Spray volume key factor
Proper herbicide application is very important to ensure that products achieve their full potential for weed control. “For post-emergence herbicides, this includes application to appropriately sized weeds and equipping the sprayer to achieve uniform coverage of target weeds,” says Bob Hartzler, an Iowa State University Extension weed management specialist.
Hartzler, along with ISU Extension ag engineer Mark Hanna, discussed this topic with farmers and custom applicators at ISU Extension crop meetings this winter.
Weed scientists at Purdue University recently reported on the influence of nozzle type and spray volume on target coverage within the soybean canopy, says Hartzler. A traditional flat fan (XR) nozzle and three drift reduction nozzles were included in the study. The XR nozzle produced more driftable droplets than the other nozzles, and the two types of air induction nozzles had much less volume in small droplets than the XR and turbo twin jet (TTJ) nozzles.
Coverage of targets within the canopy was evaluated by placing water-sensitive paper at different heights within 12-inch-tall soybeans planted in a 15-inch row width. Averaged over nozzle types and spray volume, the coverage declined by about 50% from the top of the canopy to targets placed 4 inches above the soil surface.
The Turbo Tee (TTI) nozzle was less consistent than the other nozzles on coverage at the top and middle of the canopy. The TTI nozzle produces the largest droplet size of the nozzles evaluated, and thus would be expected to provide less uniform coverage than the others. However, nozzle type did not have a significant effect on coverage of targets at the bottom of the canopy.
The researchers speculate that large droplets were more efficient at penetrating the canopy than small droplets, therefore resulting in similar coverage by the different nozzles of targets placed at the base of the canopy.
Larger nozzle, better coverage
Regardless of nozzle type or target placement, better coverage was achieved with the larger nozzle that provided greater gallons-per-acre (GPA) spray volume. Averaged over nozzle types and the two years of the study, 15 GPA provided 26% coverage compared to 13% at 10 GPA.
“Thorough coverage of weeds is required to achieve consistent weed control, especially when relying on herbicides other than glyphosate,” says Hartzler. The concern over off-target movement of pesticides has led to the movement toward the use of nozzle types that produce fewer small droplets. This research demonstrates that spray volume has a greater effect on spray coverage than the type of nozzle. “Using spray volumes at the high end of the recommended range should improve the consistency of weed control,” Hartzler adds. “Nozzle selection should be based on herbicide label specifications.”
Source: Iowa State University
This article published in the March, 2016 edition of WALLACES FARMER.
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