy the benefits of their flowers). If I hadn’t already convinced you to ditch the pesticides, bear in mind that lacewings are one of the beneficial insects that actually are harmed by pesticides, so if you want to have a garden filled with these lovely, delicate insects, hands off the sprays!
Step 5. Buy some new pets
By now it should be clear that one of the best long term solutions to bug problems in your garden is…MORE BUGS! But this process - admittedly - does take time and if your plants are currently under a thrips siege, you can’t be blamed for wanting to speed things up a little. Fortunately, you can! There are several websites online now that allow you to order little test tubes filled with the larvae of specific kinds of beneficial insects. The one that I use is Bugs for Bugs (not a paid promotion or anything, I just think they’re great!). Just last week I ordered several thousand minute pirate bug larvae to be delivered in a fortnight’s time, so STAY TUNED.
Once these bugs are released it can still take a little while to notice any improvements in your own garden (natural processes take time), and it is even more important to make sure you are growing enough flowering plants to support your new population of beneficial bugs. But the great thing is that if you provide these critters with enough natural food sources, they’ll stick around and will hopefully produce a stable population that can take care of your plants for you year after year!
Final suggestions
If you’re not quite ready to buy 2000+ new pets for your garden, one last thing you can try to eliminate your thrips (in addition to the other suggestions) is to give them a heavy spray with a hose to blast the thrips eggs off or to use a vacuum to try and suck the thrips larvae directly off the plants themselves. Admittedly I have not given this a go yet (part of me is now willing to let the thrips happily procreate in the hope that they’ll provide an even bigger feast for my minute pirate bugs!), but I have found several pest-control websites offering a similar service. A hands free vacuum run along the underside of the leaves is purported to remove many of the thrips eggs. I say if you’re feeling lucky and you have a vacuum cleaner that can make the journey outside, give it a go!
Ok! That’s all from me for this week! I hope I’ve helped you find some pesticide-free solutions for dealing with the occasional plague of less-that-welcome critters in your garden. Until next time,
Happy gardening!
Xx Casey