Getting the best out of each crop-protection product requires that the spray droplets are deposited in sufficient numbers at the right location, and at the right time in the pest, weed or disease life cycle.

Knowing where the droplets need to land requires knowledge of the target (e.g. plant structure and characteristics of the leaf surface), as well as an understanding of how the product translocates once the droplets have deposited onto the plant or leaf surface.

Knowing where the droplets should land is the starting point for any spray application; successfully achieving this can be difficult without being able to make an assessment of where the droplets are actually depositing.

There are several simple techniques and tools available to help the spray applicator to assess where sprays are depositing. These include:

• evaluating the level of control (efficacy) after each spray job – this can work particularly well when using fast-acting contact herbicides, such as paraquat;

• using coloured dyes, which can indicate where the spray has been applied;

• the use of fluorescent dyes and blacklight ultra violet torches or lamps, which makes it easier to see where small droplets (not visible using coloured dyes or that may not leave a stain on water-sensitive paper WSP) have landed; and

• using artificial collectors such as Water Sensitive Paper (WSP), which can be placed at various locations in the crop canopy, on the soil or within standing stubble where the droplets need to deposit.

Find out more

For more information on product uptake and translocation go to Module 2: Product requirements

The technique selected will depend on the amount of time and money the applicator is willing to invest in assessing spray coverage. The return on the initial investment for assessing spray coverage can far outweigh the expense of conducting the tests, particularly if this process provides the operator with information that will improve their sprayer’s set-up or how they operate the machine.