Target spray volume

A combination of techniques is typically used to verify the accuracy and precision of agrochemical applications to soil. For example, the catch-back method or passtime method is typically used in conjunction with analytical results from application verification monitors to confirm proper application. The catch-back method involves measuring the spray solution volume before and after application to double check that the desired volume of test solution was actually applied to the test plots. Experienced applicators are often able to apply within 2% of the targeted spray volume. 

Target the minimum recommended spray volume per acre. The nozzle configuration should be adjusted to fit the canopy at the time of application, which is normal agricultural practice. The application sprayer should be calibrated prior to treatment. Calibration records should be maintained and submitted as raw data. Applications should be made within 1 h of mixing and applied at a time with little or no wind. The applications should be made when leaves are dry. All application parameters must be recorded. The following list gives example data collection from application ... 

Although wide drop-size distributions can sometimes be an advantage (Hislop, 1983) the large numbers of small drops produced in hydraulic nozzle sprays can result in spray drift and inadequate targeting (Miller, 1993). Rotary atomisers (Bals, 1975) can reduce the breadth of drop-size distributions and provide a more targeted size distribution. They have not been widely adopted in broad-acre ground crops, because their spray volumes and drop trajectories often cause control difficulties, but they have found some acceptance in orchard sprayers. 

In agricultural spraying, one of the biggest concerns is the drifting of small droplets. Drifting sprays not only lead to waste and environment problems, but also could endanger other nearby crops. Droplets smaller than 150 p.m can be easily blown away from the intended target area by a cross wind. A typical herbicide atomizer produces a spray with 15—20% of the Hquid volume contained in droplets less than 150 p.m. Atomizer improvements must be made so that the spray contains a narrow droplet size distribution with Hquid volume less than 5% contributed by the smaller droplets. 

Figure 3 shows data for a spinner atomizer in a 110 mi/hr airstream. The vmd is 140 microns, the % volume in drops less than 122 microns is now 24% while the relative span has increased to 1.23. It is this tremendous increase of drops (less than 122 microns dia.) from 2.0% for the 300 microns spray to 24% for the 150 microns spray that is a potential source of trouble from airborne transport of these small drops. These are carried away from the treatment area and a potential exists for contact with humans and animals as well as unwanted deposit on non-target crops. These small drops have been found at distances of several miles from the actual applications (5). If the material being released is of low toxicity, or in a remote area, the problem is not serious. But for high toxicity materials the 24% loss which is not controlled, poses a serious problem. 

During recent years, the tendency to apply smaller and smaller volumes of spray per hectare has necessitated the use of small drops to maintain adequate distribution. However, the size of the drops cannot be reduced indefinitely without affecting their ability to impact on the target, and in any case, as the drop size is reduced, the tendency of the spray to drift from the target is increased. Thus, there is an optimum drop size for most spraying operations which represents the smallest drop size consistent with satisfactory impact efficiency. To determine this optimum size for any particular application, one must take into account the mode of action of the toxicant, the nature of the crop, the type of spray equipment, and the volume of spray to be applied. 

Technology once primarily adopted for herbicide application is now being increasingly used for low-volume (LV) insecticide application in the Australian cotton industry, in an attempt to reduce the potential for the off-target movement of sprays, and preserve the flexibility and use of productive and efficient ULV techniques. 

The most important parameters that determine which of the above stages is reached are the mass (volume) of the droplet, its velocity in flight and the distance between the spray nozzle and the target surface, the difference between the surface energy of the droplet in flight, Eq, and its surface energy after impact, and displacement of air between the droplet and the leaf... 

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