With the planting season also comes the spraying season and it’s probably a good time to be reminded that the off target movement of pesticides is both illegal and costly from the standpoint of reduced product performance and a potential fine or lawsuit.  

     Drift is the movement of a pesticide through air, during or after application, to a site other than that intended for the application.  Eliminating drift completely is impossible. However, it can be reduced to a minimum if chemicals are applied with some common sense and proper selection and operation of application equipment. 

What causes pesticide drift? 

     The major factors that influence drift are: spray characteristics, equipment/application techniques, weather conditions, and operator skill and care.  Spraying under excessive wind conditions is the most common reason why severe drift problems occur.  Quite simply, the best thing to do is not to spray under these conditions.  Sometimes a moderate wind speed is enough to cause problems if areas adjacent to a field are both susceptible to the product being sprayed and downwind from the target. 

     After wind speed, spray droplet size is the next most important factor affecting drift.  Research has shown that there is a rapid decrease in the drift potential of droplets with diameters greater than approximately 200 microns (about twice the thickness of human hair).

     The best situation is to spray droplets that are all the same size, and larger than 200 microns.  Unfortunately with most nozzles used today, this is not on option.  They produce droplets varying from just a few microns to over 1000 microns. The goal is to choose and operate nozzles that produce relatively fewer of the drift-prone droplets.  Fortunately, almost all major agricultural nozzle manufacturers have recently introduced their version of so called low-drift nozzles.  These nozzles are designed mostly for reducing the number of small, drift-prone droplets, than comparable size standard flat-fan tips at the same flow rate and operating pressure.  Research shows that these low-drift nozzles are capable of reducing drift potential by up to 80%.  If operators of sprayers pay attention to wind direction and velocity, and have knowledge of droplet sizes produced by different nozzles, drift can be minimized.

Finally, proper boom height and nozzle spacing for the type of nozzle being used will help reduce drift potential.