Spray Retention Research Articles

Surfactant and salt affect glyphosate retention and absorption

SummaryThe influence of nonylphenoxy surfactants and glyphosate salt formulation on spray retention, phytotoxicity and [14C]glyphosate uptake was investigated in wheat (Triticum aestivum L). and Kochia scoparia L. The amount of spray retained, and uptake of [14C]glyphosate increased with increasing hydrophilic‐lipophilic balance (HLB) value of surfactants. The volume of spray delivered to the plant treatment area and retained by wheat and K. scoparia plants increased with increasing surfactant HLB values, but this only partly accounted for the higher spray retention. Spray retention by leaves of plants was not affected by calcium chloride, either alone or with ammonium sulphate in the glyphosate spray solution. [14C]Glyphosate absorption by wheat and K. scoparia was reduced by calcium chloride alone, but not in mixtures with ammonium sulphate, regardless of surfactant. Phytotoxicity and uptake of glyphosate salt formulations for wheat was: isopropylamine > ammonium > sodium > calcium; these results indicate that the surfactant selected is important to maintain glyphosate efficacy and that sodium and calcium cations antagonize glyphosate by forming salts that are absorbed less than commercial isopropylamine formulations.

Bentazon Spray Retention, Activity, and Foliar Washoff in Weed Species

Greenhouse studies were conducted to investigate the effects of adjuvant and rainfall on bentazon spray retention, efficacy, and foliar washoff in hemp sesbania, sicklepod, smooth pigweed, and velvetleaf. Bentazon was applied at 0.28 to 2.24 kg ai/ha with Agri-Dex, a crop oil concentrate (COC) or Kinetic, an organiosilicone-nonionic surfactant blend (OSB) when weeds were at the three- to five-leaf stage. Plants were subjected to 2.5 cm simulated rainfall for 20 min at 1 and 24 h after application of bentazon. Shoot fresh weight reduction assessed 2 wk after treatment was similar with either adjuvant on velvetleaf and smooth pigweed. OSB enhanced bentazon efficacy in hemp sesbania and sicklepod as compared to COC. Rainfall at 1 h after application generally reduced bentazon activity in all weeds. OSB maintained bentazon activity in hemp sesbania when subjected to rainfall at 1 h after application as compared to COC. Overall, bentazon spray retention on plants was 9 to 550% higher with OSB as compared to COC among the species at 1 h after application. Amount of bentazon residue washed off from the foliage by rainfall within a weed species was relatively similar for both adjuvants except in smooth pigweed and ranged from 39 to 98% among the four weed species at 1 h after application. OSB exhibited specificity for certain weed species and the potential to minimize bentazon spray reaching the soil by increasing deposition.

FLUID VELOCITY AND SHEAR IN ELLIPTIC-ORIFICE SPRAY NOZZLES

With new pest control and bioregulating formulations under development and coming into use to improve spray retention and coverage, concerns have arisen about possible adverse effects on spray solutions due to fluid shear occurring in nozzles. Mathematical models were developed for velocity and shear-rate distributions for incompressible liquid flow through fan-pattern spray nozzles having approximately elliptic outlet orifices. The velocity distribution model was verified with phase/Doppler particle analyzer measurements and computational fluid dynamic simulations. A mean fluid velocity section of the model predicted the axial flow velocity to be 29.03 m/s for an 8002 brass fan-pattern nozzle with 276 kPa operating pressure, compared with a mean measured value of 29.85 m/s. With the shear rate model, it was found that use of an older equivalent-circle model resulted in significant underestimates of shear rates for fan-pattern nozzles. Liquid shear rates at the orifice wall varied with position, and were estimated to fall in the range 1.2 × 105 to 7 × 105 s−1 for the spray nozzles studied, depending on nozzle characteristics and operating pressure over a range of 138 to 414 kPa.

