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This year I installed netting that was supposed to protect my plants from insects. However, what's happening is that although I've largely excluded pieris rapae, I'm getting largely uncontrolled aphid growth. The mesh is likely excluding lady birds, and possibly some predator wasps though I do see some aphids that have been parasitized. Snails, and wetas seem to be able to climb under the net.

I have found some lady birds sitting on the mesh trying to get in, and I've picked them off and put them inside.

If I go to a smaller mesh size to try and keep aphids out I think this will produce too much lowering of the light intensity, and ventilation.

And my Brussels sprouts are now over 6 feet tall pulling the mesh upwards creating gaps at the bottom indicating that small hoops with mesh don't work for them.

So, what's the best balance?

mesh mesh over hoops

  • what size holes / what gauge mesh are you using currently? – Nic Mar 20 '16 at 20:51
  • It's about 2 mm I think – Graham Chiu Mar 20 '16 at 20:53
  • I personally think this is one of those classic examples of nature having a balance and man making the problem worse rather than better. I think it's best that you just let nature in, and just plant enough to share with nature when she decides she wants some. – Escoce Mar 22 '16 at 13:26
  • The issue is I'm trying to grow plants that are not native to the region, and an being attacked by introduced non native pests. So there is nothing natural about any of this. – Graham Chiu Mar 22 '16 at 22:23
  • That's what we are all doing with our gardening. We all use introduced non native species irrespective of gardening or allotment vegetable growing. An individual female aphid will have up to I think 40 maturing young within her, to be born ready to go, a long with their own young in situ. A very fast growing population for sure. Remover the very fine netting, and replace with a netting that will exclude butterfly's and birds, but will easily allow the ladybirds in and out. If at the end of the growing season, let the birds loose to pick of any residual bugs. – user13638 Mar 25 '16 at 8:18
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Aphids can probably squeeze through even the finest mesh, Best to let in the predators, even buying some praying mantises could be worth it. They'll hopefully hang around until all the aphids are gone. I had a spider move into a potted citrus once which worked a treat. If you end up going sans mesh, just plant some sage between the plants to keep out the cabbage moth.

Not sure if white oil, even the milder version of 1 part dishwashing detergent to 4 parts vegetable oil can be used on brassicas. I read somewhere else that just soapy water might work so you could try that first, at least on the parts you don't plan on eating. Even if you test a plant or two then you'll know the outcome for next season.

I should also mention that the white oil would also need to be diluted in water but I'm unsure of the best concentration of either white oil to water or detergent to water for brassicas.

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