SPRAY DRIFT - Keep the spray on the weeds

 

Off-target spray drift is a significant issue for summer cropping in Australia, causing injury and economic damage to a range of crops and the environment. It is important that chemical users "keep the spray on the weeds" not only from an efficacy standpoint but also to prevent off-target injury to crops.

Spraying agricultural chemicals, whether from the ground or the air, needs to be properly planned and carefully monitored and executed, to maximise effectiveness and to minimise the risk of off-target chemical movement.

The environmental conditions in summer are conducive to inversion conditions which can lead to large plumes of chemicals moving considerable distances off-target. Many of the causes of off-target spray drift are a result of:

  • Poor equipment set up

  • Product selection of high volatility products

  • Application in environmental conditions which are not suitable

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WHAT IS AN INVERSION?

Typical vertical temperature profiles for a point in time during the night and day. The day profile typically cools with height and the night profile typically warms with height to a depth which constitutes the surface temperature inversion layer. The point where the temperature stops increasing is the top of the surface temperature inversion layer.

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TRAINING AND ACCREDITATION
• A current chemical user accreditation certificate (AQF 3) is required by any operators applying chemicals in NSW.

• All spray contractors and staff need to be licenced by EPA or Biosecurity Queensland.

 

NEIGHBOUR COMMUNICATION 
• It is good practice to discuss cropping intentions with neighbours prior to each season.

• Keep abreast of sensitive crops at https://crop.satamap.com.au.

 

RECORD KEEPING
• Legislation requires accurate records to be made.

• Records need to be kept for 3 years in NSW and 2 years in Queensland. 

• Check labels for any extra records that need to be kept in addition to state requirements.

 

PRODUCT CHOICE
• All products can drift.

• Different products have different volatility.

• Choose products which are fit for purpose.

• Be aware of the effects of mix partners and adjuvants on volatility and drift potential.

 

APPLICATION TIMING
• See 24 hour risk profile for summer spraying diagram.

• Expect an inversion every night They commonly occur one or two hours before sunset and persist through the night until one or two hours after sunrise.

WIND SPEED
• Only apply at wind speeds between 3-15km/h (day time wind speed only).

• Check label for mandatory no spray zones.

• Preferably apply when wind is blowing away from sensitive areas or crops.

• Monitor wind direction and speed at the site of application, before, during and completion of each application.

WATER VOLUME
• Ground rigs - a minimum of 60 L/ha.

• Use higher water volumes to ensure good efficacy.

DROPLET SIZE
• Boom sprayers - a minimum spray quality of Very Coarse is mandatory. See next dot point.

NOZZLE CHOICE & PRESSURE
• You must use a nozzle that produces Very Coarse (VC) spray quality.

• Between 1 Oct and 15 Apr use Extra Coarse (EC) spray quality.

BOOM HEIGHT
• No more than 0.5m above target or false target (for 110° fan angle).

APPLICATION SPEED
• Aim to eliminate boom movement.

• As most rigs are rate controlled, utilise speed to a minimum of Very Coarse spray quality. Speeds above 21 km/h reduce efficacy and increase drift potential.

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