App provides snappy spray assessment
GroundCover™ Supplement Issue: 122 | 02 May 2016 | Author: Bill Gordon
The SnapCard app is designed to help spray operators refine their sprayer set-ups for different jobs by measuring the spray coverage obtained
There are many variables that can impact on the outcome of a spray job and smart tools take some of the guesswork out of sprayer set-up to optimise spray coverage.
After product rate, the application volume and spray quality are the two main factors that drive sprayer set-up decisions and determine nozzle selection.
Water and oil-sensitive paper (WSP) is a resource that has been available to spray operators for many years to assess spray deposits (Figure 1). The WSP card has a special coating that produces a stain when a droplet lands on it.
Before the advent of image-analysis tools that could read WSP, spray operators relied on visual assessments of spray deposits and basic counts of droplets per square centimetre to compare spray set-ups. While this was useful for determining if spray was depositing where it was needed, this method does not provide useful numbers to determine which set-up provides better deposition.
Using droplets/cm2 to determine if spray coverage is adequate is only useful to compare similar droplet sizes (for example, a medium with a medium).
It becomes much more difficult to usefully compare 20 coarse droplets/cm2 to 20 medium droplets/cm2, as the amount of product deposited onto the target can be totally different.
In trials on spray coverage and pesticide efficacy during the late 1990s, it was difficult to find a consistent relationship between droplets/cm2 and efficacy, particularly when applying products with different spray qualities.
Laboratory-based image-analysis systems that were available at the time seemed to provide a more consistent relationship between the percentage of the target covered and the level of control obtained.
The SnapCard app takes WSP to a new level.
The SnapCard app has been available for Android and Apple devices since 2014, and its use by growers and spray operators to measure spray deposition continues to increase.
The app is the outcome of a research collaboration between the entomology group at the Department of Agriculture and Food, Western Australia, and the University of WA’s (UWA) applied entomology program, which was supported by funding from the Council of Grain Grower Organisations. The GRDC also provided funding to UWA for the employment of an entomology professor.
The SnapCard app can be used to predict and measure spray coverage on WSP. While the predictions, which are based on agronomic variables, weather conditions and sprayer set-up, serve as a useful guide with which to compare measurements. Perhaps the most powerful function of the SnapCard app is the measurement tool itself, which provides the user with a measurement of the percentage of the WSP covered.
In a recent University of Queensland study comparing some of the image-analysis systems available to measure spray deposits, results obtained from the SnapCard app supported results from laboratory-based equipment, which is often expensive and difficult to use in the field.
Results obtained from this study (Table 1) show the percent coverage on WSP as measured using a range of image-analysis systems. The nozzles and operating pressures used in this study were the American Society of Agricultural and Biological Engineers reference nozzles, which are used to determine the spray-quality classification for nozzles according to standard 572.1.
While the estimates of percentage coverage measured with SnapCard were marginally lower for 110-01 nozzle outputs than those measured by other instruments, there was good agreement with other instruments for the range of droplet sizes that are likely to be used by Australian grain growers.
Table 1 A selection of the data produced comparing the percent coverage measured by four of the image-analysis systems tested.
|Percent coverage on water-sensitive paper (WSP)*|
||SnapCard||Image J||Deposit Scan||Droplet Scan|
* As this is only a selection from the original data set the levels of statistical significance are not included.
SOURCE: University of Queensland Centre for Pesticide Application and Safety. Modified
from an article by Ferguson, JC et al (2016), Pest Management Science (in press)
To get the best out of The SnapCard app, spray operators should plan ahead and consider what comparisons they wish to make, and how to record and store the data.
Operators should collect a set of benchmarking data about how sprays are applied as a basis for comparison when making changes to parameters in the future.
Some growers have developed their own spray-application guides for their machines by photographing the WSP cards and recording the percent coverage for each set-up they use, as well as recording the impact of changing parameters such as pressure, application volume or travel speed.
Over time this record can become a valuable tool, especially when the information in the spray records allows for direct comparison between how the application was made and the results that were obtained.
Measuring spray coverage with SnapCard to identify areas of improvement
Many operators may not have considered the number of situations where an accurate measurement of the coverage could be useful for improving the sprayer set-up. While the following examples may not include every possible use of SnapCard, they do provide a useful guide for how to look at specific situations.
Assessing penetration into crop canopies
Placing WSP cards directly onto the crop canopy using staples or paperclips at various heights throughout the canopy can demonstrate how much penetration into the canopy can be achieved with different application set-ups.
The images in Figures 2 and 3 and Table 2 are from an example of using WSP cards and SnapCard provided by Bill Campbell of Farmanco Management Consultants in Western Australia. In this example, Mr Campbell worked with one of his clients to improve the spray coverage in canola for Sclerotinia sprays.
Figures 2 and 3 show the difference in coverage on WSP cards that a change in spraying speed with the same nozzles can produce, with the results summarised in Table 2.
Table 2 Summary of spray coverage at three positions in the canopy (top, mid and bottom) at two spraying speeds.
|Parameters to achieve 60L/ha||Top||Mid||Bottom|
|27km/h 2.3 ba||Coverage||11.2%||5.6%||3.5%|
|Droplets per cm2||80||45||36|
|22km/h 1.7 ba||Coverage||28%||18%||16%|
|Droplets per cm2||120||50||40|
SOURCE: Bill Campbell
Assessing spray deposits into standing stubble
To assess if the sprayer is set up to provide good spray deposition into standing stubble a comparison needs to be made between the spray deposits in the inter-row space and at the base of the standing stubble (within the stubble row). If a sprayer set-up can produce good spray coverage that is equivalent between the two locations, it generally indicates that the spray operator has selected an appropriate spray quality and application volume for stubble load and the spraying speed tested.
Determining wake effects and wheel-track issues
Placing WSP cards at different positions across the boom sprayer allows spray operators to look at the impact of changing travel speed on the amount of spray that deposits in the centre of the sprayer, adjacent to the wheels and out under the boom. This information is useful for looking at wheel-track issues and adjustments that can improve coverage.
Fine-tuning pulse-width modulation – highlighting coverage and duty cycle
Placing WSP cards at regular intervals, usually with a 2.5-centimetre gap between the cards, onto strips of timber that are at least one metre long can highlight possible coverage concerns if the duty cycle of a pulse-width modulation (PWM) system is too low to provide even coverage. Aligning the strips of timber with the direction of travel and spraying at different speeds will show the impact of low duty cycles, particularly with coarser spray qualities.
Identifying suitable travel speeds and sprayed widths with target-selectable sprayers
Placing cards on strips of timber aligned with the direction of travel, as described for PWM (see page 18), can quickly illustrate when the individual sprays turn on and off in relation to the position of a weed for target-selectable sprayers. Often it is useful to ensure the area for the trial is free of any green vegetation that might trigger the cameras, and to deliberately transplant weeds into the test area. Often when the spraying speed is not correct the spray droplets will deposit onto the WSP cards well before or well after the position of the weed.
The same timber strips, but this time aligned perpendicular to the direction of travel (parallel to the boom), with the centre of the strip aligned with the weed can show the sprayed width when the machine is operating at its usual spraying speed.
0429 976 565,
GRDC Project Code BGC00002, BGC00003
Was this page helpful?