"The geometric structure of trees can vary enormously even on the same farm, so you cannot spray them all in the same way," said Cross. "But the label gives the same dose per hectare for all orchards."
Under a Defra-funded project, Cross and colleague Peter Walklate developed a way of using a LiDAR (light detection and range) device and accompanying software to measure and record trees' canopy height, width and, most crucially, density.
The two research partners then created an algorithm designed to transpose this data into a factor for tailoring the dosage rate, and a tool for this, PACE (Pesticide Adjustment to the Crop Environment), has now been made available free online at www.pjwrc.co.uk.
"It is quite complicated, but you do not need to know (how the algorithm works) in order to use it," Cross explained.
"We have trialled PACE over the last two seasons on seven farms, including some of the largest growers in the country, yielding some substantial savings."
Already product labels are including advice to apply "an appropriate dose adjustment scheme" such as PACE before spraying, he noted, adding that other EU member states have developed their own such schemes and that efforts to harmonise this work "have got stuck".