2,4-D herbicides are used for the control of broadleaf weeds in pastures and crops. However, because some formulations of 2,4-D are quite volatile, there is a risk that vapour may drift off-target. This poses a potential risk to highly susceptible non-target crops (e.g. grape vines, vegetables, glasshouse crops and poppies). Some crops have been damaged by 2,4-D herbicides applied up to 10 kilometres away.
Crops, particularly grape vines, are most susceptible during the growing season. High temperatures during this period or spraying during a temperature inversion also increases the likelihood of vapour drift. A good explanation of how temperature inversions occur and a video showing how smoke drifts under surface inversion conditions, can be found at https://sprayers101.com/surface-inversions/ (courtesy of www.sprayers101.com). Signs of temperature inversions that indicate that there is a significant risk of droplet/vapour drift over large distances are listed below.
- Large temperature swings between daytime and the previous night.
- Calm (e.g. less than 3 km/h wind) and clear conditions when the sun is low.
- Wind speed constantly less than 11km/hr in the evening and overnight (11kph required to disperse an inversion layer).
- Intense high pressure systems (usually associated with clear skies) and low humidity where you intend to spray.
- Dew or frost indicating cooler air near the ground.
- Smoke or dust hanging in the air or moving laterally.
- Odours travelling large distances and seeming more intense.
- Daytime cumulus clouds collapse toward the evening.
- Overnight cloud cover is 25% or less.
In August 2013, the Australian Pesticides and Veterinary Medicines Authority (APVMA) cancelled the registration of 11 high volatile 2,4-D ester products as spraying these products resulted in vapour drift over several kilometres. Although the cancellation of these high volatile 2,4-D products resulted in fewer reports of spray/vapour drift from 2,4-D, it was not eliminated.
Tasmania has a requirement for users of 2,4-D to apply for a permit for use during the period 15 September to 15 April to try and minimise the risk. Other states have taken a similar approach. However, ongoing reports of vapour drift prompted the APVMA to review the use of 2,4-D and on the 3rd October 2018, all labels for 2,4-D were suspended and new 2,4-D label instructions were introduced.
The new instructions for use include:
- a mandatory requirement not to spray in inversion conditions and additional information on recognising inversion conditions
- downwind mandatory no spray zones for both aquatic and terrestrial off target vegetation (including sensitive crops, gardens, landscaping vegetation, protected native vegetation or protected animal habitat)
- a mandatory requirement to use nozzles producing droplets no smaller than the Very Coarse spray quality category
- mandatory record keeping requirements, and
- advisory statements about spray application over summer.
Users must comply with all label requirements including the specific records that are additional to those required under the Agricultural and Veterinary Chemicals (Control of Use) Act 1995.
The new requirements do not change or restrict other aspects of the currently approved use patterns and should not affect availability of the product.
Application Form - 2,4-D Agricultural Spraying Permit (48Kb)
Permits will only be issued after consideration of factors such as:
- the distance between the target area and susceptible crops,
- application method e.g. boom spray, spot spray or wiper application,
- availability of alternative herbicides or weed control methods,
- whether the application could have been made earlier (i.e. before 15 September).
A charge will be made for site inspections that may be necessary before a permit can be issued. Permit application forms can be obtained from the Department of Primary Industries, Parks, Water and Environment offices and website (PDF format above).
It is recommended that if you need to use 2,4-D herbicides to control weeds such as thistles and ragwort, you should apply them before 15 September. This will reduce the risk of off-target damage and also avoid the need to get a permit. It is also likely that applications at this time will provide more effective weed control with less pasture damage.
You should note however, that 2,4-D drift can occur at any time of the year. As with any other herbicide application, you must ensure that you take the necessary measures to reduce the risk of off-target damage.