Why is pesticide input efficiency so important?
Being more efficient with pesticide inputs has three main benefits for growers - it helps reduce farm costs (through a reduction in poorly targeted chemical and unnecessary spray applications) reduces environmental risks (by demonstrating the industry's adoption of pesticide management practices) and critically, limits the evolution of resistance in target insect pest and weed populations.
What do you need to know?
How to achieve pesticide input efficiency
Pesticide input efficiency means delivering the correct dose of the most appropriate pesticide to the target, while meeting all legal requirements and not adversely impacting people, property or the environment.
What you need to consider:
- Start with product selection: the aim is the best result with the least impact on non-target species, including beneficials.
- Accurately deliver the correct dose to the target: this includes correct rate, choice of band percentage, choice of application volume, mixing procedures, timing of the application (pest's life cycle) and spray quality (droplet size and spray coverage).
- Utilise the appropriate equipment and techniques: consider nozzle selection, operating pressure, nozzle height about the target, operating speeds, choice of adjuvants and managing water quality.
- Manage the spray operation according to meteorological and environmental parameters. Are the conditions right for spraying? Sometimes the best deicison is to delay until conditions are suitable.
- Make decisions about the use of each pesticide to minimise or prevent potential impacts to people, property or the local environment.
Spray drift: what it is?
Spray drift can occur as droplets and particles or as vapours.
Droplet and particle drift is a common cause of off-target damage from pesticides. Water in the spray droplets evaporates resulting in finer droplets and particles of herbicide. Smaller droplets remain airborne longer and are susceptible to further evaporation, often drifting kilometres away from the intended target. Under good spraying conditions, droplets tend to be carried downwards, towards the ground by air turbulence and gravity to collect on the intended plant surfaces.
Vapour drift is the movement of volatile components of herbicides in air currents during or after application. Volatility refers to the likelihood that the herbicide will turn into a gas. Vapours may arise directly from spray or from the target surface for several hours, or even days, after application. The risk of vapour drift can be avoided by choosing active ingredients with low volatility. The amine and salt forms of herbicides have a lower volatility than the low volatile ester forms, although even products with low volatility are still susceptible to droplet and particle drift.
How to manage spray drift
- Spray release height: The amount of spray chemical left in the air may increase by up to 8-10 times as nozzle height increases from 50cm to 1metre above the target. It is important to set the height of the boom at the minimum practical height to achieve the correct spray pattern for the nozzles. Vertical movement (boom bounce) of the spray boom should be minimised.
- Travel speed: Speeds above 15 km/h have been shown to increase the risk of drift by boom spraying, and speeds above 10 km/h increase the risk from shielded sprayers.
- Nozzle pressure: Nozzles should never be operated outside of the pressure range recommended by the manufacturer. Higher or lower than recommended pressures change the droplet spectrum and the spray pattern, affecting both the risk of drift and the efficacy of the spray application.
- Water volume and quality: Typically in-crop applications to cotton will require application volumes of 100 L/sprayed hectare or more. Meanwhile, for fallow spraying in low stubble situations with tranlslocated herbicides (such as glyphosate and the phenoxys) equivalent efficacy has been shown for medium, coarse and even extremely coarse spray qualities at 50 L/ha and above.
- Maintenance and hygiene: The output of each nozzle should be checked pre-season and regularly during the season. Nozzles that vary more than 10 percent from manufacturer’s specifications should be replaced. Application equipment that has been used to apply herbicides should be thoroughly decontaminated before being used to apply any product to a susceptible crop.
- Aerial applications: Higher airspeeds can cause air shear, where droplets shatter into smaller sizes. Some faster, larger turbine aircraft have difficulty in producing a coarse spray quality due to their fast airspeed. Reducing air speed (through slower aircraft) and/or reducing nozzle angle or deflection is an efficient way to reduce air shear.
