Plant Doctor Archive

Bugs on my veggies

I have green vegetable bugs and spider mites on my beans. How can I control them?

Green vegetable bugs will suck the living daylights out of your leaves and developing beans, causing them to shrivel up. How do we control this bug? In order to know that, it is good to know its life cycle.

If we start to look at the life cycle, we might as well start at the top with the eggs.

The eggs are laid in batches of a couple of dozen. If you look carefully, you'll see they're hexagonal in shape.

They've got a flip-top head, and out come the first tiny wee grubs.

The grubs that come out of the egg are almost totally black. They're very small, but they'll soon grow, shed their skin and show a few white dots on their body.  

Then they shed their skin again and become even bigger, showing some yellow spots on the body.

After a few moults, they slowly become greener and greener, with red patches, black patches and white patches.

When they shed their skin a few more times, they arrive at the adult stage — the green vegetable bug with wings, just as we know it.

How do we control them? First of all, you can throw any insecticide at them and it will kill them. If you want to go organic, you could use pyrethrum, but here is my trick — a really clever one.

Use their smell. If you squash one of those bugs, it emits this pungent odour which not only wards off predators, but also warns the others in the plant there is a predator at large.

What all the other green vegetable bugs do, is they drop down to the ground and play possum, and think, 'I hope he doesn't see me.'

When you see them all drop on to the ground, you squash them as well, making more smell, making more green vegetable bugs drop off, and basically in no time you've got about 85% of the whole population squashed on the ground.  

The next bean pest is certainly not as messy. It's the two-spotted spider mite. You can always tell a leaf damaged by a two-spotted spider mite. Just look at it — totally white-spotted, stippled, and blotched. If you turn it over you can see a lot of webbing, especially if you've got good eyesight or a hand lens.

On that webbing walk minute little two-spotted spider mites. They scrape the surface of the cells on the leaf's underside and suck out the juices, causing the spotting.

Spider mites have got one little weakness — they hate cold, wet feet. They love the warmth. Here's a tip. If you want to control spider mite or stop them from establishing on your leaves, mist them on the underside with water every other night or so, making the environment damp and cold, and the spider mites really hate that.  

Of course, you can use miticides and things like that, but I don't go for that.

But, hey, I've got some good news for us gardeners. For a while now a company called Zonda, in Hawke's Bay, are selling predatory mites that feed on the spider mites. They send them out in packets. What you get are packets of bean leaves with the same mite damage on it, but full of predators.

You literally hang these leaves onto your plants. You can attach them with a paper clip. What happens is the predators will go out hunting for their prey and feed on your pests. Simple as that. You let the predators do the work.

Where can you get them? From Zonda, Switched on Gardener, Veg Gro, Fruitfed, and even Parva Plants.

Ruud Kleinpaste

Advice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

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