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  • Jess Bennett & Rob Sluggett

Inversion season is here!

Updated: Jun 21, 2023

Were you aware that as we come into winter, most early mornings are unsuitable for spraying? Pretty much illegal, in fact! Current regulations prohibit spraying when surface temperature inversions exist.

What is an "inversion" in relation to spraying? A surface temperature inversion is where the air near ground level becomes cooler than the higher air. Cooler air is more dense, so it stays near the surface. As this air warms during the day, it rises and moves with the prevailing winds. Small droplets from spraying suspended in this cool air with move with it. It is possible for these droplets to be moved over 30km from the field sprayed. Think about the huge number of sensitive areas within 30km of your farm. Towns, schools, creeks, sensitive crops, even your house roof where you catch drinking water. Spraying should NEVER be undertaken when there is an inversion present.

Most agricultural chemical labels instruct that spraying should only be done with a wind speed above 3km per hour (typically 3 to 20km/h). At less than that, there is a very good chance that a surface temperature inversion may be present.

What can you do?

  • Sleep in. In the morning, wait until wind speed picks up above 3 to 5km/h before commencing spraying. Know when to stop. In the late afternoon, spraying will normally need to finish as winds drop to 7km/h or lower. This is to ensure spray deposit before cool conditions set in.

  • Pay attention. Measure and monitor weather conditions at the field of application.

  • Upgrade your nozzles. Most sugar industry spray rigs are running standard air induction nozzles that are producing around 15% of the spray volume as driftable fines (droplets smaller than 150 microns). These are the droplets that hang in the air longer and move with inversions. Changing to the latest technology low drift nozzles that allow safer spraying in higher wind speeds during the day is the best approach. If you feel you need to spray when the wind speed is low, you are running the wrong nozzles!

We can assist! Farmacist has industry-leading specialists available to support the best choice of nozzles and sprayer setup for your conditions. Funding support may be available to assist with any upgrades. Please get in touch with your local Farmacist agronomist today.


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