Spraying, Spray Drift and Off-target Damage
Calibration and Preparation of Boom Sprayers
Using Knapsack Sprayers and Compression Sprayers
Spray drift and off-target damage
Spray drift is the most common cause of off-target chemical movement. As an agricultural chemical user, you must take care to prevent spray drift.
It is an offence to undertake agricultural spraying which:
- injures any plants or stock outside of the target area
- injures any land outside the target area so that growing plants, or keeping stock on that land would result in contamination, or
- is likely to contaminate any agricultural produce derived from plants or stock outside the target area.
A combination of various factors can contribute to spray drift, including wind speed and direction, temperature, boom height, droplet size and the volatility of the chemical.
Chemical users should also be aware of the higher potential of certain herbicide formulations to drift and cause off-target damage.
Spray maps and other information given to spray contractors should be accurate and contain all the relevant details.
Volatile vapour drift
Most chemical users are aware that certain phenoxy herbicide groups (e.g. 2,4-D, MCPA, triclopyr and picloram) are available as amine, salt, or ester formulations. Knowing the characteristics of the phenoxy herbicide group and formulations is important when the intended use is in the vicinity of a susceptible broadleaf crop, as they can cause unintentional damage to susceptible crops, even when used at extremely low levels.
While amine formulations can drift as droplets only, ester formulations have the ability to produce vapour that can drift significant distances from the target area. Many valuable crops including vines, cucurbits (melons, pumpkins and zucchinis), tomatoes and fruit trees are highly susceptible to ester formulations of 2,4-D MCPA and triclopyr.
The volatility of ester formulations is significantly greater than other formulations because they have the ability to volatilise after application under certain conditions, and drift as a vapour for many kilometres, damaging non-target crops. This combination makes these herbicides a high risk option.
To determine whether a herbicide is an ester formulation, read the active constituent on the product label. If ‘ester’ appears anywhere in the active constituent name, the product is classed as an ester formulation. Some ester products are named Low Volatile Ester (LVE) formulations. These products are still classed as esters and have the potential to produce vapour drift.
Below is an example of a product label. One of the active constituents in this product is MCPA present as an ester. Therefore this product is a ‘restricted use’ chemical and an ester formulation.
Restrictions for using certain ester herbicides
Anyone who uses ester formulations of 2,4-D, 2,4-DB, MCPA or triclopyr (i.e. ‘restricted use’ chemicals) in Victoria must hold a valid Agricultural Chemical User Permit (ACUP) or be working under the direct supervision of an ACUP holder.
‘Restricted use’ chemicals are agricultural chemical products that:
- are Schedule 7 Poisons (Dangerous Poisons)
- contain atrazine, metham sodium or ester formulations of 2,4-D, 2,4-DB, MCPA or triclopyr.
In addition, the use of ester herbicides is restricted in Agricultural Chemical Control Areas (ACCA) when they are in operation. This is to provide protection for valuable crops during their growing seasons.
It is compulsory to make specified records within 48 hours of using an agricultural chemical product, and keep these records for a period of two years. This applies to all agricultural chemicals used, including poison baits used for pest animal control.
Plan your spray job
When planning a spray job, the sprayer operator must check for susceptible plants, animals and/or land in the vicinity of the target, and put strategies in place to ensure spray does not leave the target area. For example, it may be necessary in some circumstances to leave an unsprayed buffer next to a susceptible crop to ensure off-target spray drift does not occur, and then come back and spray the buffer with a different breeze another day.
It is also important the sprayer operator keeps an eye on the conditions throughout the spraying operation, as it is not uncommon for conditions to change throughout the day, and conditions that may have been acceptable at the start may not be later.
Off-Target Spray Drift Uncontrolled Unnecessary Unacceptable
Top 10 spraying tips
Buffer zones and vegetative barriers
Buffer zones and vegetative barriers are valuable tools that can be used to reduce the potential for spray drift when applying agricultural chemicals.
A buffer zone is an area around a sensitive area in which agricultural chemicals should not be applied. The presence of a buffer zone allows spray drift to settle out of the air stream as it travels across the buffer zone before reaching the sensitive area. Prior to undertaking spraying, you should assess the risks and determine an appropriate buffer zone, as it will change from paddock to paddock and from year to year.
The required distance of a buffer zone will vary a great deal and may be different from day to day as you must take into account:
- The product you are using, some require buffer to be used in order to legally use the product. When using products that specify a required buffer distance it is important to make a note that this was observed when making a record of use.
- The type of application equipment as a boom sprayer applying a COARSE droplet size is less prone to drift than a mister applying a FINE droplet size.
