Spray Coverage vs. Spray Drift
by Olivia Meyer, Iowa State University graduate student.
When apple growers plan their pesticide spray programs, they may think about a couple of important factors: spray coverage and spray drift. What’s the difference? How do we measure spray coverage? How do we manage spray drift?
In our research orchard at the Iowa State Horticulture Research Station, we are using an axial fan airblast (AFA) sprayer that was retrofitted with Intelligent Sprayer technology.
A standard AFA sprayer – they type of sprayer that has been around for nearly 70 years - uses fast-moving air from a fan to deliver sprays to the trees. In a way, the AFA airblast sprayer is “blind” because it doesn’t adjust the trajectory or amount of spray based on differences in tree size, shape, or amount of foliage.
On the other hand, an Intelligent Sprayer is different because it “sees” the trees as it sprays. It beams lasers at the trees, and a computer adjusts the amount and direction of spray in real time based on laser beams reflected from the trees.
What exactly is spray coverage? It’s the surface area of the apple trees that is covered by the pesticide. If spray coverage is poor, the gaps in coverage can be exposed to disease or insect pest attack.
Thorough coverage is always the goal. But how do you know if your coverage is adequate? This is one of the main reasons you calibrate the sprayer. A more precise way is to measure coverage by placing small cards (Water Sensitive Paper) at different points throughout the canopy. If the spray hits the card, it’s likely to provide good coverage in that part of the tree. In our project, we measure spray coverage at different point during the season so we can track coverage at a range of foliar densities.
What about spray drift? Spray drift is the spray that never hits it target. Spray drift can pose risks to applicator safety, environmental health, and neighborly relations. Spray drift also wastes money and can undermine the effectiveness of pest management.
What can you do to manage spray drift? In addition to proper sprayer calibration and operation, growers take note of weather conditions, especially wind. In doing research with the Intelligent Sprayer, we hope to see a big change in the way this new technology can target the trees by providing better coverage while reducing the volume of pesticides being applied. Achieving optimal coverage while minimizing spray volume can have a large impact on apple IPM practices. We can save costs and make the orchard a much safer environment!