✍ Scribed by Graham A Matthews; Neale Thomas
No coin nor oath required. For personal study only.
The present status of Integrated Crop Management requires the judicious use of pesticides to optimise yields. However, considerable concern about the possible impact of pesticides on the environment and the need to minimise the dosage applied has led to a con¯ict between the requirements for ef®cient application and avoiding spray drift. The requirement for no-spray buffer zones for certain pesticides has encouraged wide-scale adoption of coarser sprays to reduce downwind drift. However, use of larger spray droplets in coarse sprays does not always provide ef®cient delivery of a pesticide to foliage, so a higher dosage may be required to achieve effective pest management. Within treated ®elds a higher proportion of the pesticide may be lost to the soil when coarse sprays are applied, thus increasing the risk of adverse effects, such as in®ltration and potential risk to ground water within a treated ®eld.
The need, therefore, is for a method of optimising pesticide delivery whilst minimising the risk of both exo-drift downwind to neighbouring land and endo-drift losses within a treated ®eld. One approach is to optimise nozzle selection for most of the ®eld and change to a coarse spray for the downwind edge of the ®eld, while the area treated within a ®eld can be restricted to the speci®c parts infested with weeds by patch spraying. Some farmers now use air assistance to improve projection of spray droplets into a crop canopy, especially the downward-directed air curtain used in arable crops, but many food crops have a complex crop architecture which requires a more site-speci®c targeting of a pesticide if minimal dosages are to be applied.
A new nozzle concept directs a fan-shaped air jet at a shallow angle at the spray sheet emerging from a hydraulic nozzle. This affects droplet production and provides a ®ner spray entrained within the air ¯ow directed at the crop. Wind tunnel assessments with a prototype nozzle indicate less potential drift despite application of smaller droplets. The main advantage of linking the air ¯ow to individual nozzles is that they can be positioned to project spray more selectively in relation to crop architecture and pest habitat.
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