Thoughts on Blackfly and Runner Beans

At the moment we seem to have the worst infestation of blackfly on our beans that I can remember :(.

Our policy for the last 30 years has been not to use chemicals in the garden but I gave in and used some pyrethrum the other day (suposedly organic).

After using it I had some thoughts about whether I should have used a systemic (non-organic) insecticide.

Pyrethrum is a topical insecticide and kills on contact (doesn't seem to have worked very well) so it is a one time spray. It will, of course, kill any other insects on the plants like ladybirds, bees etc. We had no ladybirds and I used it when I couldn't see any bees around.

The problem is that if it hasn't worked very well I shall need to give more applications with the ensuing danger to other insects.

If I use a systemic insecticide (albeit non-organic) I assume it will only kill those insects feeding on the plants.

Here's my problem:-
ignoring the possible effect on humans on any possible residue of chemical in the beans, how will the chemical affect ladybirds, bees etc - if at all?

I would guess that ladybirds will only eat the live blackfly who will not have absorbed much of the chemical. Will this kill them?

Will the bees be adversely affected by the pollen from the flowers?

Without much in depth knowledge I am not able to make an informed choice.

I have too many plants (about 200) with much too much blackfly for me to remove them physically - as I generally do. Diluted washing up liquid is unlikely to have more effect than pyrethrum - and can't be used in a pressure sprayer.

Any ideas?

 

I'm in the same boat this year with a terrible infestation of blackfly. The dilute soap spray trick has not kept them at bay this year so eventually had a look in the garden shed and found some Provado - I don't like the idea of using insecticide especially a systemic like Provado but I was going away for a weeks holiday and didn't want to come back to find my plants all eaten. So I sprayed and it did the trick for a few weeks, the blackfly are creeping back again, I don't mind losing one or two plants so I'm holding off spraying for a second time.

Sorry I can't answer all your questions Shiney, I reckon anything that kills blackfly is not going to be good for their predators nor the bees - it advises spraying early in the morning or late evening presumably to avoid the bees. I can't tell if any bees have been affected by it - I doubt that Bayer (who make this chemical) would say it did any harm but they have a vested interest.

 

Update

The infestation has not increased and the ladybirds have started to arrive in large numbers. A lot of them are crawling around around on the ground so I have to be extremely careful where I tread when picking beans.

This influx of ladybirds has given me more food for thought. A reasonable proportion of them are Harlequins. Should I despatch them before they start attacking our home grown ones - which they are not doing at the moment - or let them continue munching blackfly?

We also have, literally, thousands of little hovering insects that look a bit like a cross between a bee and a fly (a little bit smaller than a fly) that are happily attacking the blackfly as well. No photo at the moment but any idea what they might be?