By Bob Hartzler Professor of Agronomy
An earlier ICM News article discussing affects of nozzle type and size on spray coverage prompted a question from a farmer regarding nozzle selection. In recent years there have been many advances in nozzle design. The primary improvement has been development of nozzles that minimize the formation of driftable droplets (< 200 micron) while still producing a droplet spectrum that provides the level of coverage required for consistent, postemergence weed control.
The primary factor determining the appropriate spray nozzle is the product being used. Most herbicide labels specify either the nozzle type or droplet size classification (i.e. fine, medium, coarse) that should be used (Table 1). Unfortunately, there is not a uniform system of providing 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 not only by the nozzle type, but also by nozzle size and operating pressure. For example, an XR TeeJet 11004 operated at 40 PSI 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.
Table 1. Label recommendations for nozzle type, droplet size, and carrier volume (GPA).
| Product | Herb. Group | Nozzle type1 | Droplet size1 | GPA |
| Liberty (glufosinate) | 10 | Flat fan | NS | >10 |
| Cobra(lactofen) | 14 | Flat fan, hollow cone | NS | 10-20 |
| Reflex (fomesafen) | 14 | Flat fan, hollow cone | NS | 10-20 |
| Ultra Blazer (acifluorfen) | 14 | Flat fan, hollow cone | Medium | 10-20 |
| Armezon (topramezone) | 27 | NS | NS | >10 |
| Callisto (mesotrione) | 27 | Flat fan | Medium to Coarse | 10-20 |
| Laudis (tembotrione) | 27 | NS | Medium to Coarse | 10-20 |
| Roundup PowerMax (glyphosate) | 9 | NS | Use nozzles that avoid
generating a fine mist | 3-40 |
| Enlist Duo (2,4-D + glyphosate) | 4 | See label | NS | 10-15 |
| 2,4-D LVE | 4 | NS | Avoid nozzles that produce
small droplets that may drift | >3 |
| Clarity (dicamba) | 4 | NS | Coarse | 3-50 |
1NS indicates nozzle type or droplet size was not specified on label.
The Enlist Duo label lists specific combinations of nozzles and PSI 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 EPA. 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 herbicide resistance, the need to alter application methods is often overlooked. Sprayers must be properly equipped and calibrated in order to optimize herbicide performance and minimize the potential for off-target movement.