20 February 1998

Mapping for cleavers OK if youre big

MAPPING weeds and patch spraying accordingly could save money. But with aggressive weeds like cleavers, heavy yield losses and harvesting problems could catch the unwary.

Anne Willington, who runs a GPS service from Bury St Edmunds, Suffolk, reckons fields must be intensively mapped for the system to work.

In March last year she mapped about 50ha (124 acres) on an Essex boulder clay farm. The job took an average of about 1hour for 10ha.

"Cost would be prohibitive for weed mapping alone. But if I am soil sampling at the same time, it would probably only add on another £3/ha," says Dr Willington.

She first counted cleavers numbers within a series of quadrats and used this information to visually classify populations along each tramline as high, medium or low from an ATV.

"The distribution pattern was typical. One field had virtually no cleavers, in another about half had none while the rest was heavily infested. The third field came in-between," recalls Dr Willington. "The grower is seriously considering patch treatment. That could significantly reduce his herbicide cost."

It is too early to tell whether populations will move over time. "We would need to remap weeds annually for four to five years to find out."

Derek Wade, a research consultant based at Rosemaund ADAS Research Centre, says most farmers could use a field walking service to map cleavers.

"GPS mapping may suit the big East Anglian growers but I dont think its appropriate for smaller scale growers," declares Mr Wade. "You dont really need elaborate technology, just a bit of time."

Roger Bryan, an agronomist for O N Management, an independent consultancy covering southern England, warns against easing back too much. Studies at IACR Long Ashton have shown just one cleaver in 2sq m reduces cereal yields by about 2%, he points out.

Mapping can save herbicide costs, he adds. But, headlands excepted, it is a difficult and time-consuming job. Rapid aerial infra-red imaging or similar new technology could solve the problem.

Heavy cleavers infestations are easy to identify. But lighter scatterings are less easy to spot. "If a field has a few patches with an odd one in-between, usually I would advise spraying the whole fields."

He prefers to wait until weeds present a good target and are growing well. Active growth is important with Starane (fluroxypyr) when rates can be cut with more confidence, he suggests. But he is reluctant to use less than 0.5litres/ha of Starane and 20g/ha of Eagle (amidosulfuron). Go lower, and stunted cleavers can still set seed.

A very heavy cleavers infestation may demand February or early March control. Mr Bryan prefers Eagle in cooler weather. However, speed of kill is slow. "Its not very farmer-friendly." &#42

Cleavers mapping is still at an early stage but could save growers money, predicts Anne Willington.