28 November 1997

Nozzle drift index will help get spraying right

A SCHEME which could help spray operators cope better with buffer zone restrictions is just around the corner.

The new scheme builds on the current BCPC Spray Quality classification by introducing the idea of a drift index for nozzles. This should help users choose the most appropriate ones for particular circumstances, explains Ted Southcombe, AgrEvos head of applications.

Developed by a group of international specialists, the system has been delayed by difficulties categorising the drift potential of nozzles which produce droplets containing air (such as the Airtec).

The scheme is based on results from field and wind tunnel research. "We see it as a big step forward," says Tom Robinson, sprayer specialist with Novartis. "At the moment 6m buffer zones are based on worst case scenarios."

Combined with sensible adjustments of forward speed, the new classification is expected to make it easier for growers to achieve a proper balance between spray performance and environmental protection, he explains.

The idea has been put to the regulatory authorities for discussion in the context of LERAP – Local Environmental Risk Assessment of Pesticides (see Arable Aug 1). It might permit conditional use of certain products closer to water courses and other environmentally sensitive areas.

Eventually product labels could refer to both the spray quality required and the acceptable drift potential. Products posing no real threat to uncropped areas might be labelled Apply as a "MEDIUM" spray with "NORMAL" drift potential. Those which should not find their way into such areas could be tagged Apply as a "MEDIUM" spray with "LOW" drift potential.

However the terms for defining drift ratings are still being worked on. Manufacturers clearly prefer not to have their products branded high drift potential, says Mr Southcombe.

Once all aspects are agreed the aim is to issue technical notes to guide operators.

Water boards in the Netherlands are taking a growing interest in which nozzles growers use, according to researcher Jan Van de Zande. "We are expecting something next January within the Water Authority regulations."

Drift reduction trials have yielded useful information on nozzle performance, say Paul Miller (left) and Ted Southcombe.

SPRAY SCHEME

&#8226 BCPC guidelines.

&#8226 Based on field and lab work.

&#8226 New drift potential index.

&#8226 Could aid LERAP decisions.