Weather and inversion transcript
The APVMA Operating Principles in Relation to Spray Drift Risk has meant that product labels have begun to contain additional information about the weather conditions to be observed when spraying the product. Before you start spraying, check that the weather is suitable for spraying. Some chemicals shouldn't be applied if it's expected to rain.
This is because some chemicals can wash off and become less effective, or also because some chemicals can wash away and damage sensitive vegetation or areas. Weather forecasting is useful for sprayer planning, but weather recordings must be taken in the paddock and the field of spray.
Unless your product label states otherwise, guidelines for better conditions are a delta T of between two and eight, temperatures below 28 degrees, no inversion layer present, a steady wind of 3 to 15 kilometres per hour, blowing away from sensitive areas. With an atmospheric inversion, the temperature of the air increases with altitude up to a point, and then it decreases.
While this might not seem like much of a change, it can have significant impacts on sprays, and has potential to trap and move them many kilometres from the point where they were applied. The inversion layer rises over the course of a day as the ground heats up and pushes the inversion higher.
Any crisp, still, early morning or evening should be a warning for a potential inversion, and spraying at night is even more risky. There are some signs that an inversion may be present, such as smoke or dust rising vertically then moving horizontally away from the target area. The inversion will be at the point the vertical smoke starts moving horizontally.
View the Weather and inversion video.