You can use Rhubarb or elder leaves as a herbal pesticide because of their high acid content – and they are also usually available in large quantities and not wanted for other uses. There are also a number of other herbs you can use if you haven’t got any Rhubarb.

To make a Herbal Pesticide:  I simmer about 1lb of Rhubarb leaves in about 3 pints of water in an old pan with a lid on I save for such uses (though don’t use aluminium pans.)  Simmer for about half an hour and then store in a cool place, dilute with another 3 pints of water and use within week or so. If you’ve only got a small garden then cut the recipe by a third to make 2 pints of pesticide when diluted.

Another recipe: Also useful for rot or disease -  make an infusion of chives or garlic cloves (4 cloves to 2 pints)  dilute and use straight away when cool.