New developments in pesticide-application technology

CROP PROTECTION (1982) 1 (2), 131-145 © 1982 Butterworths

New developments in pesticide-application -technology G. A. MATTHEWS

Overseas Spraying Machinery Centre, Imperial College at Silwood Park, Ascot, Berkshire SL5 7P Y, England ABSTRACT. Greater awareness of the inefficiency of pesticide application, water-supply problems, the need for more rapid and timely treatment, and the increased cost of pesticides, have stimulated development of new application techniques. Changes in nozzle design can produce sprays with a narrower droplet spectrum; the introduction of electrostatically charged sprays provides greater control of droplet trajectories to increase deposition and reduce downwind drift. Improvements in hand-carried, vehicular and aerial spraying are briefly reviewed, together with granule application and seed treatment. Introduction of closed systems to transfer pesticides from containers to the spraying equipment is expected to reduce operator contamination; this will be combined with a trend towards spray equipment with microprocessor controls, and further development of pesticide formulations.

Introduction Development and marketing of a new pesticide is now extremely expensive because of the increased costs of safety evaluation, which is necessary to meet national and international registration requirements. Only a small fraction of the development costs are devoted to consideration of how the product will be applied, because the majority of pesticides are formulated for dilution in water and are applied through hydraulic sprayers, despite the widely accepted view that most sprays are very inefficient. According to Graham-Bryce (1977), rather less than 1°/o of an insecticide normally reaches insect pests within foliage. Even when foliage itself is the target, up to 70~o of a spray may be lost at the time of application. Other losses are caused by incorrect timing of application, which can be exacerbated by a lack of adequate equipment. Several factors have now stimulated greater consideration of application techniques. In the tropics, ultra-low-volume (ULV) spraying has been necessary in areas where water is difficult to collect from seasonal streams or bore holes and transport is by headloads to fields, often over considerable distances. In temperate regions, prolonged wet periods or strong winds have limited the time available for spray applications; farmers have therefore needed quicker methods to treat large areas when weather conditions are favourable. Both these trends have been reinforced by the increased costs of petroleum-based products such as pesticides,

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and the increased frequency of spraying associated with more intensive crop production. This paper examines the new developments which have occurred during the last decade and attempts to forecast the future development of application systems. Nozzle

design

Hydraulic nozzles remain the most widely used method of producing a spray, as the nozzle tip is relatively cheap and easy to fit. The main trend has been away from brass or steel components to various types of plastic, including polypropylene and types of nylon, sometimes reinforced with other materials. The quality of plastic tips has improved: some have good resistance to erosion and, because they are relatively inexpensive, can be replaced frequently to maintain the correct output of a machine. Plastics have been used to mould the nozzle body, with a bayonet-type cap,

FIGURE 1. Bayonet-type quick-fit nozzle assembly (Lurmark Ltd). sometimes colour-coded, for rapid fitting of the tip (Figure 1). A diaphragm relief valve as an integral part of the nozzle body is now more widely used on tractor spray booms as well as on aircraft. Changes in tip design have aimed to produce larger droplets, less prone to drift. Low-pressure fan nozzles have been used at 1 bar (100 kPa) to apply herbicides at 70-100~/ha, with a smaller proportion of the spray comprising droplets less than 100/tm in diameter (Bals, 1978). However, application of reduced volumes with small-orifice tips requires more careful filtration to avoid nozzle blockages. An alternative approach with cone nozzles has been to add an extra swirl chamber and

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outer orifice (Brandenburg, 1974) to produce very large droplets, but coverage is poor unless larger volumes are applied. Dombrowski (1975) has suggested that heat might be used to produce a narrower spectrum of droplets from a fan or cone nozzle, presumably because the sheet of liquid breaks up closer to the nozzle tip when warm. This requires an increased energy input and the nozzle has not yet been used commercially. A very narrow spectrum can be achieved by using a piezoelectric transducer to pulse liquid through an orifice (Yates and Akesson, 1978; Yates, Akesson and Brazzelton, 1981). If the droplets are electrostatically charged, they remain separate