- The nature of the sensitive area you are trying to protect as different distances may be required for crops compared to residential housing etc.
- The environmental conditions on the day, especially the wind direction and speed.
A vegetative barrier refers to a row of trees, shrubs or tall grasses that has been planted in strategic lines to reduce the extent of spray drift. They are effective in reducing spray drift by filtering out spray droplets in the air as it passes through their foliage.
A vegetative buffer will not reduce vapour drift or odours associated with spray drift.
A good vegetative buffer should be:
- taller than the target plants or the spray unit used for chemical application
- trees or other plants with foliage that allows sufficient air movement (50% porosity)
- plants with long, thin, rough foliage which are more suitable as a vegetative barrier.
Examples of suitable plants include:
- casuarina or sheoak (Allocasuarina spp.)
- hybrid willows (evergreen only)
- rye corn
- sorghum
- bottlebrush (Callistemon spp.)
- tea tree (Leptospermum spp.).
Vegetative buffers are desirable:
- along crop or property boundaries
- next to sensitive areas (e.g. susceptible crops, residential areas, hospitals etc
- along sprinkler rows, bordering waterways
- between blocks or paddocks.
It is important to be aware of the following limitations:
- They are not a substitute for good agricultural practice (GAP). If it is too windy then you should not be spraying as either a buffer zone or a vegetative barrier may not be able to stop drift. They are intended to reduce the risk spraying in nearly ideal conditions and help protect against unpredictable gusts.
- They will not stop vapour drift or odour occurring, this is purely a consequence of the product itself and the weather conditions.
Using Buffer Zones and Vegetative Barriers to Reduce Spray Drift
Weather conditions and drift
As a chemical user, you have a legal obligation to avoid spray drift damage and to ensure that the chemicals you apply stay within the target area.
While wind plays a key role in the risk of droplet drift and is one important factor in volatile vapour drift, volatile vapour drift can occur under what may seem as ‘ideal’ conditions.
Some people think that a still or dead calm day is ideal for spraying. A still, dead calm day, particularly in autumn or spring might indicate the presence of an inversion in the atmosphere. Spraying volatile herbicides such as esters under inversion conditions is a recipe for disaster.
Volatile vapours can travel many kilometres under an inversion, and there is no way of predicting where they may land and cause damage.
Care should also be taken to avoid spraying when extreme temperatures are predicted, especially when using ester formulations. Remember, it is still possible for volatile vapours to form days after their application.
Chemical users should avoid spraying in the following conditions:
- winds less than 3 km/h and greater than 15 km/h for ground-based application, note that some products may require more specific wind conditions
- when winds are blowing towards herbicide sensitive crops, which may be damaged/contaminated by spray drift
- when winds are blowing towards sensitive services (e.g. school)
- unpredictable sea breezes and other winds caused by heating and cooling of the land throughout the day
- visible dust movement
- inversion layer at an altitude of less than 100 m
- still and frosty conditions
- excessively low (dry) or high (humid) relative humidity
- excessively low or high temperatures
- rain is forecast.
The following tools can be used to estimate or measure wind speed and direction:
- anemometers (available in small hand-held electronic meters)
- wind speed chart
- weather station
- windsock
- smoke generator.
Guide to Estimating Wind Speeds - For Spraying Agricultural Chemicals
Reporting Spray Drift of Agricultural Chemicals
In the event that your crops, stock, or land has been subjected to spray drift caused by agricultural chemicals, you need to immediately report the incident to the DPI Chemical Standards Officer in your area. Chemical Standards Officer details are listed under ‘Contact/services available from DPI’. You may be advised by the Chemical Standards Officer to take samples of the affected produce, or to take digital photo’s etc as an aid to any potential investigation that is subsequently launched. If an investigation is launched, you will be asked to provide a witness statement and be prepared to give evidence in court.
Public Health Issues
Individuals with public health concerns relating to agricultural chemical spray drift should contact the Environmental Health Officer at their local municipal council. Whenever a health concern is raised it is also essential to discuss the issue with a Doctor as soon as possible.
For emergencies, customers should contact the Victorian Poisons Information Centre, open 24 hours, 7 days a week on 13 11 26.
Occupational Health and Safety
In the event of workplace occupational health and safety issues, contact your nearest Worksafe agency. Worksafe contact phone numbers: 1800 136 089 (Toll Free) or (03) 9641 1444.
Environmental Issues:
For environmental enquiries including pollution, contaminated land and chemical misplacement, refer the caller to EPA Pollution Watch Line: Metropolitan – 9695 2777 (24 hours) Regional – 1800 444 004 (24 hours).
