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A review of methods of reducing drift without compromising product efficacy - PS2010

Many developments associated with boom sprayer and agricultural nozzle technologies over the past decade and longer have aimed at delivering drift control. Such developments have been recognised in schemes such as the Local Environmental Risk Assessment for Pesticides (LERAP) scheme where the width of a buffer zone used to protect surface water from contamination by drift can be reduced if drift reducing technologies are used. It is also important that such drift reducing methods maintain product efficacy so that the dose of pesticide required to give a defined level of response does not need to be increased.

Timeliness is a major factor influencing the performance of agricultural pesticides an is improved by systems taht are able to operate in a wide range of conditions and achieve high work rates. For boom sprayers, work rates are increased by increasing the forward speed while spraying (e.g. from 8.0 to 12.0 km/h), increasing boom widths (e.g. from 12 to 24 m) and by using lower volume rates (e.g. 100 rather than 200 L/ha). However, all these changes tend to increase the risk of drift when using conventional systems.

Initial methods of deliverying drift control did so by using nozzles such as the pre-orifice design that increased droplet size. Although droplet bounce from leaf targets was reduced by the lower droplet velocities from such nozzles compared with conventional designs producing the same droplet sizes, there was still some evidence from field trials that the use of such nozzles compromised product efficacy particularly when treating small targets.
The development of nozzle systems generating spray droplets with air inclusions (twin-fluid and air induction nozzles) gave sprays with large droplet sizes that were likely to give good drift reductions and high levels of retention on leaf surfaces because the presence of air in the droplet gave a mechanism for energy absorption on impact and hence less chance of bounce. However, such systems gave relativlely low numbers of spray droplets when compared with conventional nozzles particularly when operating at low volumes. There was therefore an increased risk that small targets would receive an inadequate dose for good control and/or larger target surfaces would have variable deposits such that efficacy would be reduced.

Results from field trials conducted in a number of countries with drift reducing nozzles systems suggest that there are circumstances when such systems can deliver high levels of drift control without posing a substantial risk to product efficacy. In other circumstances product efficacy is influenced and control levels reduced. This work aims to review the data that is now available and make recommendations relating to the use of such systems that will enable higher levels of drift reductions to be achieved in routine field applications.

The use of air assistance (a concurrent air stream ducted with the spray) is also a technology that enables drift to be reduced with little or no implications for product efficacy in many circumstances. These systems will also be included in the review.

Data relating to the drift risk from different nozzles can come from field or standardised wind tunnel tests. Published work has shown that nozzles with similar outline specifications in terms of spray angle and flow rate can give very different droplet size distributions with implications for both drift control and product efficacy. It will therefore be important in the review to identify the physical charateristics of sprays associated with defined levels of drift control and product efficacy.

The report of the work will provide a basis for The Pesticides Safety Directorate to review the approach taken to the use of drift reducing application systems.
To review the available information that can link the ability of nozzle designs such as the air induction system to control drift with the minimum risk to product efficacy and to make recommendations relating to:

(1) how applications in sensitive areas could be made to use the available spraying windows most effectively while reducing the overall drift risk; and

(2) the generic advice that may be appropriate regarding the use of different nozzle designs and droplet size spectra in different pesticide applications (e.g. advice on product labels or via leaflets detailing appropriate nozzle selection options/application strategies when applying different types of plant protection products (PPP’s) or relating to the use of different products against specific targets).

Specific objectives relate to:

1. Collecting data relating to drift reduction and efficacy of application systems based on the boom sprayer and designed to reduce the risk of drift by searching the existing literature.
2. Collecting data relating to drift reduction and efficacy of application systems based on the boom sprayer and designed to reduce the risk of drift by discussions with European Centres involved in the collection of such information.
3. Collating the data obtained particularly linking drift control and efficacy: nozzle systems to be defined in relation to the physical characteristics of the sprays produced (droplet size and velocity distributions together with the spray volume distribution pattern) with additional measurements made if required.
4. Analysing and interpreting the data and results obtained;
5. Reporting the findings to Defra and The Pesticides Safety Directorate.

Project Documents
• Final Report : A review of methods of reducing drift without compromising product efficacy   (503k)
Time-Scale and Cost
From: 2006

To: 2006

Cost: £25,888
Contractor / Funded Organisations
Silsoe Spray Application Unit
Crop Improvement              
Environmental Effects              
Pest and Weed Control              
Pesticide use              
Plants and Animals              
Fields of Study
Pesticide Safety