Select right nozzle for job
The last few years have brought many advances in nozzle design. The main improvement has been nozzles that reduce the formation of driftable droplets (under 200 microns) while still producing a droplet spectrum that provides the level of coverage required for consistent, postemergence weed control.
The primary factor determining the right spray nozzle is the product being used. Most herbicide labels specify either the nozzle type or droplet size (i.e., fine, medium, coarse) that should be used (see table). Unfortunately, no uniform system provides this information on labels.
A standardized system of classifying droplet size has been adopted, and this information is provided by nozzle manufacturers. Droplet size classification is determined by nozzle type, size and operating pressure. For example, an XR TeeJet 11004 operated at 40 pounds per square inch is rated at medium; whereas at 50 psi, it is rated at fine. When choosing nozzles, be sure to consider the full range of operating pressures they will be operated under when using rate controllers that adjust operating pressure based on sprayer speed.
The Enlist Duo label lists specific combinations of nozzles and pounds-per-square-inch ranges that may be used with this product. This is a new method of regulating the risk of drift associated with herbicide applications adopted by the Environmental Protection Agency. Only nozzles that have been evaluated for the range of droplet sizes produced when applying Enlist Duo can be recommended on the label. Additional nozzles are likely to be added to the label as new information is developed.
Spray volume also affects herbicide efficacy. Postemergence applications are often made when weeds are “shielded” from direct contact with the spray by the crop canopy. Spray volume can have more of an impact on the ability to achieve good coverage of targets within a canopy than the nozzle type. Most herbicide labels recommend increasing spray volume when making applications to large weeds or in situations with dense canopies.
As herbicide programs are adjusted to account for development of weed resistance to herbicides, the need to alter application methods is often overlooked. Sprayers must be properly equipped and calibrated to optimize herbicide performance and minimize off-target movement.
The use of trade names in this article is for clarity. Due to the large number of generic products, Iowa State University can’t include all products. Inclusion of a trade name does not imply endorsement.
Source: Iowa State University
* “NS” indicates the nozzle type or droplet size was not specified on the label.
This article published in the March, 2016 edition of WALLACES FARMER.
All rights reserved. Copyright Farm Progress Cos. 2016.