Since 1996, glyphosate has been the predominant herbicide used postemergence for weed control in corn, soybean and cotton in the United States. Because of that, glyphosate-resistant weeds have become increasingly more prevalent in glyphosate-resistant crops which have forced many growers to use other herbicides. Herbicide programs that relied primarily on glyphosate for weed control often used rates as low as 5 gallon/acre (GPA). The other herbicides being used in row crops often require a higher carrier volume according to the label when compared to glyphosate which can be burdensome to the applicator, requiring the transport of more water, more refills and more potential of mixing errors. Additionally, there is growing concern about off-target movement of pesticides and what can be done to mitigate pesticide drift. Both drift and efficacy can be affected by spray quality and application decisions such as nozzle selection, operating pressure and components of the spray solution

Creech, Cody

Fritz, Brad

Henry, Ryan

Hewitt, Andrew

Hoffmann, Clint

Kruger, Greg

English

Crossref

Pesticide application technology in the 21st century

Since 1996, glyphosate has been the predominant herbicide used postemergence for weed control in corn, soybean and cotton in the United States. Because of that, glyphosate-resistant weeds have become increasingly more prevalent in glyphosate-resistant crops which have forced many growers to use other herbicides. Herbicide programs that relied primarily on glyphosate for weed control often used rates as low as 5 gallon/acre (GPA). The other herbicides being used in row crops often require a higher carrier volume according to the label when compared to glyphosate which can be burdensome to the applicator, requiring the transport of more water, more refills and more potential of mixing errors. Additionally, there is growing concern about off-target movement of pesticides and what can be done to mitigate pesticide drift. Both drift and efficacy can be affected by spray quality and application decisions such as nozzle selection, operating pressure and components of the spray solution.</p

