Ensuring Adequate Spray Coverage: Take the Guesswork Out of Spraying

In agricultural spraying, accuracy is key. Yet with so many variables—such as spraying speed, droplet size, weather, and target density—getting the right coverage can feel like a guessing game. Knowing if your spray is landing where it needs to be is the first step toward optimising spray performance, and it starts with measuring your setup. By using practical tools like water-sensitive paper and UV fluorescent dye, spray applicators can benchmark their current practices, make targeted adjustments, and improve their overall spraying efficiency. 

Here’s a breakdown of the common factors that contribute to the overall accuracy and quality of your spray coverage.

Key Variables That Impact Spray Coverage

Several factors influence the quality of spray coverage in the field, including:

  • Target size and density: Is my target a waxy broadleaf weed, narrow ryegrass leaf or a sucking insect deep in the crop canopy? Larger or denser targets may require higher spray volume or smaller droplet sizes. 
  • Spraying speed and application volume: These greatly influence the amount of spray that reaches the target surface.
  • Droplet size and canopy density: Smaller droplets may penetrate dense canopies better but are more susceptible to drift. Larger droplets can also move through a canopy well but are more prone to bounce and runoff. 
  • Weather conditions: Wind, humidity, and temperature all affect droplet behaviour.
  • Wheel tracks and equipment setup: Adjusting equipment to minimise disruptions, such as wheel-track effects, can enhance coverage uniformity.

With these in mind, let’s explore some simple yet effective tools to help measure and improve your spray outcomes.

Water-Sensitive Paper: Capturing Coverage on Target

Water-sensitive paper (WSP) is a practical and widely-used tool that allows spray applicators to assess droplet deposits. 

WSP is coated to produce visible stains upon contact with liquid droplets, revealing the percentage of the paper covered by spray. 

To use WSP effectively, consider the following:

  • Placement: Position the WSP where spray droplets are expected to land. Placing it at various heights within the crop canopy, near stubble, or across wheel tracks can provide insights into how evenly spray is being distributed across different zones.
  • Assessment and Recording: Observe and record the percentage of WSP covered. This measurement enables comparisons between different spray qualities and configurations, such as droplet size and pressure.
  • Use with SnapCard: The SnapCard app, developed by the Department of Agriculture and Food in WA, offers a convenient way to measure WSP coverage. The app uses agronomic and weather data to predict coverage outcomes and allows applicators to directly compare actual results to expectations, guiding better setup adjustments.
  • Tabs + Clips Pack: These items assist with keeping the WSP dry from moisture on the ground along with keeping the WSP stable during windy conditions or down wash from a drone. The tabs and clips also stop the paper from rolling up once moisture has landed on the surface and begins to dry. If wanting to place the WSP on leaves to mimic this angle or check for underside of leaf coverage, simply use a stapler to attach the WSP to the intended target.

Purchase links:

Click here to purchase Water Sensitive Paper.

Click here to purchase WSP Tabs & Clips Pack.

Fluorescent Dye & Blacklight: Precision in Droplet Detection

When it comes to pinpointing where individual droplets have landed within a crop or on stubble, fluorescent dyes offer an advanced solution. These water-soluble, non-toxic dyes glow under a UV-A blacklight, making even tiny droplets visible in the field. 

Here’s how to incorporate this method into your spray analysis:

  • Application of Dye: Add the fluorescent dye to your spray mix. It will highlight droplet locations within the crop and on various surfaces such as leaves, stems, and soil.
  • Illumination with Blacklight: After spraying, use a UV-A blacklight or handheld UV torch to illuminate the spray zone. This makes droplets glow, helping to identify coverage across complex surfaces, such as crop canopies. This occurs at night so be sure to apply when no rain is forecast. 

Advantages of Fluorescent Dye: 

Fluorescent dye can provide valuable insights into spray penetration and the movement of droplets over leaves, which often can’t be captured with WSP. It’s also useful for assessing the thoroughness of decontamination or training on safe spray-mixing procedures.

Purchase Links:

Click here to Purchase 1L UV Fluorescent Dye

Click here to purchase 4L UV Fluorescent Dye

Click here to purchase UV Blacklight

Swath Gobbler: Comprehensive Deposition Analysis

For those needing deeper insights, the Swath Gobbler offers a full-spray swath analysis using portable onsite sampling and advanced data processing. The Swath Gobbler system includes:

  • Swath Data Collection: Utilises inexpensive calculator paper rolls and dye as a collector, providing a complete view of spray deposition across the swath.
  • Swath Gobbler Device: This portable unit reads and collects detailed spray data.
  • Post-Processing Software: Analyses swath data, highlighting variations across different parts of the spray zone for actionable insights.

The Swath Gobbler is particularly beneficial when using drone sprays, where variability in swath width can lead to uncertain application rates. By evaluating the actual deposition, operators can understand how changes in setup affect spray distribution and make informed adjustments for different conditions.

Purchase Links:

Click here to Purchase the Swath Gobbler Pro

Continual Improvement in Spray Practices

Spraying isn’t a one-size-fits-all task. With changing environmental conditions and target variability, maintaining consistent spray coverage requires regular measurement and adjustment. Tools like water sensitive paper, UV fluorescent dyes, and advanced systems like the Swath Gobbler offer tangible ways to assess and optimise your spray operations. 

By taking the guesswork out of spray applications, you’re setting yourself up for better outcomes, improved efficiency, and a more reliable approach to every spray job.

For more information about any of these tools, or to ask us a question about optimising your spray coverage efforts, get in touch with our team today.