Experiments were conducted to evaluate the impact of spray volume, nozzle type, adjuvants, the presence of dew, and their interactions on foliar retention of creeping bentgrass. Tartrazine, a common food dye, was used as a tracer in this study. Increasing spray volume from 95 L ha−1 to 1,500 L ha−1 decreased foliar retention efficiency from 98% to approximately 85%. Compared with flat-fan nozzles, air-induction nozzles delivered similar retention efficiency at all spray volumes evaluated. However, flat-fan nozzles provided higher uniformity and more thorough coverage. Adding nonionic surfactants, organosilicone adjuvants, or methylated seed oils at typical concentrations yielded retention efficiency of approximately 90% to 93% regardless of spray volumes. In contrast, with water alone, increasing spray volume reduced retention efficiency from 95.9% to 87.3%. Simulated dew applied at 1,950 L ha−1 increased retention efficiency by approximately 3% when spray application volume was 190 L ha−1, while no difference was observed at 750 L ha−1. The presence of dew reduced the impact of adjuvants on retention efficiency. Large quantities of dew, 3,800 L ha−1, did reduce retention efficiency.

Strawberries, an important Florida crop, are grown on raised beds covered with plastic mulch. The plastic mulch provides good control of many weeds, but some problem species can emerge from the transplant hole during crop establishment. POST herbicide options for broadleaf weed control within the strawberry bed is limited to clopyralid, which only provides suppression. Strawberry canopy shielding may be responsible for the observed incomplete control with clopyralid application for problematic broadleaf weed species such as black medic and Carolina geranium. Two field experiments were established on mature strawberries to evaluate spray penetration through the canopy. The first examined spray penetration through the canopy of multiple strawberry cultivars at various distances from the crown. The second examined the effects of application volumes and nozzle selection on spray penetration. Cultivar selection had no effect on spray penetration through the canopy. In the first study, when applying at 281 L ha−1, the area around the planting hole (0 to 5 cm from the crown) had 8% coverage below the canopy while the area below the canopy edge (10 to 15 cm from the crown) had 27% coverage. In the second study, increasing the application volume from 187 to 375 L ha−1 increased coverage by 81%. Increasing the application volume from 375 to 740 L ha−1 increased coverage 33% with maximal coverage of 53% at 740 L ha−1. Nozzle type (standard even flat spray tip, Drift Guard, or TwinJet nozzles) did not affect coverage or deposition volume below the canopy. Overall, mature strawberry canopies demonstrated similar spray droplet penetration across cultivars with increased penetration with increased distance from the crown. Penetration increased with increasing application volume, but the nozzle types used in this experiment did not affect penetration. Additional research is needed to better define the effect of application volume on herbicide efficacy.

Experiments were conducted to compare control of entireleaf morningglory with POST applications of DPX-PE350 applied with no adjuvant, a nonionic surfactant, or crop oil concentrate in spray volumes of 94, 235, and 375 L ha−1. Control was greater with a nonionic surfactant or crop oil concentrate than with no adjuvant and control with crop oil concentrate exceeded control with the nonionic surfactant. Spray volume had no effect on efficacy. DPX-PE350 was more effective when applied to foliage only or to soil plus foliage than when applied to soil only after emergence of entireleaf morningglory. Control from soil-only applications was lower on a silty clay soil than on a silt loam soil. Except for sicklepod, mixing DPX-PE350 with fluometuron or MSMA had little effect on weed control.