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  2013 Integrated Crop Management Conference - Iowa State University — 97Pesticide application technology in the 21st centuryGreg Kruger, Cropping system specialist, West Central Research and Extension Center/Agronomy and Horticulture, University of Nebraska-Lincoln. Brad Fritz, Agricultural engineer, USDA-ARS Aerial Application Technology Unit. Clint Hoffmann, Research leader and Agricultural engineer, USDA-ARS Aerial Application Technology Unit. Andrew Hewitt, Research professor, West Central Research and Extension Center/Department of Agronomy and Horticulture, University of Nebraska-Lincoln. Ryan Henry, Lab manager, West Central Research and Extension Center, University of Nebraska-Lincoln. Cody Creech, Graduate student, West Central Research and Extension Center, Agronomy and Horticulture, University of Nebraska-LincolnIntroductionSince 1996, glyphosate has been the predominant herbicide used postemergence for weed control in corn, soybean and cotton in the United States. Because of that, glyphosate-resistant weeds have become increasingly more prevalent in glyphosate-resistant crops which have forced many growers to use other herbicides. Herbicide programs that relied primarily on glyphosate for weed control often used rates as low as 5 gallon/acre (GPA). The other herbicides being used in row crops often require a higher carrier volume according to the label when compared to glyphosate which can be burdensome to the applicator, requiring the transport of more water, more refills and more potential of mixing errors. Additionally, there is growing concern about off-target movement of pesticides and what can be done to mitigate pesticide drift. Both drift and efficacy can be affected by spray quality and application decisions such as nozzle selection, operating pressure and components of the spray solution.Applicators should be aware that pesticide applications are complex and there are many applicator driven decisions which will impact both the efficacy and off-target movement of pesticides following the application (Figure 1). Every applicator should be aware of the potential effects starting with properly mixing and agitating the spray solution through the resulting droplet size and deposition from atomization of the spray contingent upon nozzle selection, operating pressure and spray solution composition. In general, every applicator should be aware of the weather conditions (especially wind speed), boom height, droplet size and distance away from susceptible vegetation.Pesticide drift is defined as the movement of spray particles and vapors off-target causing less effective control and possible injury to susceptible vegetation, wildlife, and people (National Coalition of Drift Minimization 1997). With the concern for reduced efficacy and environmental and legal ramifications of off-target movement, every applicator should strive to make as efficient and effective application as possible every time. Applicators should be cognizant that as wind speed doubles, research shows that in general we should expect the off-target movement at 90 ft. downwind to increase by as much as 700%. Also, it is important to recognize that wind speed and boom height are correlated. Wind speed is generally higher as you get further away from the intended target. Because the wind speed goes up as boom height increases and because the droplets take a longer period of time to reach the ground, research has shown that in general, we should expect to see approximately 350% increase in drift 90 ft. downwind when the boom height doubles. When applicators are making pesticide applications on days when wind conditions are nearly too high to make applications, they can manage drift more efficiently by getting the spray boom closer to the ground. Care must be taken so that the applications are not so close to the target that the pattern is lost however.As we move into an era where there is a reliance on postemergence herbicides other than just glyphosate, it is imperative that we revisit the practices which provide efficient and effective applications while minimizing off-target movement. While new formulations have been reported to have reduced off-target movement, the formulations only have so much influence. Irresponsible applications will move off-target regardless of how good formulations are or how good the adjuvants that are being used with the application are. 98 — 2013 Integrated Crop Management Conference - Iowa State UniversitySpray TankAtomizationImpactionRetentionDeposit FormationBiological EffectChemical ReactionsPump ShearEquipment/ApplicationMixing and AgitationPhysical PropertiesAtmospheric ConditionsEvaporationMicrometerological EffectsSpray and Surface PropertiesDroplet Size and Kinetic EnergyDynamic SpreadingSpreading and CoalescenceAbsorption and TranslocationSurface ActivityEncounter ProbabilityPick-up and Transport to the Site-of-ActionEquipment ContaminationDrift LossesInterception by Non-targetsRedistributionReflection, Shatter and SplashLossesLossesRedistributionRedistributionRun-offVolatilizationWeatheringLoss of ActiveLoss of DiluentVolatilizationEbert et al. 1999Figure 1. Pesticide applications include many complex relationships on the input and output of various steps in the process. The figure above depicts the steps involved in pesticide applications from the spray tank to the biological effect as described by Ebert et al. 1999.Droplet sizeDroplet size is often the easiest factor for applicators to manage in terms of off-target movement. Droplet size is influenced by the tank mix composition (pesticide(s) formulation, carrier product, and adjuvant(s) as well as the rate of each of those components), nozzle type and orifice size, and the operating pressure at the nozzle tip. Figure 2 illustrates how nozzle design and spray solution interactions affect droplet size for water compared to Roundup WeatherMax plus various adjuvants.   