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Match sprayer to new herbicides

Lynn Betts Betts Water Hemp after burndown
Glyphosate-resistant waterhemp survived a preplant burndown with glyphosate in this Iowa cornfield last spring. Resistance to glyphosate is leading many producers to use new combinations of both pre-emerge and post-emerge herbicides this year.
Study new herbicide labels and prep sprayer this winter to prepare for resistant weed battle.

THINK Different.

Don’t assume application requirements of new products and strategies to control resistant weeds will mimic those of glyphosate and other products you’re familiar with, cautions Dr. Mark Hanna, Iowa State University Extension Agricultural Engineer. Look now at labels of herbicides you’re considering for use next spring to prepare for proper nozzles and travel speeds, and keep from getting boxed in with mixes that don’t fit your equipment or that would put you off-label.


If you do your own spraying, and you’re considering new products this year to combat herbicide resistance, Mark Hanna says it’s a good idea to get to know your products now. “Most producers have shifted away from post-only applications to more reliance on a broader spectrum of both pre- and post-emerge herbicides,” the Iowa State University Extension Agricultural Engineer told a crowd at ISU’s Integrated Crop Management Conference recently, “and one set of sprayer nozzles probably won’t do it any more.”

Mark Hanna, Iowa State University Ag Engineer

Hanna says operators may need to reacquaint themselves with application requirements of various herbicides. “As nozzle size increases, you get larger droplet sizes, and as pressure increases, you get smaller droplet sizes,” Hanna says. “Many applicators are comfortable with a specific set of nozzles they use for glyphosate,” Hanna continues, “but with a broader set of pre- and post-emerge herbicides, we see more and more labels with specific nozzles and operating pressures. You can go off-label if you drive faster and increase pressure without changing sprayer tips. So it’s really important to prepare now and read the labels closely for the combinations of herbicides you’re thinking of using. If you change a product, it may mean a change in tips or a change in speed.”

Because sprayer travel speed will likely vary in the field from soil or weather conditions, take time this winter to check speed effects to determine maximum and minimum operating pressure and the resulting spray quality from the nozzle at these pressures. Coarse spray quality that’s acceptable according to the label at a lower travel speed can become unacceptable medium or fine spray quality as the controller increases boom pressure for faster travel speed when covering more acres per hour are desired, Hanna says.

 Dicamba nozzles

Hanna says the new dicamba GMO resistance technology will require Turbo Teejet Induction (TTI) nozzles with ultra or extremely coarse spray quality. The nozzles will reduce the fraction of small, drift-prone droplets to a minimum. That’s a big difference from the much smaller droplets commonly called for with glufosinate, on the other hand. In another example, specific nozzles and sizes from several manufacturers are listed as acceptable choices on the Enlist Duo label, but with specific maximum allowable operating pressures for each nozzle choice.

 Know pesticide labels

“Expect to see more specific label requirements on spray quality and approved nozzle types, including sizes and range of operating pressures, boom height, sprayer sanitation/cleanout, and acceptable tank additives,” Hanna says. “There may also be more specific restrictions on weather conditions, application rate, buffer requirements, and travel speed than were on earlier products.” 

Hanna says there are issues with high spray booms and drift, too. “What worked in the past may not work now,” Hanna says. “Maximum boom height above the target crop canopy may be specified. Keeping boom height roughly the distance of nozzle spacing along the boom or no greater than 24 inches above the target area helps eliminate drift potential while maintaining nozzle overlap.


 Sprayer cleanout

Hanna says to prepare to clean more than the tank. He recommends cleaning the strainers and boom sections, particularly the dead spots. He says label directions for cleaning equipment may include:

  • Drain the sprayer and don’t leave product in the sprayer overnight;
  • Use a preliminary flush with clean water and inspect filters (strainers, screens, etc.).
  • Follow with use of a commercial detergent, sprayer cleaner, or ammonia solution to triple rinse the system, allowing 15 minutes with agitation for each tank rinse with clean water.
  • Small dicamba concentrations have potential to produce visual plant symptoms, so consider rinsing off eternal parts of the sprayer chassis that may touch plants.

“Tank additives such as other herbicide products and adjuvants, including drift control adjuvants, shouldn’t be used unless specified on the label,” Hanna says. “Adjuvants do not have a uniform droplet size effect on all pesticide solutions and are being individually tested with newer GMO herbicide-resistant technology. Ammonium sulfate (AMS) or ammonium salts will not be allowed to be mixed with new dicamba technology because of its potential effect on spray solution to increase product vapor pressure.”

Hanna also warns against using old products with new herbicide resistant technology. “Substituting older versions of similar products will not only be off-label in many cases, but it also potentially creates other problems like crop injury, offsite drift potential, and pesticide residue affecting harvest or preplant intervals and worker protection,” Hanna says.


Winter checklist:

Use the winter offseason to consult labels for application requirements, looking especially for new product technology you may not be familiar with. New application requirements may differ from those of older familiar formulations. 

  • Determine what nozzle type and pressure will be required for each herbicide.
  • Check your existing nozzle inventory.
  • Clean strainers and boom sections, particularly dead spots.
  • Check the effect of slower or faster travel speed on operating pressure and resulting spray quality of the nozzle selected for each application, including drift.
  • Be prepared for more specific requirements. Recognize that newer versions of dicamba and 2,4-D formulations have more specific application requirements than older versions of similar products.



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