Control of seedling and rhizome johnsongrass [Sorghum halepense (L.) Pers. # SORHA] with five herbicides was evaluated after postemergence application in various diluents and spray volumes using one to three types of applicators from 1983 to 1985. The rate of each herbicide required to control seedling johnsongrass using paraffinic oil as the diluent in applications with an external- or internal-mixing air-assist sprayer at a spray volume of 9.4 L/ha was one-half the rate required when water plus 1.25% (v/v) paraffinic oil concentrate (POC) or water plus 1.25% (v/v) soybean oil concentrate (SOC) were the diluents in applications with a conventional sprayer equipped with fan jet spray nozzles at a spray volume of 187 L/ha. Rates were also reduced when once-refined soybean oil was the diluent at a spray volume of 9.4 L/ha, except for the ethyl ester of quizalofop {(±)-2-[4-[(6-chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid}. Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} was equally effective on seedling johnsongrass growing in soybeans [Glycine max (L.) Merr. ‘DPL 105’] when applied at 224 g ai/ha with an internal-mixing air-assist sprayer or a controlled-droplet applicator (CDA) at a spray volume of 9.4 L/ha and a conventional sprayer at a spray volume of 187 L/ha, regardless of diluent. Conventional application required the use of 1.25% (v/v) SOC or POC as part of the diluent to be effective. For three of the five herbicides evaluated on rhizome johnsongrass, paraffinic oil at a spray volume of 9.4 L/ha was the only diluent that resulted in season-long control. Rhizome johnsongrass control with this diluent also resulted in significantly higher soybean yields than all other diluent-spray volume treatments.

Atomizer type, spray volume, and herbicide rate influenced the effectiveness of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) in controlling vegetation. In general, paraquat controlled vegetation more completely when applied from atomizers that discharged sprays with the angle between the edges of the pattern less than 80°. Increasing spray volume increased control for marginal herbicide rates. Increasing herbicide rate increased control and tended to overcome less effective atomizer performance or reduced spray volume. Vegetation was effectively controlled with cone- or fan-pattern-type nozzles at spray volumes as low as 50 L/ha. Cone- and fan-pattern atomizers were equal to or more effective than either rotary or flooding-type atomizers in all tests.

Paraffinic oil applied at 2.3, 4.7, and 9.3 L/ha to the surface of johnsongrass [Sorghum halepense (L.) Pers. # SORHA] leaves spread to provide complete coverage of the leaf surface. Soybean oil applied at the same volumes provided only 30 to 50% coverage of leaf surfaces. Water at 187 L/ha that contained 1.25% paraffinic oil adjuvant provided only about 30% coverage because spray droplets did not spread appreciably. Spread coefficients obtained when five different oil-soluble herbicides were applied to leaf surfaces in paraffinic oil were more than 100 times greater than when applied in water alone. Higher spread coefficients were obtained when paraffinic oil contained herbicides than when paraffinic oil was applied alone. Spread coefficients were also much greater for paraffinic oil alone than for soybean oil with or without herbicides. Stomata on johnsongrass leaves were distorted by paraffinic oil, suggesting that leaf surface wax was dissolved and this might be a mode of entry of herbicide into johnsongrass when applied in paraffinic oil. Stomata were unaffected by soybean oil or by water sprays that contained 1.25% soybean oil adjuvant or paraffinic oil adjuvant.

Experiments were conducted in Massachusetts and New York to evaluate the potential influence of plant growth stage, spray volume, nozzle type, additional surfactant, and herbicide formulation on smooth and large crabgrass control in turf with fenoxaprop. At a well-watered site, crabgrass control with fenoxaprop was equal to or greater than with MSMA. On an irrigated, fertilized site, crabgrass growth stage did not influence fenoxaprop efficacy. Excellent control of up to 5-tiller smooth crabgrass was obtained with 0.20 kg/ha of fenoxaprop. On nonirrigated turf, fenoxaprop was less effective on tillered crabgrass than on 2- to 5-leaf weeds. Under very dry conditions, fenoxaprop was ineffective regardless of growth stage. Control with MSMA was less affected by drought than was fenoxaprop. Spray volumes, between 140 and 1120 L/ha, did not affect fenoxaprop efficacy; however, high volume applications (1120 L/ha) with floodjet nozzles were less effective than flat fan nozzle treatments in two of three tests. Added surfactant did not improve efficacy except with floodjet nozzles on a droughty site. No differences were observed between the water-based and the emulsifiable concentrate formulations of fenoxaprop. Fenoxaprop caused temporary phytotoxicity (≤20% reduction in turf quality) to established Kentucky bluegrass and perennial ryegrass.

