SPRAYING CONDITIONS GRAPH

The graph above indicates optimal and high risk times for pesticide application.

• The top half of the graph show the recent Delta-T,  with the green region being the optimal range of 2 - 8 degrees.
  
  
• The bottom half of the graph shows windspeed, with the green region being the safe range of <15km/h

THE PROBLEM

When applying pesticides, the aim is to maximise the amount reaching the target and to minimise the amount reaching off-target areas.

This results in maximum pesticide effectiveness and reduced damage and/or contamination of off-target crops and areas.

A pesticide which moves in the air from the target area to an off-target area is known as 'spray drift'

Application factors that can affect the risk of spray drift include droplet size, boom height, active ingredient volatility and ground cover.

WEATHER FACTORS AFFECTING THE RISK OF SPRAY DRIFT

Weather conditions during and shortly after application that are important to consider are:

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DELTA-T

Delta-T is defined as the difference between the wet bulb temperature and the dry bulb temperature.  It is directly related to the relative humidity.

• Delta-T <2 - too low for spraying - droplet life increased, high risk of drift.
• Delta-T >8 - too high for spraying - droplet life too short.  Spray will dry before it is fully effective

WIND SPEED

• .Ideal safe wind speed is 7--10 km/h.
• 11--14 km/h is suitable for spraying if using low drift nozzles or higher volume application
• Avoid spraying under still conditions.

INVERSIONS

The most hazardous condition for herbicide spray drift is an atmospheric inversion, especially when combined with high humidity.

Do not spray under inversion conditions