Outlook on Agriculture

As experience in the use of pesticides has been gained, new technology has been developed to ensure the safety of those involved in the handling and mixing operations, and those at risk from drifting spray droplets. This article describes recent California legislation and the equipment devised to comply with it. Factors influencing terminal velocity and settling rates of spray particles are discussed, and a comparison is made of the drift fall-out from various types of spray generators.

The post-World War II availability of aeroplanes and pilots and synthetic insecticides provided Canadian forest managers with the means of controlling devastating plague outbreaks of spruce budworm. Subsequent adoption of ULV spray rates, definition of the biologically optimum droplet size, and development of aerial spray generators such as the Micronair and Beecomist, have since given rise to an effective and environmentally acceptable forest protection practice.

The advantages of pesticide spraying at low volume and with controlled drop size and spectrum are, by now, widely accepted in principle. Rapid advances in sprayer design have overcome many of the physical and mechanical problems encountered. The UK Weed Research Organization has concentrated on evaluating the biological effects of these developments. In general, herbicide spraying by CDA has given encouraging results but many questions remain unanswered.

Post-emergence herbicide application has always presented problems of drift and insufficient selectivity. Recirculating sprayers and a variety of ‘wipe-on’ applicators have been developed more to counter such difficulties than to conserve spray material though, clearly, with the high cost of chemicals, minimal dosage is an important factor. The development of rope wick applicators to apply glyphosate has made most progress, but much remains to be learned in this new technology.

Conventional high or low volume spraying of large widely-spaced orchard trees has been shown to be grossly inefficient. Whilst little more than a third of the spray may be totally wasted, much of the remainder is deposited by wind-borne drift, very unevenly, and many leaf surfaces may receive no deposit at all. Improvements in efficiency and economy are seen in the planting of dwarf hedgerow trees and the use of shielded re-circulating controlled-droplet sprayers.

Hydraulic sprayers, which have reached a high degree of sophistication, have long been seen as inappropriate for use in many countries where crops are most at risk from pest, disease and weed competition. ULV application by spinning-disc sprayer may have overcome problems of inadequate water supply, but, for many, costs are still too high. Recent developments in electrostatic sprayers could remove this final constraint to adequate crop protection for the peasant farmer.

The advent, largely in the past two decades, of highly-active but expensive pesticides, has been accompanied by the realization that most spraying operations are inefficient, wasteful, potentially hazardous to non-target organisms, and dependent on a plentiful supply of clean water. ULV techniques, particularly those using spinning-disc sprayers, have already radically changed spray technology. Charged-particle sprayers such as the Electrodyn may completely transform it.

Tractor-drawn and self-propelled crop-spraying machinery has evolved as a result of the coming together of automotive power, mechanical engineering and the post-World War II demands of a rapidly-growing agrochemicals industry. Escalating costs of pesticides and the need for greater precision in their application have led some spraying equipment designers to turn to electronic control systems. Is this recent development justified, or is it a costly and unnecessary refinement?

The need to spray crops under less than ideal ground conditions and the trend towards very low volume applications have led to a consideration of a variety of unconventional methods of spray delivery. Balloons, kites and remote-controlled model aircraft may appear far-fetched, but should not be dismissed without proper trial. Low ground-pressure all-terrain vehicles and hovercraft appear to be the most practical alternatives to tractors or aircraft in UK agriculture.