Bromoxynil efficacy, uptake, translocation, and spray retention were investigated when bromoxynil was applied in conventional water volumes of 234 L ha−1 and in simulated sprinkler irrigation at 127 000 L ha−1 to common lambsquarters. Bromoxynil controlled common lambsquarters similarly regardless of water volume, whereas injury to spearmint, a tolerant crop, was greatest using low water volume. Spray retention was 18 and 38 times greater on common lambsquarters and spearmint, respectively, when bromoxynil was applied in 234 L ha−1 than 127 000 L ha−1. Two weeks after applying bromoxynil in 127 000 L ha−1 water volume, common lambsquarters dry weight was 60% of the nontreated check where only soil was treated but was 5% of the nontreated check where only leaves were treated. Roots of lambsquarters absorbed 22% of 14C-bromoxynil applied to hydroponic solution by 7 d, but only 2% was translocated to the shoots. Percent absorption and translocation of foliar-applied 14C-bromoxynil were 15 and 6% greater, respectively, from 0.0096 g L−1 than from a 1.2 g L−1 bromoxynil solution by 24 h after application. Uptake of bromoxynil was 13% greater through lower than upper leaf surfaces. These results suggest efficacy of bromoxynil applied in large spray volumes is, in part, due to root uptake, efficient foliar uptake and translocation, and uptake from lower leaf surfaces.

A plant-weighing procedure was used to measure the total mass of spray mixture intercepted by small whole corn and cotton plants. Mixtures of water and water plus crop oil concentrate or spreader–sticker were applied at spray volumes of 280 to 28,000 L/ha. The plants were weighed before and after passing under the spray and leaf areas, and shoot fresh and dry weights for each plant were measured. Spray deposition increased with spray volumes but not proportionally. Corn plants were larger than cotton plants and retained more spray per plant; however, cotton retained more spray per unit leaf area. The two adjuvants had similar effects on deposition, tending to increase it in corn and decrease it in cotton.

Surfactant concentrations from 0.0008 to 12.5% (w/w) in spray volumes from 19 to 475 L/ha were tested with and without rimsulfuron on giant foxtail. Both factors varied at 5-fold increments so treatments with equal surfactant concentrations and rates could be compared. As surfactant concentration increased from 0.0008 to 0.1%, rimsulfuron activity increased from less than 20% to more than 90% growth inhibition. This increase was dependent on surfactant concentration. As surfactant concentration increased from 0.5 to 12.5%, rimsulfuron activity decreased to less than 20% at all spray volumes. This decreased activity and the associated surfactant phytotoxicity was dependent on surfactant rate, not concentration. Thus rimsulfuron can be much less active when applied with too little or too much surfactant.

Reduced-rate herbicide strategies, which rely on treatment of small weed seedlings, are not effective under all situations. The consistency of reduced-rate treatments may be improved by adjustments in application variables. Field experiments were conducted at Kalispell, MT, during 1994 and 1995 to determine the effects of carrier volume on the efficacy of reduced-rate imazamethabenz applications for wild oat control in barley. Imazamethabenz was applied to two- and four-leaf wild oat plants at 0.26 and 0.52 kg ai/ha in carrier volumes of 75, 150, and 225 L/ha. Wild oat control generally increased as carrier volume increased, regardless of imazamethabenz rate or wild oat growth stage. However, increasing carrier volumes had a greater positive effect on wild oat control when imazamethabenz was applied to two-leaf vs. four-leaf wild oat seedlings. Barley yield was most affected by the duration of wild oat interference, with the greatest yield being observed with the earliest application. Barley yield tended to increase as carrier volume increased in 1 of 2 yr. These results indicate that wild oat control with imazamethabenz can be enhanced by increasing carrier volume, providing more consistent wild oat control from reduced imazamethabenz rates.

The effect of spray carrier volume on the antagonism of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} by bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] was investigated under greenhouse and field conditions. In the laboratory, the spray droplet overlap between components of a sequential spray application increased from 17 to 50% as carrier volume was increased from 94 to 374 L/ha, respectively. Carrier volume had a significant influence on treatments of sethoxydim alone and sethoxydim sequentially applied with bentazon, but not on the tank mixture of the two herbicides. Carrier volumes of 94 and 187 L/ha used to deliver sethoxydim alone and the sethoxydim/bentazon sequential treatment were superior to the use of 374 L/ha for the control of large crabgrass [Digitaria sanquinalis (L.) Scop. # DIGSA], fall panicum (Panicum dichotomiflorum Michx. # PANDI), and goosegrass (Eleusine indica Gaertn. # ELEIN). There was no difference in grass control between sethoxydim alone and the sequential treatment except at carrier volumes of 187 L/ha or more with which the sequential treatment was less effective. Rates of 0.06 and 0.11 kg ai/ha of sethoxydim were influenced more by changes in carrier volume than 0.22 kg/ha in both the alone and sequential treatments.

