Gardening jargon buster: biological control

Biological control: why birds beat bug sprays

“Biological control” is one of those gardening phrases that sounds really off-putting and overly-scientific for something that’s actually nice and cuddly and environmentally friendly and green and, frankly, just the kind of thing I am all about when it comes to gardening.

(It’s also, quite arguably, a lazy way of gardening, which gets my vote every time.)

For, biological control simply means that rather than using chemicals to kill any pests in your garden (eg bug sprays, slug pellets or any other sort of poison that can be employed to wipe out little critters that are harming your plants) you arrange for the pests to fall foul to a predator instead.

In one of the simplest examples of biological control, rather than killing slugs with slug pellets (that poison the slugs along with any other animals who might happen to eat them), you can just encourage birds and frogs into your garden so they eat the slugs instead.

Everyone’s a winner, right?!

Well, except the slugs, who are being taken out either way.

Frog | Wolves in London
Ribbit, ribbit, I’m just about to hop off and eat hundreds of slugs…

Encouraging natural predators is the most straightforward version of biological control (and the one I like the best).

You can use it to control pests such as slugs (which are eaten by frogs, hedgehogs or birds) or caterpillars (eaten by birds).

Controlling pests with biological control

Basically, create an environment that is pleasing to your chosen predator (a pond for frogs, for example) and wait for them to move in and start munching on their favourite foods.

A similar principle applies for other pests such as aphids, which are a tasty treat for ladybirds. It’s slightly harder to encourage ladybirds to arrive (despite those lovely wooden ladybird houses you see for sale) – so in this instance, you could actually buy some ladybirds and bring them into your garden. I kid you not, pet ladybirds are available to buy. Even better, you can buy them online.

Websites like GreenGardener (my personal fave) sell ladybirds and ladybird larvae. You order them online, wait for them to arrive by post and then release them onto the plants in the evening time, so that they don’t fly away but make a home for the night and then, with a bit of luck, have a good breakfast in the morning once they’ve got over their jet lag.

Apart from the normal kinds of predators, that you might expect to see in your garden anyway, you can also find a huge range of weird and wonderful things that are all ready to wipe out your pest problem. I have to confess, at this end of the scale, biological control is, perhaps, as odd and scientific as the name implies.

One of the more popular are nematodes, micro-organisms that live in the soil. Different types of these eat different things. Though, I use the word “eat” rather loosely, since what they really do is enter the body of the prey and destroy it from the inside out. Charming.

You can get nematodes to control a range of pests, from slugs to vine weevils. For all of them, it’s important to apply them to the soil in the right conditions (which includes both water levels and temperature) in order for them to be effective.

Then there are parasitic wasps that feed on whitefly, predatory mites for the red-spotted spider mite, midges and lacewing larvae for aphids (along with ladybirds)… …plus various others, I’m sure, that I’ve not heard of yet.

Does it work?

Does this all sound too good to be true? Well, in all honesty, that’s because it is.

The problem with biological control is that it’s not as effective as a pesticide at destroying the problem for you. Where a bug spray will probably kill every single last bug on your plant (and likely lots of bugs around your plant and other perfectly nice bugs that weren’t causing problems on your plant in the first place and perhaps a few passing honeybees too), biological controls will most likely only help to keep the problem in check. The poor old ladybird can’t eat all the aphids. And, in fact, if the predators did eat every single last one of the pests, well, they would then die out themselves as they’d have nothing to feed on. This is particularly true for pests in greenhouses.

But, my lovely gardening friends, my mantra for this (if not always in life) is moderation in all things.

Yes, there may be some pests left in your garden and, yes, you might sacrifice a few plants to them, or nibbled edges of leaves, or maybe even, shock, the odd vegetable or two. But surely, surely, it’s worth it to grow in a nice biodiverse environment, where the food chain works as it should and you know you’re not responsible for killing the lovely honeymaking bees?

And so, in summary, biological control: not the best way of eradicating pests, but definitely the nicest. And besides, who wouldn’t want a bunch of ladybirds being posted through their letterbox?

Have you tried any of these yourself? I’d love to know how you’ve got on with them, do leave me a comment and share any tips or hints.

Myself, I have a pond with some frogs that don’t seem terribly keen on eating slugs, but perhaps eat a few. I tried releasing ladybird larvae last year, and found that the ones in the greenhouse were very happy and stayed a long time, plus another little colony that set up on one of my rose bushes, but there were some plants they obviously left straight away, where the aphids remained. And I used nematodes for slugs a few years back and they certainly worked, but I am slightly unsure whether I’m okay with the side effects of lots of snails dying too…

This is the third in my garden jargon buster series. Every fortnight I work my way through the alphabet chatting about a gardening expression. Come back in two weeks to hear all about calcifuges, or check out the rest of the series here: Gardening jargon buster.

PS, I have to just point out, I didn’t take that lovely photo of the robin up at the top of the post. It’s from a free stock photo website, free images, here: robin in snow.

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5 thoughts on “Gardening jargon buster: biological control

  1. I love this series so much! also I want some ladybird posted through my door. I am going to make you very jealous right now but we don’t have slugs here in DC. We have mosquitos but not slugs. The plants are safe the humans are not. I was going to introduce a chicken to munch them all up but i don’t think it is going to be very effective on my postage stamp of a lawn. Oh also we have red cardinals that live near by which are the best bird in the whole wide world.

    1. Hmmm, slugs or mosquitoes? You know, I think I would rather have slugs. Is that selfish?! But I really hate being bitten. And (as you might recall from our Thailand trip) the mozzies really love me…

      Glad you’re enjoying the series, my love, thanks so much! xx

  2. I much prefer the idea of going to war in this way rather in the bug spray way… Wouldn’t it be nice if we could put up one sacrificial plant and direct all the nasties to that one (or maybe it would take a couple…)

  3. This is a wonderful post! I have always gardened organically and love your ideas for natural pest control. I’ve just started an allotment and have been considering nematodes…also love the idea of mail order ladybirds! 🙂 Laura x

  4. A really interesting post. I’ve not tried nematodes but I hear they’re quite effective. I’ve got frogs too, I like to imagine them creeping out at dusk and eating their body weight in small slugs. CJ xx

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