Ground Cover Supplement : GC Supplement - Spray application 2016
8 Drift management However, moving to very large droplet sizes, such as an extremely coarse (XC) spray quality, can create situations where efficacy is reduced. These include: ¢ using contact-type products; ¢ using low application volumes; ¢ targeting very small weeds; ¢ spraying into heavy stubbles or dense crop canopies; and ¢ spraying at higher speeds. If spray operators intend to use a coarser spray quality than recommended on the label, they should seek trial data to support this use. If data is not available, operators should spray small test strips to compare the larger spray droplet sizes to their regular nozzle set- up and carefully evaluate the control obtained. Farm advisers or agronomists can assist in evaluating the efficacy. BOOM HEIGHT Boom height above the target is critical to ensuring an even overlap of nozzle spray patterns. For most broadacre spraying, the aim is to achieve a double overlap of the spray patterns from each nozzle. Double overlap occurs when the outer edge of the spray patterns arrive at the target area in alignment with the adjacent nozzle. Wider fan angles can allow for lower boom heights, but the trade- off will be an increase in drift-prone droplets produced compared with fans of the same type and orifice size. Increasing the boom height above what is required to achieve the overlap will increase the amount of chemical that remains in the air, because the smaller drift-prone droplets lose their downward velocity very quickly. Research has shown that when using the same nozzle type at the same pressure, increasing boom height from 50 centimetres to a height of 70cm above the target can increase the amount of drift-prone droplets by as much as four times. An increase in boom height from 50cm to higher than 100cm can result in a 10-fold increase in the amount of drift-prone droplets from some nozzles. The amount of increase in drift potential is related to the size of the droplets, their initial velocity and the rate at which they slow down. PRODUCT AND FORMULATION CHOICE The choice of active ingredient and formulation can influence the droplet sizes produced by a nozzle, as well as the level of damage that may occur. An operator can reduce drift or potential damage by: ¢ substituting the product: in some situations an alternative active ingredient may have a lower impact on sensitive areas -- for example, using 2-methyl-4-chlorophenoxyacetic acid (MCPA) in place of 2,4-D where it will provide an appropriate level of control on the target weeds; and ¢ selecting a different formulation type: for example, choosing a salt- based product in place of an ester-based formulation, or choosing an emulsion-type formulation over an aqueous concentrate. Product labels with downwind buffers or no-spray zones provide a useful basis for comparing products to see which present a lower risk to a sensitive area. RATE OF PRODUCT USED Robust product rates are important for control and to minimise resistance. However, the rate of product can also influence the level of damage that may occur if the product moves away from the target area. The rate of product applied per hectare can influence: ¢ the total amount of the active ingredient available to move off target; ¢ the concentration of the active ingredient within each droplet; and ¢ the concentration of adjuvants and additives within the spray solution that can affect droplet size and drift potential. Higher product rates increase the amount of active ingredient released into the environment. When more active ingredient is released, a greater buffer distance downwind is required for sufficient dilution and reduced concentration of deposited droplets. The total volume of spray product should be adjusted accordingly. If water rates are not increased, droplets will contain a higher concentration of active ingredient and can cause increased damage if they land on a sensitive area or crop. Lowering water rates has a similar effect on droplet concentration as increasing product rates, as this produces more concentrated droplets. Increasing the concentration of the active ingredients also increases the concentration of other Many communities take spray drift very seriously. Drift-management strategies become critical in areas where sensitive crops such as grapes and cotton are grown. PHOTO: SOUTHERN PRECISION PHOTO: BILL GORDON A Crop Stalker 10-metre shielded sprayer. Shielded sprayers can reduce spray drift by more than 90 per cent and help prevent spray droplets from depositing onto the crop.
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