FIGURE 2. Droplets and ligaments formed by a pulsed microjet. Electrostatically charged droplets (diameter 260 #m) remain separate. Photograph supplied by W. Taylor, Weed Research Organization, Yarnton, Bristol. (Figure 2) (Stent, Taylor and Shaw, 1981). Large droplets can be produced but only well-filtered solutions can be applied with these nozzles, as the orifice diameter must be approximately half the droplet diameter. Using an orifice size of 127 ~m, a pulse frequency of 12 000 Hz and a pressure of 41 kPa, Yates et al. (1981) obtained nearly uniform droplets of 246/~m. Spinning discs are more widely used to provide greater control of droplet size, by changing the rotational spe~d while adjusting flow rate (Matthews, 1979). On small hand-carried battery-operated spinning-disc sprayers, the trend has been towards a single small-diameter disc to reduce power requirements and to extend battery life (Figure 3). Some units have an adjustable holder to allow the number of batteries to be changed and, consequently, the voltage to be selected for different disc speeds. Other units have constant-speed motors, irrespective of voltage.

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FIGURE3. 'MicroULVA' spinning-disc sprayer. Photograph by R. Hamer, Micron Sprayers Ltd. Initial development of units on tractor sprayers involved mounting multiple discs on a common shaft (Taylor, Merritt and Drinkwater, 1976). Several discs were used simultaneously to accommodate the higher flow rates needed with faster forward speeds, without overloading the nozzle. The discs were partly shrouded to give a spray pattern equivalent to that of a fan nozzle, for herbicide application. A single cup-shaped disc (Figure 4) has now been designed to avoid the use of multiple discs and to apply up to a litre per minute, but when rotated at speeds greater than 2000 rev/min, a narrow droplet spectrum can be achieved only at low flow rates (100 ml/min), because air displacement interferes with ligament formation (Heijne, 1978). On one sprayer, partly shrouded spinning discs have been mounted vertically so that spray is directed down into the crop. Arnold and Pye (1980) have modified the disc design to enable liquid spread over the disc surface to be charged electrostatically before droplet formation. Increased deposition, particularly on underleaf surfaces, is achieved with charged sprays and biological assessment of the sprays charged with this equipment is now in progress (Griffiths, Arnold, Cayley, Etheridge, Phillips, Pye and Scott, 1981). Carleton and Bouse (1980) have developed an induction charging system on a spinning-disc nozzle for use on aircraft. Von Ganzelmeier and Moser (1980) and Law (1980) have also investigated the use of electrostatics, and a novel approach to nozzle design using only electrical forces to form ligaments has been described by Coffee (1979, 1980, 1981). In these electrodynamic nozzles, liquid is fed by gravity or a small low-pressure pump to a narrow gap at a high potential ( > 15 kV). The charged liquid develops a series of waves, from the crest of which one ligament is formed. The number of ligaments increases with increased voltage, and the thickness of each ligament depends on flow rate: droplet size can therefore be adjusted from 20 to

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FIGURE 4. 'Micromax' large spinning cup. Photograph by R. Hamer, Micron Sprayers Ltd.

200 ~m by controlling voltage and flow rate. The uniformity of the ligaments results in a very narrow range of droplet diameters for each setting. A field-adjusting electrode or counter electrode connected to earth by a trailing wire, surrounds the nozzle which, in the models being used at present, has an annular gap, although linear versions of the nozzle are possible. Correct formulation of pesticides for application with this nozzle is very important, as the resistivity must be within the appropriate range. Partial discharge of a spray is possible by adding a sharp point to the counter electrode: this allows the spray to move downwind in a similar manner to that from spinning-disc sprayers. Manually operated sprayers Lever-operated knapsack and compression sprayers remain, in principle, very similar to those designed over 100 years,ago, except that most components are now manufactured in polypropylene containing a UV-light inhibitor. Designs with large-capacity pumps to reduce the effort of pumping, a large recessed opening with a strainer for quick filling and a pressure regulator, are much easier to operate than the old models. The majority of sprayers are still fitted with a simple hand lance and single nozzle, although specialized booms have been designed to improve spray coverage (Tunstall, Matthews and Rhodes, 1961) or the speed of application (Cadou, 1959, Johnstone, Huntington and King, 1975) and to reduce operator contamination. In many areas, the 'recommended' spray volume has been up to 1000~/ha, but the sheer effort of pumping such a large volume of water, even if available, discourages farmers from applying the correct amount of pesticide. When farmers apply only a

