Patch spraying: future role of electronics in limiting pesticide use

Developments relating to the control of application equipment can deliver improvements in pesticide use by better matching applications to target requirements. This may have components relating to the spatial distribution of a weed, pest or disease or methods by which the target, particularly a crop canopy, can be described with respect to a given application. Changes in application can relate to the dose and/or volume applied, but may also concern the way in which a treatment is delivered in terms of parameters such as spray trajectory angle and droplet size distribution. For many weed species there is evidence of patchy distributions in field situations. Studies have shown that savings of typically up to 40% in herbicide use can be achieved by adopting patch spraying approaches in such situations. Weed patch detection is key to the performance of such patch spraying systems. In widely spaced rowcrops such as vegetables, there is considerable scope for developing fully automated detection systems based on image analysis, and for the development of accurate guidance systems that apply pesticides only to the crop row. In crops with a relatively high plant density, weed detection in the medium/short term is likely to be based on manual discrimination. The costs of labour for manual weed patch mapping have been estimated at less than 1.50 ha(-1) pounds sterling. Potential savings in pesticide use can also be made if applications are matched to crop canopy structure. This is most important in bush and tree crops where savings of up to 75% in pesticide use could be achieved. In crops such as cereals, studies have shown that savings in fungicide use may be possible, particularly at earlier stages of growth by adjusting spray delivery to measured canopy characteristics. Key components of the performance of application systems concern the ability to deliver over a dose rate range of more than 3:1 while maintaining control of variables such as delivery trajectory angle and spray quality. Traceability and the effective monitoring of applications is likely to be a major driver influencing the uptake of more sophisticated control systems. Methods of labelling pesticides with systems that can be read by the application unit will be an important step in the development of recording and data handling systems that will operate safely with the minimum of operator input and enable the environmental advantages of targeted pesticide application to be monitored.