When herbicide concentration was constant, absorption of 14C-glyphosate increased with increasing droplet size (326 to 977 μm). Amount of 14C-glyphosate translocated away from the treated area, expressed as percent of absorbed, increased as droplet size decreased. Herbicide concentration of the droplet was more important than droplet number or droplet size in determining glyphosate absorption and translocation. Absorption and translocation increased with increasing herbicide concentration regardless of whether droplet size or number was altered in conjunction with herbicide concentration. This relationship explained why low spray volume (increased herbicide concentration) increased herbicide efficacy. The concentration gradient between droplet and leaf, rather than droplet coverage, was the primary mechanism responsible for the observed effect. Large droplets caused localized tissue injury, which may have caused decreased translocation.

Field experiments were conducted at three locations in Mississippi in 1995 and 1996 to evaluate labeled and alternative herbicides and herbicide combinations for weed desiccation prior to soybean harvest. Weeds evaluated included pitted morningglory, hemp sesbania, spotted spurge, common cocklebur, and sicklepod. Soybean yield and harvestable soybean losses were not affected by preharvest herbicide treatments, spray volume, or surfactant concentration. Soybean moisture was most consistently reduced by glufosinate compared to the untreated and other herbicides and herbicide combinations evaluated. Most desiccation treatments at Stoneville and Brooksville resulted in foreign material similar to the weed-free check. Glufosinate at 0.84, 1.1, and 1.4 kg ai/ha desiccated all weeds evaluated 90% or more with no differences among rates. The addition of 3.4 or 6.7 kg ai/ha sodium chlorate to 0.28 kg ai/ha paraquat, 1.1 and 2.2 kg ai/ha glyphosate, or 0.28 and 0.56 kg ai/ha oxyfluorfen increased desiccation of most weeds evaluated, with no difference between sodium chlorate rates. In some instances, reducing application volume from 281 to 94 L/ha improved pitted morningglory desiccation when 0.28 g/ha paraquat was applied alone. There were no differences between 0.25 and 0.50% (v/v) surfactant for most parameters evaluated.

Spray droplet size of water and paraffinic oil was affected by air pressure, nozzle type, and liquid flow rate when applied with an ultralow volume (ULV), air-assist sprayer. Volume median diameters of water were generally larger than oil at constant air pressure and liquid flow rate. Droplet size decreased as air pressure increased, but increased as liquid flow rate increased. Volume median diameters of water droplets ranged from 41 to 838 μm and from 16 to 457 μm with oil when atomized at air pressures ranging from 14 to 84 kPa. Relative spans ranged from 1.2 to 18.0 and 2.0 to 7.2 for water and oil, respectively.

Field experiments were conducted from 1993 to 1995 to evaluate control of annual weeds with glyphosate applied at rates of 560 to 2800 g ai/ha in spray volumes of 93 and 187 L/ha. Glyphosate controlled 100% of giant foxtail, fall panicum, redroot pigweed, and velvetleaf (in 1993) regardless of rate, spray volume, or application timing. Ivyleaf morningglory, velvetleaf, and common lambsquarters control was greater with glyphosate applied early POST than late POST. Ivyleaf morningglory, velvetleaf, and common lambsquarters control increased as glyphosate rate increased with both spray volumes. Velvetleaf control with glyphosate applied late POST was greater with glyphosate in 187 L/ha water compared with 93 L/ha water.

