Pesticide labels for orchard spraying in the UK express dose as amounts of the product to be applied per unit ground area, regardless of tree size or branch density, and for many pesticides, regardless of crop growth stage. Before this research had started, it had long been known that this practice probably resulted in wide variation in deposits above the minimum for biological efficacy and thus was wasteful for many applications. The potential wastefulness of this practice was also recognised by various fruit growers, adopting ad hoc methods of dose adjustment to reduce pesticide usage. In a series of Chemical Regulation Directorate (CRD) sponsored research projects, undertaken collaboratively by Dr Peter Walklate (formerly Silsoe Research Institute) and Prof Jerry Cross (East Malling Research), the PACE method of dose adjustment was devised, developed, tested and transferred into practice.
PACE emerged from previous research projects PA1710 (1/1/97 – 31/12/99) and PA1721 (17/1/00 – 30/12/01). These early research projects lay the foundation for improving dose adjustment methods for commercial orchard spraying. For example, specialised spray tracer methods were developed to enable the measurement of deposit distribution on a wide range of commercial orchard structures and a tractor mounted scanning LIDAR system was developed to make rapid non-invasive recordings of orchard structure. New data analysis methods were subsequently developed to take advantage of the probabalistic description of orchard structure based on LiDAR measurements. From the synthesis of results obtained with these methods, dose adjustment was identified as the most effective basis for: improving the efficiency of pesticide use and mitigation of off-target drift contamination from commercial orchard spraying in the UK.
Research projects PA1732 (1/11/01 – 31/1/04) and PS2002 (1/8/04 – 31/7/07) were aimed at supporting the practical development of the UK PACE scheme for dose adjustment including: efficacy testing, farm-scale integration with different planting systems and different types of tree fruit. The first PACE scheme for apples was presented to UK growers at four special workshops held within the main areas of pome fruit production in the UK during February and March 2006 together with publication of an attendant HDC Factsheet. This scheme combined advice on sprayer calibration with structured assessment of the need to adjust the sprayer output based on knowledge of the pesticide type and grower assessments of: canopy density, height and row spacing. A pictographic key was constructed from LIDAR images of selected canopies to show the relative density of different apple orchards at the pre-blossom and full-leaf growth stages. This key was also made available on the CRD website to identify the scope of the scheme for UK pesticide registration. The Crop Adjustment Factors was devised to represent the dose adjustment for canopy density according to the fraction of the max label dose and these were published in the Efficacy Guideline 403, (Defra 2006). The scheme also introduced the concept of a standard orchard to help growers establish a reference structure for the purpose of sprayer calibration at full label dose rate.
Research project PS 2018 (1/6/08 – 31/5/11) was aimed at simplifying the original PACE scheme for the grower by reconstructing it as a webpage linked system to improve the flow of information and the quality control of input and output. This system used a generalised dosage model for efficient product use. Also, new crop structure standards were created to demonstrate a practical method for supporting any of the popular methods of label dose rate expression.
The information that has been accumulated through the, now standard, use of scanning LIDAR recordings of orchards has been a useful resource throughout the last decade for analysing key regulatory problems, including: European harmonisation of dose expression for pesticide registration and new European aspirations for efficient dosage of orchard spraying products. Other results from this body of research are being used to establish a better understanding of bystander drift contamination from commercial orchard spraying.