14 June 2002

SUSTAINABLE FARMING: 7

NATURAL PEST CONTROL

All crop pests have natural enemies, in the shape of either other pests or diseases, says Dr Judith Pell of IACR-Rothamsted.

"The challenge with all natural enemies is to find a way of managing them to enhance their activity," she says. "They often come into the crop too late to help with pest control, or they may only exist in certain habitats."

Cereal crops dont have an aphid problem every year, so natural control must work, she adds. "Parasitic wasps and hoverflies are two beneficial insects which can have an effect. The key is to make better use of field margins, so they can help with aphid control."

Wild flower management is important. "Female hoverflies have to feed on pollen to produce eggs. So having wild flowers in margins increases hoverfly numbers."

Carabid beetles on the ground also have a role. "Establishing beetle banks is quick, easy and wont cost much. And the effect can be surprising."

The most common fungus that infects and kills aphids in the UK is Erynia neoaphidis, says Dr Pell.

"It only infects aphids and can eliminate populations at a local scale. The fungus produces infective spores that are highly mobile and carried between aphids by air currents or on beneficial insects."

Using field margins as reservoirs for the fungus is the focus of current research work and involves identifying suitable host plants and susceptible aphid species. Nettles look to be useful hosts.