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 with the proper selection and operation of application equipment.
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. It would seem that grapes and tomatoes wilt at the sight of a closed jug of growth regulator herbicides like 2,4-D or Banvel.
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 produce 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 more than 1,000 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 their version of so called low-drift nozzles. These nozzles reduce the number of small, drift-prone droplets, compared to 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 percent. 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.
Mike Rankin is the UW-Extension Crops and Soils agent for Fond du Lac County. Contact him at 929-3170 or email him at firstname.lastname@example.org.