Today 
Sap-sucking aphids excrete honeydew, sometimes seen as a string or web of stickiness. This can drip down on to lower leaves and on to other plants. A dark or grey-green mould then spreads across the honeydew. It's unsightly and prevents light and air from reaching the leaves.
Solution
Organic
There's no control for sooty mould, but you can control the aphids. Outside, natural predators such as birds and ladybirds are your best allies. Ladybirds can be bought as a biological control, and you can also buy ladybird houses to encourage these helpful creatures to take up residence in your garden. They need time to tackle the problem, so don't expect them to hoover up the aphids overnight. Small clusters of aphids can be squished with your fingers or washed off with a strong jet of water.
Chemical
Bifenthrin, imidacloprid and thiacloprid will deal with aphids, but check the label carefully if you're using them on edible crops.
