Only this morning I was talking to a fellow allotment holder about black fly.
He maintains that Rhubarb Juice is what he has always used, and it works for him. Never having heard of it I got home and googled it. It's free and is a lot cheaper than Provado .. I paid £10 for a bottle last week end.
He says he just tears the leaves up and puts them in a bucket covered in water for a few days. Pours it through a sieve and then sprays it on everything.
When I Googled it I found the method shown below ..
Spray rhubarb spray
- the oxalic acid in rhubarb leaves can help to control aphids, particularly on roses.
Cut 450g (1lb) rhubarb leaves, place in an old saucepan (the oxalic acid may damage one that you still use) with 1.1 litres (2pt) water and boil for half an hour, topping up as necessary. When cool, add 1 dessertspoon of soap flakes dissolved in 275ml (1/2pt) warm water. This acts as the wetting agent when added to the strained rhubarb liquid. Stir the mixture thoroughly and use undiluted as a spray. Rhubarb leaves are quite toxic so be careful to keep this away from children and pets.