Ten tips to reduce spray drift

Grains Research and Development Corporation (GRDC) Senior Manager Crop Protection Ken Young said growers were committed to setting up their spray equipment and using chemicals in the most effective and efficient way to control weeds, diseases and pests.

“Inputs like herbicides equate to around 30 per cent of growers’ input costs so they are very motivated when it comes to best practice chemical management,” Dr Young said.

“Growers want applications to be on-target, applied safely and used in the most effective way on-farm.”

Spray application expert Bill Gordon, the author of several Grains Research and Development Corporation (GRDC) fact sheets on spray application best practice said there were several steps growers or operators could take to minimise off-target movement of spray. 

“Growers can control the when, where, how and what of spray application, the only thing they really can’t control is the weather and then they need to access reliable forecast information so they only apply products at times of lowest risk,” Mr Gordon said.

He said early storms, warm weather, large areas of fallow and plans for summer planting meant many Queensland and northern New South Wales growers and spray operators were currently planning spray applications.

“It is important growers control weeds early in fallow and ahead of summer planting, but it is equally important that they do it safely and with minimum risk.”

Mr Gordon said there were simple steps growers and spray operators could take to apply chemicals safely.

Choose products carefully, this includes the choice of active ingredient, the formulation type and the adjuvant used. 

Understand the products mode of action and coverage requirements on the target– read the crop protection product label for guidance on spray quality, buffer (no-spray) zones and wind speed requirements. 

Select the coarsest spray quality that will provide an acceptable level of control. Be prepared to increase application volumes when coarser spray qualities are used, or when the delta T value approaches 10 to 12. Use water sensitive paper and the SnapCard app to assess the impact of coarser spray qualities on coverage at the target. 

 Always expect surface temperature inversions will form later in the day, as sunset approaches, and they are likely to persist overnight and beyond sunrise on many occasions. If the spray operator cannot determine that an inversion is not present, then no spraying should occur. 

Use weather forecasting information to plan the application. Bureau of Meteorology (BOM) meteograms and forecasting websites can provide information on likely wind speed and direction for 5 to 7 days in advance of the intended day of spraying. Pay close attention to variations between predicted maximum and minimum temperatures above 5 to 7 degrees Celsius, delta T values below 2, low overnight wind speeds (less than 11 km/h) and predictions of dew or frost as these all indicate the likely presence of a surface inversion.

Only start spraying after the sun has risen more than 20 degrees above the horizon and the wind speed has been above 4 to 5 km/h for more than 20 to 30 minutes, with a clear direction that is away from adjacent sensitive areas. 

Set the boom height to achieve double overlap of the spray patterns. With a 110 degree nozzle using a 50cm nozzle spacing, this is 50cm above the top of the stubble or crop canopy. Boom height and stability is critical, use height control systems for wider booms or reduce the spraying speed to avoid boom bounce. 

 Avoid high spraying speeds, particularly when ground cover is minimal. Spraying speeds above 16 to 18 km/h with trailing rigs, and above 20 to 22 km/h with self-propelled sprayers greatly increase losses due to affects at the nozzle and the aerodynamics of the machine. 

Be prepared to leave unsprayed buffers when the label requires, or when the wind direction is towards sensitive areas. For ground application of non-volatile products using a coarse spray quality (or larger) during daylight hours and wind speeds between 3 and 20 km/h a 300m downwind buffer is generally sufficient, however you should always refer to the spray drift restraints on the product label. Smaller spray qualities will require larger buffers. 

Continually monitor the weather conditions at the site of application. Always measure and record the wind speed, wind direction, temperature and relative humidity at the start of spraying and at the end of every tank, according to the label requirements. Label no-spray zones and downwind buffer distances are based on wind measurements at 2m above the ground.