Curled leaves are generally a sign that that you have an infestation of aphids on your plants. These tiny little insects suck the sap out of the leaves, causing the leaf to distort and curl. They also secrete a sticky solution called “Honeydew” which can cause the growth of black sooty mould. If you uncurl a leaf, you can see the aphid colonies, which are often covered in sooty moulds. You may also spot white skin remains, left behind from metamorphosis.
Aphids can cause various issues, ranging from ornamental problems - leaf distortion and general unsightliness, to the spread of virus’s and weakening of plants.
Before you jump for the spray, it’s worth checking to see if you have any natural predators clearing up the aphids for you. Ladybird and lacewing larvae will polish up numerous aphids in a day, as will hoverflies, spiders and wasps. It’s worth remembering that what you use to kill the aphids will also kill their natural predators.
If you have the stomach for it, squishing the colonies with your fingers is also very effective. Disgusting though…
Ladybird and lacewing larvae - the good guys!