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small proportion of the recommended dosage and achieve poor distribution of the chemical, inadequate control of pests is often followed very rapidly by pest resurgences in the absence of natural enemies. Recently, more consideration has been given to the selection of nozzle tips to reduce the volume of spray as far as is practically possible, recognizing that water supplies in many parts of the world contain particles which are liable to block nozzle orifices. The use of appropriate nozzle tips and careful filtration should ensure that spray volumes do not exceed 50-200d/ha, the actual volume being related to the area of foliage needing treatment. Herbicide application with low-volume impact nozzles is being investigated in Sri Lanka at present (R. Wijewardene, personal communication). Hand-carried sprayers Small-scale farmers in the tropics have used hand-carried battery-operated spinning-disc sprayers to treat a number of crops, including groundnuts (Mercer, 1976), tomatoes (Quinn, Johnstone and Huntington, 1975), cowpeas (Raheja, 1976) and rice (Pickin, Heinrichs and Matthews, 1981) but the principal use has been to treat cotton with insecticides (Matthews, 1981b). Spray droplets thrown from the disc are distributed in the crop canopy by gravity and air movement, so that sedimentation is on upper leaf surfaces and impaction on windward surfaces. Underleaf coverage is poor unless there is sufficient turbulence to move the leaves. Special formulations of low volatility are preferred when droplets are smaller than 100 #m in diameter, but the greater cost of these formulations has resulted in the adoption of a water-ultra-low volume (WULV) technique in some areas, principally in Malawi (Mowlam, Nyirenda and Tunstall, 1975) and the Gambia (King, 1976), in which wettable powder formulations are applied to a single-row swath in 15 litres of water per hectare. Normally, wider swaths are used, especially on small cotton, but better coverage is generally obtained with narrower swaths to even out the effects of variations in wind speed and strength, and this is reflected in heavier yields. Hand-held spinning-disc sprayers powered by an AC mains supply or a DC electric motor (powered by a rechargeable battery) or two-stroke engine to drive the disc and a fan to propel spray into crop canopies, have been used in glasshouses (Fuller Lewis and Sylvester, 1980; Lindquist and Powell, 1980). Like insecticides, herbicides have been applied with spinning-disc sprayers, but for this type of product, the disc speeds are generally governed at 2000 rpm to apply droplets of 250 #m volume median diameter, which sediment rapidly and reduce the risk of drift. Utulu and Akobundu (1978) reported good results in trials with paraquat and glyphosate in volumes of 20 and 401/ha compared with 350E/ha. When glyphosate was applied at 1.2 kg/ha with a spinning disc, results were similar to those with double the rate in the high-volume treatment. Wijewardene (1978) has used these sprayers for minimum-tillage systems in the tropics, and other recommendations include application of atrazine on maize (see,for example, Hernandez, 1978; Merlier and Dear, 1978). More wide-scale use of this technique awaits the results of further trials to establish appropriate dosage and volume rates for various herbicides and crops. The provision of suitably packaged products and of clear instructions is also necessary, to reduce the risk of overdosing, or use of an inappropriate chemical, which might damage sensitive crops. Garnett (1980) has developed a wheelbarrow sprayer, with pump and spinning

