Growers warned: Spray in haste, regret at leisure

Author: Rachel Bowman | Date: 21 Jun 2013

Over head nozzle spraying water

Key Points

  • GRDC-funded research shows increased spraying capacity can improve spray results, if the machine is operated within appropriate limits.
  • Higher travel speeds have created the majority of issues associated with poor application.
  • Applicators and advisers need to be able to identify when application has contributed to reduced efficacy and be able to modify the application technique when required.

A growing trend among northern graingrowers to favour larger, wider spray rigs and self-propelled sprayers in order to cover ground more quickly carries the risk of reduced efficacy.

Spray application specialist, Bill Gordon, Bill Gordon Consulting says the risks include spray drift and shadowing.  

“When using a coarse spray quality, the larger droplets tend to hold their trajectory and faster travel speeds to increase the horizontal movement of larger droplets,” Mr Gordon says.

“This can lead to shadowing or misses of smaller weeds behind stubble, more spray depositing on one side of the target than the other, and poorer penetration into larger canopies.

“The impact of faster speed includes increased air movement past the nozzle which can narrow the effective sprayed width of each nozzle and lead to escape of smaller droplets from the pattern.

“Increased travel speed can also increase the wake affect around the machine and around the wheels, which can lead to poorer deposition of spray in and around the wheel tracks on many machines.”

This puts the onus on advisers, growers and spray operators to be informed and conscious of the impacts, he says.

“The greatest temptation for operators of self-propelled sprayers is to travel at higher speeds than they may have previously considered, simply because their machines allow them to,” Mr Gordon says.

“Increased speed can produce effects at the nozzle, at the target, and around the machine itself.”

Mr Gordon says increased spraying capacity is positive when growers aim to improve the timeliness of sprays but comes with an increase in the risk of off target damage if spraying takes place with the wrong set up or during unsuitable weather conditions.

“Many operators and advisers don’t fully understand the risks associated with spraying during the presence of surface temperature inversions, which occur on most nights,” he said.

“This should be considered before an application takes place.”

Mr Gordon told growers and advisers at the Grains Research and Development Corporation (GRDC) Goondiwindi Research Update recently the other major trend has been towards air induction nozzles, typically producing larger droplets.

“Both of these trends have resulted in both positive and negative effects on the spray results, depending on what practices are used to increase that capacity,” he said.

“We should know all what to look for in relation to application technique when assessing the outcomes of a spray job, so that we can make informed decisions about what parameters may need to be adjusted.”

GRDC has funded research into best practice spray application, including droplet size and nozzle selection.

Mr Gordon says advisers should include the following in their written recommendations:

  • target species and situation
  • product trade names, active ingredients and rate of active to be applied
  • mixing order and water quality requirements
  • minimum legal spray quality
  • minimum and maximum application volumes
  • advice regarding no spray zones (such as a general statement to read the label and adhere to all restraints)
  • a general statement regarding risk of spray drift, sensitive areas, plant back, re-entry and withholding periods
  • an expiry date for the recommendation

“Any other information about application technique, such as nozzle selection, pressure, speed and rate controller settings should be discussed pre-season, where the operator and the adviser develop a series of spray plans, so both on the same page during the season,” he said.


Caption: GRDC-funded research shows increased spraying capacity can improve spray results, if the machine is operated within appropriate limits.

Contact Details

For Interviews

Bill Gordon Consulting
0429 976 565


Rachel Bowman, Senior Consultant, Cox Inall Communications
07 3846 4380 / 0412 290 673

GRDC Project Code BGC00002

Region North