Orchard spray application in Europe – state of the art and research challenges

Axial fan airblast sprayers are still the most commonly used for orchard spray applications in Europe because they are of comparatively low cost, robust, durable and flexible for use in a wide range of orchard types though they are gradually being replaced by more efficient and better targeted designs. Axial fan sprayers normally produce a large radial spray plume that is poorly targeted and which results in high spray losses to the ground and as spray drift, and growers rarely make adequate adjustments to optimise sprayer performance in particular orchards.
A wide range of other machine types are also in use including cross-flow designs and those with ducting which aim to better target the spray plume to the tree, with varying degrees of success. Several designs of tunnel sprayer to reduce spray losses are available but tunnel sprayers are only used by a few growers because of their high cost and practical difficulties of use. Multi-row sprayers are being increasingly adopted to increase work rates. Sprayers with canopy sensors that adjust sprayer output (spray liquid and/or air flow rate) in real time in response to the physical characteristics of the target and/or environmental conditions are currently at the cutting edge of spray machinery development. There has been a gradual evolution from simple machines where nozzles are switched off in response to gaps in the canopy to those that make adjustments in real time in response to target canopy size and density. Such sprayers have been shown to be considerably more efficient and there is a key need to foster adoption into practice.
Spray drift and environmental contamination rates from orchard spraying are high compared with arable crop spraying and a range of methods of drift mitigation of varying degrees of effectiveness and practicality have been developed, some of which are now legally required, notably mandatory buffer zones on pesticide labels and the use of low drift air induction nozzles which produce very coarse spray qualities. There is considerable variation in mandatory schemes in different EU countries, which need to be harmonised. There are important changes in the way dose rates are being expressed on pesticide labels and efforts are underway to develop methods of adjusting dose rates to suit the very wide range of orchard canopies to achieve deposits that are more uniform between different canopy sizes at different growth stages. Regular sprayer testing is now mandatory in many countries, to ensure that sprayers are adequately maintained and calibrated.
There is extensive scope to improve many aspects of orchard spray application by research. The three most important key challenges are 1) Improving machine design and crop adaptation to improve deposition/reduce losses including in real time 2) Understanding spray deposits/quality/cover and their effects on efficacy 3) Dose adjustment.
In this paper, the state of the art of orchard spraying practice in Europe including machinery, air adjustment, atomisation/nozzles, canopy sensing, drift mitigation, dose expression and adjustment and sprayer testing are broadly overviewed and the main technical and research challenges presented.