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cup driven by the ground wheel, to give a constant spray volume and droplet size irrespective of the operator's walking speed. The disc is shrouded to control swath width and facilitate interrow applications of herbicide. A new method Of packaging, with the nozzle incorporated in the bottle to form a 'bozzle' container holding the right amount of chemical for a prescribed area (Coffee, 1981, Matthews, 1981 a), as an integral part of the electrodynamic system of spraying, is one new approach to the marketing of pesticides in quantities suitable for the small-scale farmer (Figure 5). Only insecticides, including the synthetic

FIGURE5. The 'Bozzle' container, showing charged spray. Photograph by courtesy of ICI.

pyrethroid cypermethrin, have been formulated so far for application with 'bozzles' and electrodynamic sprayers, but further development should extend the range of products available. The high-voltage generator system used in electrodynamic spraying requires much less power than small electric motors: battery life is therefore considerably extended and, in the absence of any moving parts, sprayer maintenance is expected to be minimal. The handle of the electrodynamic sprayer is deliberately long so that the nozzle is nearer to the crop than to the operator and, as an additional precaution to reduce operator contamination, the 'bozzle' is held downwind in a similar way to the spinning-disc sprayers. When cypermethrin has been applied in a volume of

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0"5 E/ha, heavier yields of cotton have been obtained than when knapsack sprays have been used (Morton, 1981). The main advantage of electrostatic systems is improved coverage of undersurfaces of leaves, and ability to apply smaller droplets, with greater control of their trajectory into crop canopies and greatly reduced drift. For some crop/pest situations, electrodynamic nozzles may be positioned between rows to give better coverage of the lower part of crop canopies. Fogging a n d aerosols Thermal fogging is still widely used to treat glasshouse crops, although pesticides are seldom distributed very evenly by this method, and predominantly cover the upper leaf surfaces (Burges and Jarrett, 1979); however, fumigant effects can be exploited with some pesticides, provided that the fog is not dispersed too rapidly. One drawback, noted by Robinson and Wilson (1979), is that a high wind can suck fog from a poorly sealed house in 10 minutes. Thermal fogs have also proved to be useful in applying fungicides in rubber plantations, where upward convection provides coverage of tall trees. In most situations, thermal fogs are being replaced by ultra-low-volume aerosols generated by vortical nozzles to produce droplets with a VMD less than 20/~m (Mboob, 1975; Lindquist and Powell, 1980). Vortical nozzles have been used to apply microbial insecticides (Sorensen and Falcon, 1980). Vehicular s p r a y e r A wide range of tractor-mounted or self-propelled spray equipment is now available,

with the larger equipment fitted with hydraulically operated booms. Wide variations in spray deposit are caused by vertical and horizontal errant movement of the booms (Nation, 1980): the objective of research therefore has been to design suspension systems which isolate rolling and yawing motions of the sprayer from the boom. A gimbal-type mounting, with horizontal and vertical pivots through the centre of gravity of the boom (Nation and Holden, 1975), has not been widely accepted by manufacturers, who have generally preferred a pendulum suspension. Specialized booms with wheel supports are also being reconsidered. Boom stability will become increasingly important with reduced volumes of spray and faster speeds, and so will more accurate controls. Allan (1980) has discussed the various factors which need to be monitored and controlled during spray application. Forward speed and flow of spray to the nozzles can now be monitored by a number of electronic devices (Givelet, 1981) to enable the operator to regulate the equipment and maintain a selected volume per hectare. More sophisticated systems have been developed so that the monitoring system directly regulates delivery of liquid to the nozzles, but this is satisfactory in most cases within narrow limits only, otherwise the angle and droplet size of the spray is affected. Hand-held electronic metering units can now be used to measure the output of individual nozzles across a boom and facilitate calibration of sprayers. In some crop systems, notably winter-sown cereals, greater use of herbicides during the European winter has created a demand for high-speed vehicles with low-pressure tyres (Elliott, 1980; Rutherford, 1980). A number of all-terrain vehicles have been considered, including hovercraft (Johnstone, 1981), but a lightweight high-clearance self-propelled vehicle specially designed for spraying is

