Aphids (such as greenfly and blackfly) appear on leafy vegetables at this time of year, and they need controlling.

As the aphids congregate on the growing tips of vegetable plants, beneficial insects will start to eat them, so that the aphids will gradually disappear after a few weeks. These beneficial insects include ladybirds, green lacewings and larvae of hover flies, which all feast on the aphids.

Beneficial parasites (such as small wasps that don’t sting humans) don’t eat the aphids, they lay their eggs inside the adult aphid. The baby wasp develops inside the aphid, causing the aphid to die. The new adult wasp eventually emerges from the carcase of the aphid host,and flies off to find more aphids to use as egg nurseries, causing the next lot of aphids to die.�

If insecticides are used to kill the aphids, the chemicals will also kill the beneficial insects. To keep the good guys around, remove aphids from vegetables with sharp streams of water or a mild, soapy spray (one squirt dish soap plus 1 teaspoon vegetable oil plus 1 litre water). This will get the pests off your vegetables, but leave the good bugs around to attack the aphids.

Wash the aphids off the vegetables regularly, to give the beneficial insects time to build up and do their job.