Delta-T and Spraying

When applying farm chemicals it is vital that they are applied under safe conditions. To help determine this, a Delta T value can be calculated. Delta T is an indicator of evaporative potential of spray droplets and is calculated from air temperature and relative humidity data.

If the air is very moist (i.e. very high humidity and hence very low Delta T) then the spray droplets will be short-lived and not effective. Conversely, when humidity is very low (and the Delta T very high) spray droplets will vaporise faster, travel longer distances and potentially cause off-site damage.

The ideal window for spraying is when the Delta T is between 2 and 8 °C. On the graph this corresponds to the green shaded area between the ‘lower limit’ (2°C) and ‘upper limit’ (8°C).


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