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needed to cope with the wide range of chemicals, including plant-growth regulators, which have to be applied at all stages of growth. Controlled droplet application (CDA) using tractor-mounted equipment has increased principally in the USA, but few reports on results achieved with the system have been published. Reviewing CDA studies in the U K , Taylor (1981) indicated that adequate weed control can be obtained with soil-applied herbicides and also foliar sprays of systemic compounds, alone or in mixtures. Contact herbicides such as ioxynil have been less effective with 250 pm droplets in 20f/ha, suggesting that higher volume rates with large droplets are needed to achieve adequate coverage. To maintain the same amount of active ingredient with reduced volumes necessitates an increase in concentration of active ingredient, but this can affect uptake and redistribution of a pesticide; further studies of a wider range of droplet sizes and volume rates are needed. Herbicide (glyphosate) activity was greater at the low volumes involved in CDA (Turner and Loader, 1978): the scope for reduced dosages will be even greater with insecticides and fungicides. A series of spinning discs mounted on a mast (Lake, Frost and Lockwood, 1978) have been used to treat a series of swaths with fungicides, plant growth regulators such as chlormequat, and certain insecticides, in a similar manner to the hand-held equipment; boom sprayers with high-speed discs are now available. Spinning discs have been mounted in the air-stream of orchard sprayers (Morgan, 1981); there has also been considerable interest in using aerial Micronair units mounted on a vehicle, particularly for fungicidal vine-spraying in Australia. The units are driven hydraulically, with the air-stream provided by the fan directing the spray into the crop. Small hedgerow fruit trees have also been sprayed by nozzles mounted in a tunnel shield to protect the spray from the wind during application and to recirculate spray deposited on the shield (Cooke, Herrington, Jones and Morgan, 1977). Specialized post-emergence herbicide applicators have been designed to utilize the height differences between crops and weeds in order to apply broad-spectrum chemicals selectively (Lutman, 1980; Wills and McWhorter, 1981). Recirculating sprayers have solid-stream nozzles directed at a large spray trap which collects 70-90% of the spray not intercepted by tall weeds. Care must be taken to avoid herbicide splashing on the crop. An alternative is the rope wick applicator (Dale, 1978; 1979) in which herbicide is supplied from a reservoir (usually a horizontal hollow boom or plastic pipe capped at both ends), by capillary movement down overlapping sections of braided nylon rope. Hand-held wiping devices are also available (Cooper, Fraser, Burrill and Deutsch, 1981). Law (1980) has developed an electrostatic spray system on a tractor-mounted sprayer using twin-fluid nozzles: studies by Arnold and Pye (1980) also have been principally concerned with tractor-mounted spray equipment. Field evaluation of a vehicle-mounted electrodynamic sprayer is now in progress (Coffee, 1981). Aerial s p r a y i n g Improved systems of swath matching using inertial guidance systems have been used in large aircraft spraying vast forests in Canada (Armstrong, 1981). Microwave systems with a 'Master' unit in the aircraft and two remote reference stations have been used successfully where aircraft are operational for prolonged periods in the area (Horner, 1980), but the high cost has so far prevented greater use. Most aircraft are still fitted with large numbers of hydraulic nozzles, despite the

