WITH an accurate digital map that shows where weeds are right now, most boomsprayer rigs can become low-cost spot sprayers.
As farmers get their hands on fast and accurate weed mapping technology, the frequency of blanket herbicide spraying can be greatly reduced.
For the past two years John Single and his son Tony have been using the airborne weed sensor, Single Shot, developed by John's other son Ben, to rapidly detect and map weeds on their dryland cropping property in Narratigah, New South Wales.
Ben saw the benefits of separating the weed detection and weed spraying tasks and set about building the platform and working with Robotic Systems to bring the idea to reality.
John said the main aim was to stay ahead of herbicide resistance.
"Ten years ago we started work on developing drone-mounted sensors that could take over the task of detecting weeds in a green-on-brown situation," John said.
"Many sprayers, particularly later models, do not require any modifications and there are many benefits in having the weed mapping done separately rather than on-the-go."
Weed maps enable growers to take a planned approach to their weed management throughout the year and to build an historical record of weeds in a paddock.
The Single Shot sensor maps green-on-brown but are not limited to fallow situations.
The sensors can be used in newly-sown crops to map weeds that emerged on the planting rain or were missed in a previous application.
These patches, or individual weeds, can be treated in-crop or a pre-emergent can be applied to the patches at the end of the season.
The sensor can also be used in-crop to identify high biomass areas within a paddock where high weed density requires more drastic action, such as cutting for hay, and in wide-row crops where the canopy does not fully close and weeds can be detected between the rows.
The Singles have used the Single Shot technology in several different management scenarios already and the possibilities seem endless.
John said they have used the sensor to identify survivor marshmallow and milk thistle plants in fallow and then spot spray them with a high rate of Starane to prevent seed set.
"We have mapped feathertop Rhodes grass in wheat to generate a map for applying pre-emergent herbicide post-harvest and have filtered data to segregate weeds based on size," John said.
"That gives them the option to apply a blanket spray on smaller weeds and a herbicide spike to treat larger weeds, or to use a second boom to apply two different products or rates.
"Where pre-emergent herbicides are used, a perimeter determined by the user can be added to cover the seed distribution area of the mother plant."
Another important role for Single Shot at Narratigah is to scout for survivor weeds after herbicide applications.
The Singles crop 4500 hectares and can map the farm at a rate of up to 300ha per hour, targeting weeds greater than five centimetre diameter, this is one of the most important tasks in a herbicide program and yet it is generally not done effectively due to the time required.
Critically, data processing can be done in the field, if the internet is available at the site, and is done at a speed 1.7 times faster than flight time.
Once a weed map has been created, the drone can be sent out again to take high resolution imagery of plants in specific locations in the paddock for identification purposes, allowing John and Tony to plan a herbicide program with their agronomist, based on exactly what's in the paddock.
When it comes to spraying, having the weeds mapped before the spray operator gets in the cab means that the job can be done when conditions are suitable, including at night.
The real power of the Single Shot system is the ability to run simulations and to re-process the data to fine-tune a herbicide program based on weed size or density.
The sensor requires just a 1cm 'brown' perimeter around a weed to be able to detect the weed size.
The weed maps are built from images that are 10,000 times higher resolution than satellite images, giving a 1cm sampling size.
Every part of the paddock is photographed twice so obstacles such as stubble can be significantly reduced.
The drone flies at a height of 75 metres, following a predetermined path, and can also be flown lower and or slower if necessary to collect specific data.
"Information is power and this has really put us back in control of our weed management," John said.
"We know how much chemical to buy to do the job at hand, we know the costs and can alter the chemistry to suit a budget if necessary, we can choose to blanket spray or spot spray, and our ability to apply the double knock tactic is greatly improved."
In a bid to be one step ahead of the game, the Single Shot software will also calculate the shortest path for the sprayer, which is most useful when doing spot spraying on an ATV, or in the future, to deliver herbicide via a drone-mounted sprayer (UAV) or autonomous vehicles.
Ben said they ran a scenario for treating about 2000 survivor weeds in a 125ha paddock using a spray drone.
"To apply a blanket spray to the paddock, the spray drone would need to travel about 310 kilometres," Ben said.
"Using the Single Shot software we determined the shortest path to reach all the weeds, which cut down the time required to do the job to just two and a half hours.
"The sprayer would only be applying herbicide for 16km of the 54km flight, and just five per cent of the paddock would have herbicide applied."