Avoiding Spray Drift

Using phenoxy’s safely

Peter Willmott and David StephensonPIRSA Biosecurity – Rural Chemicals

Summer Weed Spraying

• Rainfall on 12-14 December germinated annual weeds and freshened perennials

• Around 90,000 ha sprayed from late December to late January 2009 within 30km of Clare Valley

• 2,4-D ester, amine, triclopyr, glyphosate

• Damage to vines throughout Clare Valley

Extent of damage

Purchase of chemicals

Label Requirements for 2,4-D

For all 2,4-D• DO NOT use unless wind speed is more than 3 kilometres per hour

and less than 15 kilometres per hour as measured at the application site.

• DO NOT apply with smaller than coarse to very coarse spray droplets according to the ASAE S572 definition for standard nozzles.

Additional requirements for HVE• DO NOT apply this product between 1 September and 30 April. Use

only within the SPRAY WINDOW between 1 May and 31 August.• DO NOT apply this product by air.• Within 24 hours of completing a 2,4-D ethyl, butyl or isobutyl ester

application all users must make and keep a record of each application.

Recommended conditions

Buffer distances

Spraying near sensitive crops should occur only when the wind is blowing positively away from the crop, and not closer than– 100m for amine

– 1.5km for LV ester.

These distances can be reduced to 20m and 100m in winter

Methods of Drift

• ‘Classical’ spray drift

• Vapour drift

• Microdroplet drift

Vapour Drift

• HVE (eg Estercide 800) volatilises at 22°C• LVE (eg Estercide Xtra 680) volatilises at 28°C• Triclopyr similar to LVE• Amines are essentially non volatile

• Volatilisation occurs if the temperature rises above the threshold after application for at least the next day.

Microdroplet drift

• Microdroplets are the very fine droplets (mist) produced by all nozzles

• In calm conditions, the droplet can remain suspended in the air

• In low humidity or at higher temperatures, these droplets can evaporate, with the active suspended in the air

• In unsettled conditions, the droplet can rise on warm air and travel on the wind

Spraying conditions

• Maximum forecast temperature• Temperature at time of application• Relative humidity (delta T)• Wind speed at time of application• Wind shift and variability during application• Temperature inversions• Spray quality – nozzle size• Boom height (speed)

Observations at Clare BOM

Opportunities to spray

Key message

there are more opportunities to use amine than LVE

LVE Amine

1am 36% 80%

6am 29% 75%

9am 20% 43%

3pm 0% 0%

Consistent wind

3 January 2009

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Calm conditions/inversion

6 January 2009

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Variable wind/possible inversion

4 January 2009

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General Duty

• The Act provides for a General Duty that chemical users must take all reasonable and practical measures to not cause harm to land, plants, livestock or people through their use of chemicals, particularly through off-target damage

Future actions

• Label changes

• Education

• Air monitoring

• Record keeping