Avoid spray drift by recognising unsafe conditions

Date: 02 Dec 2011

Surface temperature inversion. Photo Bill Gordon.

Avoid spray drift by recognising unsafe conditions

Grain growers are being encouraged to avoid pesticide spray drift by developing an understanding of weather conditions conducive to spray drift.

Recognition of conditions that lead to a surface temperature inversion is particularly important as the potential for spray drift is high when this occurs, according to industry authorities.

Spray consultant Bill Gordon, whose work is supported by the Grains Research and Development Corporation (GRDC), says surface temperature inversions commonly develop overnight, when the ground loses heat and the low-level air cools.

“This results in air temperature increasing with height and the temperature profile is said to be inverted. When this occurs close to the ground it is called a surface temperature inversion,” said Mr Gordon, of Bill Gordon Consulting, Lawrence (NSW).

“Unlike warm air that rises, cool air is dense and remains at the surface. Sprays applied in these conditions can become trapped in this cool air layer.

“Once trapped, unpredictable air movement can transport droplets away from the target area.”

Meteorologist Graeme Tepper, of MicroMeteorology Research and Educational Services, said when surface inversions exist pesticides in the air can move long distances at high concentrations near the surface and adversely impact non-target receptors, often in directions and locations that could not be estimated from general weather patterns.

“The scientific method for detecting a surface temperature inversion requires the accurate measurement of the air temperature close to the ground and at a height of at least 10 metres,” Mr Tepper said. “On-farm, this is usually not practical, so most spray applicators must rely on visual clues.”

Mr Tepper said a surface temperature inversion does exist if mist, fog, dew or a frost occur, and smoke or dust hangs in the air and moves sideways, just above the surface. Other clues include cumulus clouds that have built up during the day collapsing towards evening, sounds becoming very clear at night and aromas becoming more distinct at night.

To assist growers with understanding how and when a surface temperature inversion occurs, the GRDC, with assistance from Mr Gordon and Mr Tepper, has developed a Surface Temperature Inversions and Spraying Fact Sheet.

The Fact Sheet is included in the November-December edition of GRDC’s Ground Cover magazine and can also be viewed and downloaded via www.grdc.com.au/GRDC-FS-sprayinversions.

Research supported by the GRDC is further investigating the development
and implications of temperature inversions in relation to spray application.

ENDS

Caption: Under a surface temperature inversion air can separate into very stable layers (laminates) that can concentrate and transport airborne pesticides. Photo courtesy Bill Gordon.

• Media requiring further information can contact Bill Gordon on 0429 976565 or Graeme Tepper on 0429 309508

• GRDC project codes: BGC00001, MRE 00001

• This media release and other media products are available via www.grdc.com.au/media

GRDC Project Code BGC00001, MRE00001