MAKEUSEOFMARGINSFORNATURALAPHID CONTROL
MAKEUSEOFMARGINSFORNATURALAPHID CONTROL
Wildlife-friendly farming is all the rage. So a project designed to make the most of
wildlife headlands, to better exploit natural aphid predators, could have widespread
appeal. Louise Impey reports on the novel projects current state of play
MAKING better use of field margins so they help provide effective aphid control is the objective of a major research project that was due to be profiled at Cereals 2001.
Currently under way at IACR-Rothamsted, The Game Conservancy Trust, CSL and SAC, the LINK project follows on from MAFF-funded work already done on increasing the natural control of aphids, says project leader Wilf Powell.
"Cereal crops dont have an aphid problem every year, so we know that natural control does work. But the beneficial insects are sometimes late to arrive and the aphid population is able to increase very rapidly and get away."
With his colleagues, Dr Powell is looking at ways to manipulate levels of natural enemies using field margins. Parasitic wasps and hoverflies are two of the beneficial insects under investigation.
"Parasitic wasps play a very important role in aphid control, especially at the beginning of the season. If they are present at the start, they put a brake on the aphid populations rate of growth. Then other predators, such as ladybirds and hoverflies, come in and help.
"But if the aphids arent checked in the first few weeks, they soon get out of control and the grower has little choice but to spray."
Early season synchronisation is one of the aims of the project. "In a mild winter, the parasitic wasps remain in the crop with the aphids. Then they are present when they are needed."
Cold weather and BYDV control measures disrupt that cycle. "Cold kills off the aphids that contain the overwintering parasites in the exposed crops. BYDV sprays in the autumn have the same effect. So we are trying to build up a reservoir of parasitic wasps in the field margins, concentrating on those relevant to current agri-environment schemes."
Aphid sex pheromones are being used to attract the wasps to field margins in the autumn. "These pheromones are then moved into the crop in the spring, so we get the wasps to move just as they are needed to control the first aphids."
The pheromone used is extracted from the catmint plant and incorporated into a plastic rope or strip, which releases the chemical slowly. Work being done by the Game Conservancy Trust is looking at the distribution of both aphids and predators within a field and determining how that is affected by field size, agronomic practices and margin management.
Increasing hoverfly numbers by wild flower management in field margins is a further aspect being investigated by CSL. "We know that female hoverflies have to feed on pollen to be able to develop eggs. So having wild flowers in field margins can help manipulate populations," says Dr Powell.
Discovering which flowers are best for this purpose is another aim of the work. "Hoverflies are important because they come into the crop later in the season and help keep aphid numbers in check. Carabid beetles also have a role."
Aphid alert
Project leader Wilf Powell warns that aphid problems tend to develop after a cold snap in the winter, because the natural balance has been upset. "So growers could be up against it this summer. Aphids will start flying into crops in May and June, so it will be worth monitoring populations this season."
Project partners
The LINK project – 3D Farming: Making Biodiversity Work for the Farmer – has government sponsors MAFF and SERAD. CWS Agriculture, Dow AgroSciences, HGCA, HDC, PGRO, Tesco, Game Conservancy Trust, Unilever, UAP, IACR-Rothamsted, CSL and SAC are also participating.
HOWIT ISDONE
• Use parasitic wasps and hoverflies.
• Make best use of wildlife headlands.
• Flowers boost predator numbers.
• Pheromone lures encourage to crop.