SPRAYING ADVISABILITY INDEX USING FIELD WEATHER OBSERVATIONS

A Spraying Advisability Index (SAI) for prediction of on-target spray deposition from a hydraulic boom sprayer is presented. It is intended for non-technical users such as farmers or custom sprayer operators. Advisability of spraying under the local weather conditions is determined from four measurements readily taken on site: wind speed, air temperature, relative humidity, and soil surface temperature. The index correctly predicted on-target spray recovery in 66 out of 82 trials conducted with water and a fluorescent tracer. When the SAI was favourable, recovery of spray from artificial targets was 80% or more of the quantity applied. Recovery was below this 80% cutoff when the SAI was unfavourable. Use of the SAI should reduce unnecessary environmental contamination due to spraying under inappropriate conditions, and will also improve application efficiency. It is particularly appropriate for post-emergence herbicide application or fungicide application.