140 New pesticide-application technology wide droplet spectrum achieved. Rotary cage nozzles (notably the Micronair AU3000 unit, which has a cylindrical wire gauge unit rotated by blades which can be adjusted to give a particular rotational speed) have been used more widely in forestry (Armstrong and Yule, 1978; Joyce and Spillman, 1978), tsetse control (Lee, 1977) and agricultural spraying (Joyce, 1975). Smaller, less expensive 'mini-Micronair' units are being introduced, while Parkin (1980) has studied the use of reticulated metal foam instead of wire gauze. Further studies on a rotary nozzle design for aircraft are in progress (Spillman, 1981) while spinning discs have been used on helicopters for tsetse control (Lee, Parker, Baldry and Molyneux, 1978). In the USA, the pulsed Microjet has been considered for use in aerial application (Yates, Akesson and Cowden, 1977). There has been interest in using remote-controlled aircraft, but considerable skill is needed to control the aircraft with sufficient accuracy (Johnstone, 1981). The low work capacity and high rate of depreciation make the system more expensive than conventional aircraft at present, but advances in track guidance could increase the prospects for such aircraft. Specialized equipment has been developed to apply small hollow polyethylene fibres containing pheromones: in particular, gossyplure has been applied aerially to cotton (Brooks, Doane and Haworth, 1979). The use of microencapsulated formulations of pheromones, however, enables standard spray-application equipment to be used. Improvements in aerial application of granules have led to the development of a new venturi spreader for Pawnee aircraft; not only does this new unit reduce drag and weight, but it is also easier to maintain (Bowker, 1981). O p e r a t o r protection Agricultural workers are most exposed to pesticide contamination when measuring out concentrated formulations and when mixing components (Akesson, Yates and Boos, 1977). In the USA there are now regulations requiring the use of closed systems for transfer of pesticides from containers to the sprayer, to avoid exposure of the operator. During application the main hazard is dermal contact and there is a risk of inhalation of small aerosol particles; appropriate protective clothing must therefore be worn. Lloyd (1979), reviewing developments in personal protection, has pointed out that protective clothing must be comfortable to wear if it is to be accepted by the operators, and that the adoption of authoritative standards would benefit both users and the manufacturers. The trend with tractors and self-propelled equipment is to have enclosed cabs with a powered filter system, but care must be taken to avoid contaminated clothing being taken into such cabs. Granule application

Comparatively little progress has been made with the application of granules: their use has been confined largely to certain highly toxic insecticides with systemic activity, and to certain herbicides. Baits have been used to control leaf-cutting ants (Lewis, 1972), but their wider use against other pests, such as cutworms, has been limited in many cases by the rapid reduction in attractiveness of the baits when rain-soaked. However, the development of polymers to provide some control of

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pesticide release, and the possibility of greater control of the size of granules, suggest that further development of application equipment would be worth while. Seed t r e a t m e n t Some weeds are particularly difficult to control with herbicides because the crop is also damaged if certain products are applied. In some cases, seed treatment of the crop with a herbicide protectant or safener, which acts as an antidote, provides a greater opportunity for selective control of the weeds. NA (1,8-naphthalic anhydride) has shown promise in pot experiments to protect maize when perfluidone or D P X 4189 were applied pre-emergence or diclofop-methyl was applied post-emergence (Blair, Parker and Kasasian, 1976; Parker, 1981). Further work is needed to explore the effectiveness of safeners under field conditions and to determine how long the protective effect persists. Methods of seed treatment have been reviewed by Jeffs and Tuppen (1978), who point out the necessity to apply a suitable formulation which will adhere to the seed and be distributed uniformly among them. The minimum amount of chemical to give adequate control of young seedlings has to adhere to the seed without causing any phytotoxicity. Seed treatment can be centralized at seed stores so greater use of this method of application to ensure better establishment of crops should be possible; for example, in the U K , seed merchants treat up to 95~o of the cereal seed with fungicides (Sly, 1972). The future Undoubtedly, over the next few years more attention will be paid to increasing the efficiency of pesticide application. With the improvements in application, greater use of selective pesticides (including the microbial insecticides such as Bacillus thuringiensis and a numbe r of baculoviruses) is expected in pest-management programmes. ~ s e o f pheromones to disrupt mating and reduce oviposition will probably be al6plicable to certain pest/crop situations, and there is the possibility of using pheromones formulated in conjunction with an insecticide, so that insects are attracted to the spray deposits. Many trends, such as the adoption of closed systems, quick-fit nozzles and fast high-clearance vehicles with low-pressure tyres, will continue to increase safety and cover areas quicker when climatic conditions are more favourable. In some areas, greatly improved ground-application systems may reduce the demand for aerial application. Changes in packaging, possibly with the availability of 'pallet spray tank loads' which eliminate the need for mixing chemicals on the farm, could also take place in areas with large-scale use of pesticides. In the tropics, manually operated knapsack sprayers will continue to be widely used but the trend towards U L V / C D A spraying will increase as more pesticides are suitably formulated and packaged for use by small-scale farmers. The reduction in power requirements is of fundamental importance for the Third World farmer, in view of increasing fuel and battery costs, but the most significant change in power supply will occur when the cost of harnessing solar energy is greatly reduced. Solar panels have been used successfully to power spinning-disc sprayers, and in the future it is possible that villages will be provided with a central large solar panel to recharge the batteries in the sprayers. Writing a review like this ten years ago, the upsurge of development in

