Crop Desiccation with Minimum Spray Drift1

Chemical desiccation with Regione (diquat) of oilseed crops prior to harvesting is now a well established farming practice. The many varied practical (and economic) advantages give the farmer more flexibility and control in planning his operations at a particularly busy time of year. However, desiccants are not selective of green plant tissue, so it is important that the spray is confined to the target crop. Spray drift is not normally a problem with ground spraying, but with aerial application particular care in the selection of equipment, flying technique, and climatic conditions is essential. This is particularly important when desiccating early maturing crops, such as oil-seed rape, when other crops, for example sugar beet and maize, are still green and growing. The potential spray drift risk can be reduced by planting similar crops in large blocks rather than in fragmented strips throughout the farm. By restricting the length of spray boom on the aircraft, using efficient diaphragm shut-off nozzles angled rearwards to the airstream, fitted with nozzles such as spraying Systems D8 or 10 with 46 or 56 swirl plates operating at maximum pressure of 2 bar, much of the drift hazard resulting from the equipment can be reduced. It is essential that the spray is turned on/off only in level flight and that the height of the spray boom above the top of the crop is less than 2.5 m. Spraying should only be carried out in wind speeds of 1-4 m/s and never under temperature inversion conditions. Large helicopters should only be used discriminately in very large areas of crop.