2013 Integrated Crop Management Conference - Iowa State University — 99114 41 2175 6 68123116 73 571 14 5 60 102550751000200400600XR 11005 TT 11005 TF 2.5 AI 11005 AIXR 11005PercentMicronsRWM + 2% AMSRWM + 2% AMS + micro-emulsion 1% less than 105 micronsWaterRWM + 1% AMS + polymerRWM + 2% AMS + micro-emulsion 2Figure 2. Influence of nozzle selection and adjuvant on the droplet size and % of the spray solution less than 105 microns. Interactions between spray solution and nozzle type can have a significant influence on droplet size distributions. Use of polymer adjuvants with Turbo TeeJet nozzles helped to manage the fines while the use of the same adjuvant with a Turbo Flood nozzle greatly increased the fines.Nozzle selection, pressure, and orifice size can change droplet size as much as 100-fold (Figure 3). Nozzles such as the flat fan have been used for decades for pesticide applications. These nozzles however produce many fines which have a much greater propensity to move off-target than larger droplets. By decreasing the pressure at which these nozzles are operated there will be an increase in droplet size. In the example in Figure 3, the % fines went from 26% to 15% when pressure on an XR110025 nozzle was decreased from 60 psi to 30 psi. The use of larger orifice nozzles and alternative nozzle designs can also lead to larger droplet size.100 — 2013 Integrated Crop Management Conference - Iowa State University0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.51.61.71.81.92.02.12.22.32.42.52.62.7Density distribution q3*4 0 6 0 8 0 1 0 0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0p a r t ic le  s iz e  /  µ mPKEY2012-12-18 08:26:08.3190 3230 H2012-12-18 08:28:03.7700 3230 H2012-12-18 08:29:17.1260 3230 H2012-12-18 08:31:50.9010 3230 H2012-12-18 08:33:09.1480 3230 H150 micronsFigure 3. Droplet size distribution curves for a XR110025 at 60 psi (red), XR110025 at 30 psi (blue), XR11005 at 30 psi (green), TT11005 at 30 psi (grey), and TTI1005 at 30 psi (teal). The graphic shows that reducing pressure and increasing orifice size will increase droplet size and decrease the % fines less than 150 microns. The graphic also demonstrates how nozzle selection and the use of air inclusion nozzles can be utilize to increase droplet size. Carrier rate In 2012, a series of studies were conducted to measure the influence of carrier volume on droplet size and weed control using four different postemergence herbicides commonly used for weed control in soybeans that use different herbicide modes-of-action. Field studies were set up at three locations across Nebraska. RoundUp PowerMax (glyphosate at 32 oz/ac), Liberty (glufosinate at 22 oz/ac), Cobra (lactofen at 12.5 oz/ac), and Weedone (2,4-D at 32 oz/ac) were applied at different carrier volumes. The four herbicides are an EPSP synthase inhibitor, glutamine synthase inhibitor, PPO inhibitor, and synthetic auxin, respectively. The four herbicides were each sprayed with appropriate adjuvants and were each applied at five carrier volumes (5, 7.5, 10, 15, 20 GPA). Droplet size of each treatment was evaluated at the wind tunnel facility in North Platte, NE, using a diffraction laser. Weed control ratings were recorded at three field sites located across Nebraska (Lexington, O’Neill, and Platte Center) at 14 and 28 days after treatment. The sprayed plots were 10 ft. wide and 30 ft. long. Planted across each plot were rows of non-herbicide resistant corn and soybean, velvetleaf, and grain amaranth. Treatments were replicated four times at each site.Generally, the performance of the systemic herbicides (glyphosate and 2,4-D) on weed control was not influenced by different carrier volumes. The abnormal behavior of the 10 GPA treatment of 2,4-D on soybean was likely because of the droplet size. That treatment was applied with an XR11001 nozzle using high pressure which would produce a high amount of fine droplets when compared to the other treatments. These small droplets are more prone to   2013 Integrated Crop Management Conference - Iowa State University — 101drift but provided better coverage. There was a lot of variability of glyphosate activity in general on the amaranth population which is not surprising as in the United States, amaranth has had considerable variability, a lot of genetic diversity and has been prone to evolve resistance. An interaction between the effect of carrier volume and the contact herbicides glufosinate and lactofen was clearly present. Herbicide efficacy in controlling velvetleaf increased from 52 and 37%, respectively, for these two contact herbicides, to 83 and 85% as carrier volume increased from 5 to 20 GPA (Figure 4). Control of the amaranth by glufosinate and lactofen increased from 56 and 81% to 80 and 100%, respectively (Figure 5). This is not too surprising since the Cobra and Liberty labels recommend 15 and 20 GPA, respectively. As applicators starting using products other than glyphosate for weed control, it will be important to understand the products that are being applied and what can be done to maximize the efficacy of those products.0	  25	  50	  75	  100	  2,4-­‐D	   COBRA	   LIBERTY	   ROUNDUP	  %	  Control	  Velvetleaf	  5	  GPA	  7.5	  GPA	  10	  GPA	  15	  GPA	  20	  GPA	  Figure 4. Visual ratings of 2,4-D, Cobra, Liberty and Roundup PowerMax injury on a velvetleaf at 5, 7.5, 10, 15, and 20 GPA.0	  25	  50	  75	  100	  2,4-­‐D	   COBRA	   LIBERTY	   ROUNDUP	  %	  Control	  Amaranth	  5	  GPA	  7.5	  GPA	  10	  GPA	  15	  GPA	  20	  GPA	  Figure 5. Visual ratings of 2,4-D, Cobra, Liberty and Roundup PowerMax injury on a grain type amaranth at 5, 7.5, 10, 15, and 20 GPA.102 — 2013 Integrated Crop Management Conference - Iowa State UniversitySpray qualityIn 2011, similar studies were conducted across Nebraska to investigate spray quality. Four locations (Elba, Courtland, Clay Center and Bancroft) had four replications. In each plot we planted non-traited corn, non-traited soybean, a crop type amaranth, velvetleaf, flax and quinoa.In the studies, we sprayed Roundup PowerMax at 11 oz/ac (glyphosate), Clarity at 4 oz/ac (dicamba), FirstRate at 0.15 oz/ac (cloransulam-methyl), Flexstar at 13 oz/ac (fomesafen), and Select MAX at 6 oz/ac (clethodim). All of these herbicides were used with the recommended adjuvants and all applications were made at 10 GPA. It is important to note that the rates used are approximately half of the recommended rate for each of these products. The use of these rates for weed control is never recommended, but for the purpose of observing differences in weed control these rates were necessary.Each herbicide treatment was sprayed through an XR1003 flat-fan nozzle at 43.5 psi, an XR11002 flat-fan nozzle at 40 psi, a TT11002 nozzle at 40 psi, an AIXR11002 nozzle at 40 psi and an AI11002 nozzle at 40 psi. The five nozzles when tested in water at these pressures should give Fine/Medium, Fine, Medium, Coarse and Very