Grains Research and Development

Date: 28.05.2015

Weather essentials for pesticide application

Cover page of Weather Essentials for Pesticide Application booklet by Graeme Tepper for GRDC.

Typically, there is a short window of opportunity to safely and efficiently control pests and diseases in agricultural crops. The opportunity may be shortened by unsuitable weather conditions. It is therefore essential that spray applicators are able to identify and react to weather conditions at a local scale.

Weather Essentials for Pesticide Application aims to help those applying pesticides to understand, observe and interpret local weather elements. This knowledge will help them plan and effectively execute spray applications to avoid spray drift.

The weather factors that are important to the application of pesticides can be significantly and critically different to conditions indicated by weather forecasts, weather maps and off-site weather observations – especially overnight and into mid-morning.

The weather factors that need to be considered before and while applying pesticides are:

  • atmospheric stability (including up and down air currents); 
  • wind speed, direction and turbulence; 
  • temperature; and 
  • humidity.

Research has found that spray particles are likely to drift further and in higher concentrations when the atmosphere is stable and where there is a surface temperature inversion.

Field tests indicate that the greatest drift deposits occurred with relatively high wind speeds, coupled with a temperature inversion and spray in the small droplet spectra (about 200μm) (Bird 1995).

It is essential that all spray-rig operators understand how to recognise, and respond to, these weather factors to minimise the risk of spray drift and maximise the potential for the pesticide to reach the appropriate target.

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Graeme Tepper


Emma Leonard, AgriKnowHow

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GRDC & MicroMeteorological Research and Educational Services (MRES)

First published February 2012, revised January 2014.

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