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electrostatic spraying would have been very difficult to predict, following the waning of interest after demonstration of electrostatic equipment in the 1950s. Nevertheless, within a decade, a completely new type of spraying system, electrodynamic spraying, has been developed to farm-scale use. The potential for further exploitation of this new technique and other electrostatic systems, including the charging of hydraulic sprays (Figure 6), will undoubtedly increase during the 1980s. The miniaturization

FIGURE 6. Electrostatic spray being attracted to a plant. The water-based spray is produced from a standard hydraulic nozzle, the charge being subsequently applied. System developed and patented by National Institute of Agricultural Engineering, Silsoe, Bedford (NIAE photograph). of high-voltage generators, control of droplet size and trajectory by electrical forces, the minimal use of energy and the prospect of sprayers with microprocessor controls, all indicate that a major change in spray technology is under way, 100 years after knapsack sprayers were first used in the vineyards of France. In particular, the use of electrostatically charged droplets to minimize the risk of downwind drift will allow greater use of smaller aerosol droplets (which generally are biologically more active (Munthali, 1981)), and of much lower volumes of spray; however, this will necessitate more attention to the physical characteristics of formulations, especially the volatility of the carrier liquids. I f such a major change is to succeed, much needs to be done to evaluate new formulations, assess screening procedures and provide training at all levels to ensure better integration of pesticide use in crop protection. References AKESSON,N.B., YATES,H.E. ANDBOOS,S.W. (1977). Optimizingpesticidesafetywith closedmixing and handlingsystems.In: PesticideManagement and Insect Resistance, pp. 607-616. (ed. by D. L. Watson and A. W. Brown). New York: AcademicPress. ALLAN,J.R. McB. (1980). Developmentin monitoringand control systems for greater accuracyin spray application. In: British Crop Protection Council Monograph 24, pp. 201-213. Croydon: BCPC.