Coarse size spray qualities (droplet size ranges), respectively.For each of these nozzles and spray solutions, we determined the droplet size using a low-speed wind tunnel in College Station, TX. The droplet sizes were determined using a 7.5 mph wind speed across the nozzle and droplet sizes were measured using a SympaTec laser diffraction instrument. For the purpose of this article, the Dv0.1 or the size of the 10th percentile of droplets is reported. This value is useful as proxy for the potential for drift of each spray solution.As expected, certain herbicides preformed as well or better with large droplets while other herbicides performed poorly when droplet size was too large. Interactions between spray solution and nozzle type existed lending to the need for not only considering the ideal droplet size when making a spray application, but also using the most appropriate nozzle type. Further work in this area will be necessary to fully understand the interaction.For the Roundup PowerMax, a systemic herbicide, 16 oz/ac was effective at controlling all five species observed. Greater than 90% efficacy was observed using all five nozzles. This observation lends evidence to the potential shift in the tolerance of weed species that have been continuously exposed to glyphosate applications, even in fields where little or no glyphosate-resistance has been observed. However, because of the high level of efficacy, it was difficult to make comparisons between spray qualities.Since Roundup Ready systems have been widely adopted, the recommendation for glyphosate applications in these crops has generally been toward using nozzles and pressures which would give larger droplets. Our findings would support this recommendation as larger droplets would provide less potential for drift while delivering equal or better efficacy.The Dv0.1 values for glyphosate ranged from 70 to 230 for the nozzles using the glyphosate spray solution. As glyphosate concentration increases in the spray solution, it would be expected that the droplet size would change. When increasing Roundup PowerMax concentration in the spray solution from 22 oz/ac to 44 oz/ac, the droplet size would likely decrease.Clarity applications tended to have a similar trend as Roundup PowerMax in respect to the use of the different nozzles. There was little difference between the nozzles and therefore, the nozzles producing the largest droplets would provide a superior application, as the drift potential would be lower with these nozzles. This result is not of much surprise as dicamba (Clarity) is a systemic herbicide as well.FirstRate was similar to Clarity and Roundup PowerMax in that there really was not much difference in control between nozzles that produced different droplet sizes. The results from the FirstRate were somewhat dependent upon species. For example, the AI11002 nozzle provided the greatest control of the amaranth while the XR11003 flat-fan nozzle provided the greatest control of the velvetleaf.For both Flexstar and Select MAX, the larger droplets had reduced efficacy on the weed species for which we would expect control. An interesting observation was that the XR11002 flat-fan nozzle was not nearly as effective as the XR11003 or the TT11002 which both give slightly larger droplets, indicating that the droplet size can get too small for maximizing efficacy. This is a critical finding because these products are important as tank mixtures for postemergence applications to control glyphosate-resistant weed populations in soybeans.  2013 Integrated Crop Management Conference - Iowa State University — 103Impacts of application decisions on efficacy and driftDrift and efficacy are two critical components of any pesticide application. Without a high level of pesticide efficacy, there is no reason to make a pesticide application. Additionally, if there is a high amount of pesticide drift there is also no need to make a pesticide application. The problem is that for many different pesticides, the two components work in contrast to one another.For many of the pesticides that we use, although clearly not all, the smaller the droplet the greater the efficacy will be (at least to a limit). However, the smaller droplets are the ones most prone to drift. In cases where the pesticide is most effective with small droplets, there is a need for finding a balance between pesticide efficacy and drift potential.When making a pesticide application, wind speed and direction, distance to nearest susceptible species, and the toxicity of the pesticide should all be carefully evaluated and considered. Furthermore, intensive scouting and detail recording keeping should be done so that applicators are aware of how they made the application and the results that they obtained so that they can maximize their applications. While there are trends that can be followed such as reducing droplet size to minimize pesticide drift or following the label to make sure that adequate carrier rates, nozzles and pressures are used, much of what needs to be done to maximize the efforts of applicators needs to be made through tweaking the system based on scouting and observations.ConclusionsAs we move to more sophisticated cropping systems where multiple herbicide modes-of-action are utilized simultaneously, applicators should be aware of the ideal application conditions for managing off-target movement and pesticide efficacy for each product they are spraying. Particularly, as 2,4-D- and dicamba-resistant crops are developed, basic principles of pesticide applications should not be forgotten. While tools such as the Enlist Duo, Engenia and Roundup Xtend will provide growers with newer and safer options, they like all pesticide applications, have the propensity to move off-target and should be stewarded in a safe and responsible manner.Following label recommendations, spraying in appropriate wind speeds, keeping the boom at the correct height above the target, minimizing small droplets, and being cautious of environmentally sensitive areas near the application site are always recommended.ReferencesEbert, T.A. et al. 1999. Deposition structure and efficacy of pesticide application. 1: Interactions between deposit size, toxicant concentration and deposit number. Pestic. Sci. 55:783-792. 

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Pesticide application technology in the 21st century

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