Selecting nozzles for postemergence herbicides

Selecting nozzles for postemergence herbicides

When choosing spray nozzles, keep several things in mind to make the right choice.

An earlier ICM News article discussing effects of nozzle type and size on spray coverage prompted a question from a farmer regarding nozzle selection. The following answer and explanation is provided by Iowa State University Extension weed management specialist Bob Hartzler and ISU Extension ag engineer Mark Hanna.

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 (less than 200 micron) while still producing a droplet spectrum that provides the level of coverage required for consistent, postemergence weed control.

READ THE LABEL: The primary factor determining the appropriate spray nozzle to use is the herbicide product being used. Most herbicide labels specify either the nozzle type or droplet size classification (i.e. fine, medium, coarse) that should be used. Unfortunately, there is not a uniform system of providing this information on labels.

Related: Best Practices For Spraying: Get The Most Out Of Your Sprayer

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.

There is a standardized system of classifying droplet size
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.

Volume also affects how well herbicides control weeds
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.

Related: Palmer Amaranth: Understanding the Profit Siphon in your Field

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.

The use of trade names in this article is for clarity by the reader.  Due to the large number of generic products on the market ISU is not able to include all products.  Inclusion of a trade name does not imply endorsement of that particular brand of herbicide and exclusion does not imply non-approval.

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