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ARMSTRONG,J.A. (1981). ULV/CDA optimum spray droplet size for control of the eastern spruce budworm in Canada, Outlook on Agriculture, 10, 327-332. ARMSTRONG,J.A. ANDYULE,W.N. (1978). The distribution of aerially applied spray deposits in spruce trees. Canadian Entomologist, 110, 1259-1267. ARNOLD,A.J. ANDPYE, B.J. (1980). Spray application with charged rotary atomisers. In: British Crop Protection Council Monograph 24, pp. 109-117. Croydon: BCPC. BALS, E.J. (1978). The reasons for CDA (controlled drop application). In: Proceedings, 1978 British Crop Protection Conference Weeds,pp. 659-666. Croydon: BCPC. BLAIR, A.M., PARKER,C. AND KASASIAN,L. (1976). Herbicide protectants and antidotes--a review. PANS, 22, 65-74. BOWKER, W.S. (1981). Aerial and ground application of solids: A comparison of opportunities, equipment and economics. Royal Aeronautical Society Symposium, 7 May. Unpublished. BROOKS,T.W., DOANE,C.C. ANDHAWORTH,J.K. (1979). Suppression ofPectinophora gossypiella with sex pheromones. In: Proceedings, 1979 British Crop Protection Conference- Pests and Diseases, pp. 853-866. Croydon: BCPC. BURGES,H.D. ANDJARRETT,P. (1979). Application and distribution of Bacillus thuringiensis for control of tomato moth in glasshouses. Proceedings, 1978 British Crop Protection Conference, pp. 433-439. Croydon: BCPC. BRANDENBURG,B.C. (1974). Raindrop-drift reduction nozzle. Transactions of the American Society of Agricultural Engineers, Paper 74-1595. CADOU,I. (1959). Une rampe portative individuelle pour la pulverisation ~ faible volume. Coton etfibres tropicales, 14, 47-50. CARLETON, J. AND BOUSE, L.F. (1980). Electrostatic spinner-nozzle for charging aerial sprays. Transactions of the American Society of Agricultural Engineers, 23, 1369-1373; 1378. COFFEE,R.A. (1979). Electrodynamic energy-a new approach to pesticide application. In: Proceedings, 1979 British Crop Protection Conference- Pests and Diseases, pp. 777-789. Croydon: BCPC. COFFEE,R.A. (1980). Electrodynamic spraying. In: British Crop Protection Council Monograph 24, pp. 95-107. Croydon: BCPC. COFFEE,R.A. (1981). Electrodynamic crop spraying. Outlook on Agriculture, 10, 350-356. COOKE,B.K., HERRINGTON,P.J., JONES,K.G. ANDMORGAN,N.A. (1977). Progress towards economical and precise top fruit spraying. In: Proceedings, 1977 British Crop Protection Conference- Pests and Diseases 2, p. 323. Croydon: BCPC. COOPER, A.S., FRASER,F., BURRILL,L.C. ANDDEUTSCH,A.E. (1981). Hand-held Wiping Devicesfor Herbicide Application. University of Oregon, Corvallis: International Plant Protection Centre. DALE, J.E. (1978). The rope wick applicator-a new method of applying glyphosate. Proceedings, Southern Weed Science Society, 31,322. DALE, J.E. (1979). A non-mechanical system of herbicide application with a rope wick. PANS, 25, 431-436. DOMBROWSKI,N. (1975). Improvements in and Relating to Liquid Spray Devices. British Patent No. 31000/75. ELLIOTT,J.G. (1980). Low volume, low drift and high speed - a great new opportunity. In: British Crop Protection Council Monograph 24, pp. 185-198. Croydon: BCPC. FULLERLEWIS, P. AND SYLVESTER,N.K. (1980). A comparative evaluation of a fan-assisted spinning disc ULV sprayer and a mistblower with ULV attachment. In: British Crop Protection Council Monograph 24, pp. 283-290. Croydon: BCPC. GARNETT, R.P. (1980). A low-volume herbicide applicator for tropical small-holder farmers. In: Proceedings, 1980 British Crop Protection Conference- Weeds, pp. 629-636. Croydon: BCPC. GIVELET, M.P. (1981). Electronic control systems in pesticide application machinery. Outlook on Agriculture, 10, 357-360. GRAHAM-BRYCE,I.J. (1977). Crop protection: a consideration of the effectiveness and disadvantages of current methods and of the scope for improvement. Philosophical Transactions of the Royal Society of London, Series B, 281, 163-179. GRIFFITHS,D.C., ARNOLD,A.J., CAYLEY,G., ETHERIDGE,P., PHILLIPS,F.T., PYE, B. ANDSCOTT, G.C. (1981). Biological effectiveness of spinning disc electrostatic sprayers. In: Proceedings, 1981 British Crop Protection Conference- Pests and Diseases, 2, 667-672. Croydon: BCPC. HEIJNE, C.G. (1978). A study of the effect of disc speed and flow rate on the performance of the 'Micron Battleship'. In: Proceedings, 1976 British Crop Protection Conference-Weeds, pp. 673-679. Croydon: BCPC. HERNANDEZ,S. (1978). Weeds and their control in Senegal. In: Weeds andtheir Controlin the Humidand

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