Weeds are a significant yield robber in soybean. Our work has helped to better understand how to make pesticide applications in soybean while mitigating off-target movement. A good example of the findings from this work are that we now know that systemic herbicides appear to be responsive to droplet size and contact.
The objective of this study was to measure the impact of droplet size, herbicide concentration, and application speed on weed control for five commonly used soybean postemergence herbicides.
When averaged over all other variables, nozzle type had the greatest impact on droplet size. Droplet size rankings for nozzles, ranked smallest to largest using the Dv0.5 values, were the XR, TT, AIXR, AI, and TTI nozzle with 176% change in Dv0.5 values from the XR to the TTI nozzle. The impact on droplet size of the variables examined in this study in order of greatest impact to least were nozzle, operating pressure, herbicide, nozzle orifice size, and carrier volume.
Roundup PowerMax, Liberty, Cobra, and 2,4-D amine were applied in different carrier volumes. These four herbicides are an EPSP synthase inhibitor, glutamine synthase inhibitor, PPO inhibitor, and a synthetic auxin, respectively. Each herbicide was applied with the appropriate adjuvants and was sprayed across planted rows of non-herbicide resistant corn, non-herbicide resistant soybean, velvetleaf, quinoa, grain amaranth, and flax. At each location, increasing the carrier volume (5, 7.5, 10, 15, 20 GPA) of Roundup PowerMax and 2,4-D did generally not impact weed control. The one exception occurred when using 2,4-D to control soybeans and the increase in control was more related to droplet size than carrier volume. This is another example that demonstrates that in some instances, droplets that are too large may reduce weed control. Cobra and Liberty both performed the best at the highest carrier volume (20 GPA). Findings from 2012 demonstrated how carrier volume impacts droplet size and can also influence weed control.
The treatments consisted of four herbicides: Touchdown HiTech (a glyphosate formulation with no surfactant) at 32 oz/acre, Fusilade at 6 oz/acre, Cobra at 12.5 oz/acre and Clarity at 8 oz/acre. Each herbicide was applied alone and in combination with a non-ionic surfactant (NIS), crop oil concentrate (COC), methylated seed oil (MSO), high surfactant oil concentrate (HSOC), ammonium sulfate (AMS), and a drift reduction technology adjuvant (DRT). The adjuvants were applied at the following rates: NIS (0.25% v/v), COC (1% v/v), MSO (1% v/v), HSOC (1% v/v), AMS (17 lbs/100 gal), and DRT (4 fl oz/a). All adjuvants except NIS increased the droplet size and reduced the potential for drift with the herbicides evaluated. Generally, the addition of adjuvants increased the efficacy of the four herbicides tested when compared to the herbicide alone. The adjuvants performed differently with each herbicide and were often species specific and occasionally location specific (although results are combined across location for the purpose of reporting here). The addition of adjuvants is imperative to get the most out of every herbicide application, but further testing is needed to understand which situations are best suited for different application conditions and intended targets.
The objective of this study was to evaluate the effect of droplet size on the efficacy of six commonly used herbicides applied to different plant species that are either considered weeds or represent different in plant architecture and/or morphology. Generally, most differences observed were subtle and in many cases no clear pattern was readily discernable. Common lambsquarters saw an increase in control using small droplets when applying Clarity. The smallest droplet size when applying Liberty to control velvetleaf was the least effective. Applicators should consider the target species and environmental conditions when selecting a nozzle. Such an approach will limit the potential for off-target movement while delivering a lethal dose to the target plant.
Treatments included glyphosate with and without a drift control adjuvant applied at 10 and 20 GPA. The sprayer boom was divided into 5 sections and AIXR, AITTJ, TTI, and XR nozzles were each affixed in one of the sections. The fifth section was plugged and treated as the control. Initial analysis of the data reveals that canopy penetration increased proportionally as the GPA increased from 10 to 20 GPA. Using large droplets produced by the TTI nozzle increased penetration in the corn crop and small droplets of the XR nozzle increased penetration in the soybean crop which had a much denser canopy. When selecting a nozzle for an application considerations should be given to the crop canopy.
Treatments consisted of Clarity being sprayed through XR, AIXR, and TTI nozzles at 20, 37.5, and 55 PSI. These combinations were combined with MSO, NIS, Silicone, COC, DRA, and no adjuvant. A greater proportion of the spray was retained on the leaf surface when using the XR nozzle. The TTI had the least amount retained on the leaf surface. Increasing the pressure generally decreased the amount the remained on the leaf surface. Adjuvants, ranked in order of retention on the leaf surface, were MSO, NIS, Silicone, COC, DRA, and clarity alone. Using smaller droplets and lower pressures reduce the droplet velocity reducing the amount of droplets that rebound off the leaf surface, shatter, or roll off the leaf. The adjuvants affect the surface tension of the droplets reducing the incidence of droplet loss from the leaf surface. Drift is a huge concern with growth regulators and using large droplets can reduce the off-target movement during application. However, the use of such droplets can reduce the amount of herbicide that remains on the leaf surface to be taken up by the plant. Using adjuvants, and lower pressures can increase the amount available to the plant.