How spray drift can be cut with higher barriers

20 March 1998




How spray drift can be cut with higher barriers

SPRAY buffer zones to protect watercourses could be narrower in future if more attention is given to the type of intervening field margin.

That is the thinking behind new Willmot Pertwee trials at Radcot Bridge Farm, Faringdon, Oxon, where the farming and conservation benefits of sown margins have been investigated for a decade.

"Nobody has given due consideration to the height of margins or their composition," claims Marek Nowakowski, the firms conservation specialist.

Application banned

Currently many pesticides may not be applied closer to watercourses than 6m (20ft). The LERAP approach (Arable Feb 27) would allow that figure to be reduced under certain circumstances, for example where windbreaks are in place.

But in its latest proposals the Advisory Committee on Pesticides says it needs evidence of their effectiveness before building them into any system.

The new field trials follow tests by Zeneca at Jealotts Hill last harvest where spraying was done beside strips of wheat of three heights – an uncut stand, the crop with just the ears removed and a stubble, explains Mr Nowakowski.

"The data shows there are massive differences in drift catching capability. A strip 1m wide by 1m high stops more drift than a 6m strip 50cm high. So width is only one component. It is not the beginning and the end."

Weeds stopped

Structured and managed properly, sown margins stop weeds invading fields from the edges and offer an opportunity to extend and diversify countryside habitats, he adds.

"Yield mapping shows the edges of fields can often lose growers money. So why farm them?"

Willmot Pertwee offers a range of practical options to suit individual requirements. "The key is deciding what the farmer wants," he stresses.

Where water protection is a priority it should be possible to determine the best anti-drift structure. Grants from the Countryside Stewardship Scheme could help offset the cost, provided the margins is acceptable.

The latest experiment, beside a brook for reality, is comparing 20m x 6m (66ft x 20ft) plots naturally regenerated against several different sowings, each established with and without herbicide. These include a perennial grass mix both with and without extra herbs, and a tall grasses and flower mix. "We have also got some plots with deep-rooted species to see whether we can soak up nutrients from the sub-surface."

Planting trees or hedges as watercourse spray barriers may be a bad move because of the risk of their roots blocking land drains, he notes.

"We are managing the plots long term and studying the drift by putting water-sensitive paper in transects across the margins on spraying days. We are also spraying water on windy days and measuring where the drift is caught."

Narrower barriers

Once proven, narrower barriers could be built into the LERAP scheme through a system of certification, suggests Mr Nowakowski. "As with set-aside the farmer would submit the various claims and proposals of what he had done." These in turn could be checked by visiting agronomists trained to verify that the barrier/buffer fell into a particular category.

BUFFER STRIPS

&#8226 Height and composition ignored.

&#8226 Windbreak effect acknowledged.

&#8226 Trials evidence lacking.

&#8226 Dramatic height effect in test.

&#8226 LERAP certification scheme?

Higher margin vegetation could protect this stream from spray drift, according to Marek Nowakowski. Trials are under way to find the most effective seed mixtures to provide such a buffering effect.

BUFFER STRIPS

&#8226 Height and composition ignored.

&#8226 Windbreak effect acknowledged.

&#8226 Trials evidence lacking.

&#8226 Dramatic height effect in test.

&#8226 LERAP certification scheme?


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