Aphids are soft-bodied insects that usually congregate on the growing tips of young plants. They suck the sap and excrete the excess as a sticky residue (honeydew), which falls on foliage where it can turn mouldy (sooty mould). Aphids can also carry diseases and viruses from plant to plant.

Control

Aphids can be killed by most insecticides, including the selective systemic insecticide, pirimicarb. This leaves beneficial insects such as lace-wings or ladybirds unharmed. Many organic gardeners use insecticidal soap. In the greenhouse, a predatory midge called Aphidoletes may be used. Control can also consist of encouraging beneficial insects by planting companion crops. For example:

• Poached egg plant (Limnanthes douglasii) and dwarf morning glory (Convolvulus tricolor) will attract ladybirds and hoverflies.
• Chives will repel aphids.
• Nasturtiums attract aphids. Plant them near to crops or flowers you want to protect - the aphids should attack the sacrificial nasturtiums instead.