SataCrop: locate cotton fields before spraying
Cotton Australia has partnered with Precision Crop Technologies (PCT) to deliver a new era of spray drift prevention, SataCrop. After a successful trial at Emerald QLD, the new mapping tool is now available for the 2019-2020 summer season. SataCrop is a digital platform that maps all crops, not just cotton, allowing growers and applicators of all products to be better informed before spraying.
The new technology requires growers to only map their fields once and has the ability to import field boundaries from compatible software such as PCT, SST, Farmworks, John Deere and Agworld. Interested in using SataCrop? Simply email Ben Boughton: firstname.lastname@example.org
What impact does the weather have?
Weather conditions are not only a primary determinant of efficacy, they determine whether the spraying operation should proceed, be delayed or aborted. Weather conditions need to be checked regularly during spray applications and recorded as per label requirements. Growers can subscribe to websites (such as Nufarm's spray wise decisions or Syngenta's weather website) that provide forecasts of conditions for spraying up to 10 days in advance.
The three main considerations are:
- Temperature and humidity: Higher ambient air temperatures and lower relative humidity conditions increase evaporation rates. Drift tends to increase when evaporation levels are higher.
- Surface temperature inversion: DO NOT SPRAY when a surface temperature inversion exists. During a surface temperature inversion, distinct, isolated layers of air form close to the ground, and the potential for spray drift is very high. The greater the difference between daily maximum and minimum temperatures, the stronger the surface temperature inversion is likely to be.
- Wind: It is best to apply pesticides when the wind is blowing away from sensitive areas and crops. Wind speed must be steady between 3 km/hr and 15 km/hr (during daylight hours, and above 11 km/h at night). Avoid calm, variable or gusty wind.
Calculating banded sprays
Banded sprays enable the recommended rate of the product to be placed on to an area smaller than the whole field (thereby reducing the total volume of chemical over the whole field, but still applying the equivalent rate/ha to the actual target area).
The Ispray Banded Spray Calculator for cotton determines suitable nozzle size, flow rate and rate controller settings for banded applications. The calculator can adjust speed and application volume to adjust the setup to determine optimum settings for an application.
So, what should you do on your farm?
- Keep comprehensive records.
- Establish communication processes to manage safety and reduce risks.
- Give careful consideration to the selection and application of pesticides.
- Use the correct application equipment and techniques.
- Ensure chemicals are transported, handled and stored appropriately.
- Dispose of unwanted chemicals and chemical containers appropriately.
- Always follow label instructions when handling and applying chemicals, including specifications regarding spray quality, spray conditions including mandatory wind speed range, and no-spray zones/buffers.
- Ensure all staff responsible for handling and applying pesticides are qualified according to relevant state and federal requirements.
- Maintain a manifest and Safety Data Sheets for chemicals deemed to be hazardous.
- Map your cotton fields on SataCrop.
Where should you go for more information?
- WEEDpak Herbicide Damage ID Guide
- Cotton Pest Management Guide
- Australian Cotton Production Manual
- Guide to keeping records of herbicide distribution (QLD Government)
- Pre-season spray checks fact sheet
- Keep the spray on the weeds fact sheet
- Back Pocket Guide Nozzle Selection fact sheet: nozzle selection for boom, band and shielded spraying
- GRDC spray application manual
- GRDC weather essentials for pesticide application fact sheet
- GRDC surface temperature inversions and spraying guide
- Cotton Australia summer weed control best practice guide
- Decontamination guide
- CottonInfo fact sheet:
- CottonInfo case study:
- SataCrop: a Cotton Australia and Precision Crop Technologies (PCT) initiative designed to highlight the location of cotton fields.
- Nufarm's spray wise decisions: provides forecasts of conditions for spraying up to 10 days in advance.
- Syngenta's weather website: provides forecasts of conditions for spraying up to 10 days in advance.
- Ispray Banded Spray Calculator: determines suitable nozzle size, flow rate and rate controller settings for banded applications.
- drumMUSTER: Recyling program for agricultural chemical containers.
- Spray clock diagram: 24 hour risk profile for summer spraying