The right amount in the right place. That seems simple enough as a goal for pesticide application, and it sums up much of the effort in selecting and calibrating application equipment. It also sheds light on some reasons why pesticide drift is a problemit is one way to end up with the wrong amount in the wrong place. There are some recent nozzle designs available to applicators that can help control drift. |
Pesticide drift is talked about in two lights: vapor drift and particle drift. While both are important, there are some new nozzles available for reducing particle drift. The key to particle drift is that it increases as wind speed increases and is caused mainly by the smaller drops created when you spray. Managing droplet size is the focus of new nozzle designs. Many of the newer nozzles incorporate two designs for drop-size control. These are the pre-orifice and the turbulation chamber.
In a traditional nozzle the exit orifice, or hole, has mainly two functions. First, it meters the amount of fluid that can be sprayed out, based on its size. Second, it creates the spray pattern, based on its shape. Many drift-control nozzles divide these two functions between two separate orifices. The pre-orifice, or first hole, meters the flow of the fluid when it enters the nozzle. The liquid then leaves the nozzle through the exit orifice, where the spray pattern is formed. This reduces pressure on the liquid as it exits, resulting in larger drops.
A turbulation or mixing chamber is another feature of many drift-reduction nozzles. In this chamber of the nozzle, there is extra room for the liquid to expand and slow down before it is sprayed out. This puts less energy behind the liquid when it is sprayed out, creating larger drops and a more uniform pattern.
Two of the most talked-about types of nozzles today are air-atomizing nozzles and the turbo flat-fan nozzle.
Air-atomizing nozzles are available from numerous manufacturers by different trade names. These nozzles use a pre-orifice and then draw air into the mixture through a carburetor-like venturi. The air and liquid pass through a mixing chamber and are sprayed out together. The exit orifice is larger than on traditional nozzles because, in addition to the liquid of the spray, the incorporated air must also pass through. The larger exit orifice works with the pre-orifice and mixing chamber to produce larger droplets. Air bubbles are not present in the droplets when spraying only water but may be present when using certain chemicals or adjuvants. Manufacturers list operating pressures for these nozzles between 30 and 100 psi.
The turbo flat-fan nozzle also uses a pre-orifice and turbulation chamber but does not draw air into the spray mixture. The liquid is metered by the pre-orifice before it passes through a turbulation chamber, where the pressure on the spray is reduced. The spray then exits through a slot, forming a flat-fan pattern. These nozzles show very good pattern uniformity and drift reduction over a wide range of pressures. The manufacturer lists operating pressures for these nozzles between 15 and 90 psi.
Using Drift-Control Additives
There are many adjuvants available that are marketed for reducing spray drift. Research and field use have shown that these additives can greatly reduce spray drift when used with traditional nozzles. Those who want to use drift-reduction additives along with one of the new drift-reducing nozzles may be concerned about the effect on spray pattern. It is important to check the pesticide label and compare the recommended droplet size for the application to the droplet size the nozzle will produce. Droplets produced by drift-reducing nozzles may require less of an increase in size than droplets from traditional nozzles. This means that different nozzles may require different rates of a drift-control additive.
To determine how much drift control additive to use, begin with its label. Try the rates out with clean water before spraying, starting at the low-use rate. Observe the spray pattern to see if the nozzle will function properly within its operating pressures and that the spray patterns achieve the proper overlap. Work up to higher rates if necessary, but, if the pattern is too narrow or stringy, use a lower rate. Spending a little time determining a good rate can prevent an encounter with a few hundred gallons of unsprayable goo.
Take a Look
New nozzle designs available can give applicators good options in controlling drift. It is worth the time to flip through a nozzle catalog and see what is new in pesticide application today that can provide benefits in reducing drift.--Mark Mohr