Weed management is often difficult and expensive in organic production systems. Clove oil is an essential oil that functions as a contact herbicide and may provide an additional weed management tool for use on organic farms. Burning nettle, purslane, and rye responses to 5, 10, 20, 40, and 80% v/v clove oil mixture applied in spray volumes of 281 and 468 L/ha were examined. Log-logistic curves were fitted to the nettle and purslane data to determine the herbicide dose required to reduce plant dry weight 50% (GR50) and 90% (GR90). A three-parameter Gaussian curve was fitted to the rye data. The GR50 and GR90 were largely unaffected by spray volume. Nettle dry weight was reduced by 90% with 12 to 61 L clove oil/ha, whereas 21 to 38 L clove oil/ha were required to reduce purslane biomass to the same level. Rye was not effectively controlled by clove oil. Clove oil controls broadleaf weeds at high concentrations, but its cost makes broadcast applications prohibitive, even in high-value vegetable production systems.

Research was conducted in 2010 and 2012 to determine the effect of simulated drift of nicosulfuron on growth and yield of grain sorghum. Herbicide rates represented 25, 12.5, and 6.3% of the use rate of nicosulfuron at 52 g ai ha−1. Nicosulfuron was applied in a constant carrier volume of 224 L ha−1 where herbicide concentration decreased with reduction in rate, and in carrier volumes of 56, 28, and 14 L ha−1 proportional to the 25, 12.5, and 6.3% herbicide rates, respectively. In 2010, grain sorghum injury and yield were greater when nicosulfuron was applied in constant compared to proportional carrier volume. Grain sorghum injury and plant height reduction increased with increasing nicosulfuron rate when averaged across carrier volume both years. In 2012, there was a greater reduction in grain sorghum yield from nicosulfuron applied in proportional carrier volume. These data indicate that simulated drift of nicosulfuron onto conventional grain sorghum causes significant height and yield reduction even at the lowest herbicide rate tested, and the effect of carrier volume may be influenced by seasonal rainfall.

Sprayer applicator-controlled variables, such as nozzle selection and spray volume, will become increasingly important for making labeled POST applications of dicamba in next-generation cropping systems. A field experiment was conducted in 2013 and 2014 at the Northeast Research and Extension Center in Keiser, AR. Tank mixtures of Engenia (a new form of dicamba), glyphosate, glufosinate, and S-metolachlor were applied with TeeJet AIXR, AITTJ60, and TTI nozzles. Two nozzle sizes, 11003 and 11006, were used to vary spray volume from 94 L ha−1 to 187 L ha−1, respectively. For barnyardgrass, a significant decrease in control was observed when spray volume was reduced for glyphosate + dicamba in 2013. In 2014, an overall decrease in control was observed for the TTI nozzle when spray volume was reduced to 94 L ha−1, averaged across all herbicide treatments. The addition of the product S-metolachlor to glyphosate + glufosinate + dicamba significantly reduced the droplet spectra for all nozzle types. For example, adding S-metolachlor into the tank-mix decreased the volume median diameter (Dv50) for the TTI nozzle at 187 L ha−1 spray volume from 789 μm to 570 μm. The results from this research demonstrate that using low spray volume and coarser nozzles could reduce efficacy of the herbicides on the weed species evaluated. Nozzle selection and spray volume have key roles in maximizing efficacy of POST applications in dicamba-resistant crops. Additionally, evaluating droplet spectra of potential dicamba-containing tank-mixtures is critical for producing the desired droplet size to minimize off-target movement.

Herbicide efficacy, coverage, and retention were evaluated for spray applied through Drift Guard, Turbo TeeJet, AI TeeJet, and TurboDrop drift-reducing nozzles compared to a conventional flat-fan nozzle. Percentage spray coverage detected on water-sensitive cards was greater for conventional and Drift Guard nozzles than for Turbo TeeJet, AI TeeJet, and TurboDrop nozzles. Spray without adjuvants was retained better by redroot pigweed for treatments applied with conventional and Drift Guard nozzles than Turbo TeeJet, AI TeeJet, and TurboDrop nozzles. However, spray with adjuvants was retained similarly for all nozzle types when averaged over spray adjuvant and two weed species. The efficiency of spray retention was greater for spray applied in 47 than in 190 L/ha spray volume for all nozzles. Paraquat and glyphosate, representing contact and translocated herbicides, respectively, provided similar grass species control for all nozzle types, regardless of spray volume. Paraquat and glyphosate were also equally or more effective in 47 compared to 190 L/ha spray volume.