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Drift Management: Nozzles or Drift Retardants   
by
Bob Hartzler

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April 20, 2007 Determining the effectiveness of drift control technologies is difficult since we can't see droplet movement and drift problems occur with such a small percentage of herbicide applications. Researchers at the University of Nebraska investigated the relative effectivenss of nozzle type and drift retardants, and concluded that drift-reduction nozzles are a more efficient method of managing drift than spray additives (Johnson et al. 2006). The experiment was repeated six times during 2000 and 2001 with wind speeds ranged from 3 to 20 MPH.

The effectiveness of the different tactics was evaluated by determining both droplet size and distance from the boom that herbicide injury symptoms were visible. As droplet size decreases, the number of droplets prone to off-target movement (drift) increases. The air induction nozzle produced the least number of small droplets, whereas the flat fan tips produced more small droplets than all other nozzle types (Table 1). The distance from the boom at which drift injury was visible was greater with flat fan tips than the other nozzle types. Reducing spray pressure (20 vs 40 PSI) using the flat fan did not significantly alter droplet size or distance of drift injury.

Table 1. Effect of nozzle type on formation of 'drifitable' droplets and
distance of visible drift injury.

Nozzle type

Droplet size (micron)1

Visible Injury (m)
Turbo TeeJet
250b
6.2a
Turbo FloodJet
261b
5.5a

Turbo Air Induction

284a
5.7a
XR flat fan (40 PSI)
240c
8.1b
XR flat fan (20 PSI)
222c
8.0b

1Droplet size indicates drop diameter that 10% of spray volume was below;
visible injury is distance from boom that herbicide injury was evident.

The air induction and flat fan nozzles were evaluated with several commercial drift retardants (Figure 2). A brief description of the spray additives is provided at the end of this article. None of the drift retardants caused a significant reduction in the distance that drift injury was observed when using flat fan nozzles. With an air induction tip, Border significantly reduced the distance of drift compared to the other spray additives and the control (no additive). When used with the AI tips, all of the additives reduced the number of small droplets compared to the control, but no additive reduced the number of small droplets when used with flat fan tips (data not shown).

Figure 2. Effect of drift retardants on distance of visible drift injury
with two nozzle types.

The authors concluded that 1) drift reducing nozzles were more effective at reducing off-target movement than drift retardants, 2) replacing nozzles would be a less expensive method of managing drift than drift retardants since nozzles would be a one time expense (for the growing season), and 3) use of flat fan nozzles should be discouraged during windy conditions due to the risk of off-target movement. The most important tool for managing drift is common sense by the sprayer operator - knowing when conditions are unfavorable for spraying. However, there will always be 'marginal' situations when wind speeds are higher than desired, but insufficient to shut down. It is under these conditions when the proper use of new technology can minimize off-target pesticide movement that creates problems for the applicator and farmer.

Drift retardant description:

Johnson, A.K., F.W. Roeth, A.R. Martin and R.N. Klein. 2006. Glyphosate spray drift management with drift-reducing nozzles and adjuvanats. Weed Technol. 20:893-897.

 

Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University

For more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-1923
Fax: (515) 294-9985
http://www.weeds.iastate.edu
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Common chemical and trade names are used in this publication. The use of trade names is for clarity by the reader. Inclusion of a trade name does not imply endorsement of that particular brand of herbicide and exclusion does not imply nonapproval.