Delta T is used by the agricultural industry. It is an important indicator for acceptable spraying conditions. It is indicative of evaporation rate and droplet lifetime. Delta T is calculated by subtracting the wet bulb temperature from the dry bulb temperature. When applying pesticides, Delta T should ideally be between 2 and 8, and not greater than 10. Select the right Delta T to determine the best weather conditions for spraying(PDF 593 Kb).
The diagram below relates air temperature and relative humidity to values of Delta T.