Basis for the Differential Response of Quackgrass (Elytrigia repens) Biotypes to Primisulfuron

Factors accounting for the differential response of five quackgrass biotypes to primisulfuron were compared. Previous field and greenhouse experiments had identified a biotype from Montpelier, OH, as being less susceptible to primisulfuron than biotypes from Amherst, MA; Mahnomen, MN; Fargo, ND; and State College, PA. Differences in shoot, root, and rhizome fresh weights and rhizome bud numbers did not account for the reduced susceptibility of the Montpelier, OH, biotype to primisulfuron. Spray retention was lower in biotypes from OH and MA compared to the others. Absorption of14C following14C-primisulfuron application was greater in the Amherst, MA, biotype compared to the others. Only 29% of absorbed14C was present as primisulfuron in the Montpelier, OH, biotype versus 41 to 45% in the other biotypes 72 h after application. The amount of primisulfuron present in the Montpelier, OH, biotype 72 h after application was less than half the amount present in the other four biotypes due to reduced spray retention and faster metabolism. These factors combined explain lower susceptibility of the Montpelier, OH, biotype to primisulfuron.

Effect of an organosilicone surfactant on spray drop adhesion and retention by pea (<i>Pisum sativum</i>) leaf surfaces

Effect of an organosilicone surfactant on spray drop adhesion and retention by pea (<i>Pisum sativum</i>) leaf surfaces

Fate of Fenoxaprop-Ethyl Applied to Moisture-Stressed Smooth Crabgrass (Digitaria ischaemum)

Investigations of smooth crabgrass growth and fenoxaprop-ethyl retention, foliar penetration, translocation, and metabolism were conducted at various soil moisture levels using a polyethylene glycol (PEG) semipermeable membrane system. The activity of fenoxapropethyl was significantly reduced at higher levels of moisture stress and this antagonistic effect was greater with increased duration of water deficit following herbicide application. Fenoxaprop-ethyl spray retention decreased linearly (23% total reduction) as soil matric potential (Ψm) decreased from −0.01 to −0.1 MPa. Foliar penetration and translocation of14C-fenoxaprop-ethyl applied on the third true leaf were not affected by level or duration of moisture stress. Only 2% of the absorbed radioactivity was translocated out of the treated leaf for each moisture stress level and duration. As the soil Ψm decreased (−0.01 to −1.0 MPa) the relative levels of fenoxaprop-ethyl increased by 76 and 65% after a 48- and 96-h postapplication moisture stress period, respectively. In contrast, fenoxaprop acid decreased by 59 and 44% after 48 and 96 h of moisture stress, respectively. The relative level of fenoxaprop acid was linearly correlated to the antagonistic effect on shoot dry weight. These results suggest that decreased spray retention and, particularly, alterations in fenoxaprop-ethyl metabolism contribute to reduced fenoxaprop-ethyl activity observed in moisture-stressed smooth crabgrass.

Efficacy, Site of Uptake, and Retention of Bromoxynil in Common Lambsquarters with Conventional and Sprinkler Application

Bromoxynil efficacy, uptake, translocation, and spray retention were investigated when bromoxynil was applied in conventional water volumes of 234 L ha−1and in simulated sprinkler irrigation at 127 000 L ha−1to 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−1than 127 000 L ha−1. Two weeks after applying bromoxynil in 127 000 L ha−1water 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% of14C-bromoxynil applied to hydroponic solution by 7 d, but only 2% was translocated to the shoots. Percent absorption and translocation of foliar-applied14C-bromoxynil were 15 and 6% greater, respectively, from 0.0096 g L−1than from a 1.2 g L−1bromoxynil 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.

Influence of wetting agents on the foliar uptake and herbicidal activity of glufosinate

AbstractThe influence of four different wetting agents on the foliar retention, uptake and herbicidal activity of the glutamine synthetase inhibitor, glufosinate, was examined in growth‐chamber experiments on barley (Hordeum vulgare L. cv Roland) and barnyard grass (Echinochloa crus‐galli (L.) P.B.) as test species.The non‐formulated monoammomum salt, glufosinate‐ammonium, was applied as a spray, either alone or mixed with a wetting agent. The dose rates of herbicide and wetting agent were 0.5 g a.i. litre−1 and 2.0 g litre−1, respectively, on barnyard grass, and 2.0 g a.i. litre−1 and 60 g litre−1, respectively, on barley. Herbicide damage, rated 10 days after spraying, was greatest when glufosinate was used with a sodium C12/C14‐alcohol‐diglycolether sulfate (FAEO‐sulfate) and least with polyoxyethylene (POE)(8) tridecyl ether; intermediate effectiveness was obtained with a combination of herbicide and a POE(15) tridecyl ether or POE(15)‐tallow amine.The activity of the target enzyme, glutamine synthetase, measured 2 h after spraying, was reduced most when FAEO‐sulfate was present and least with POE(8) tridecyl ether.The behaviour of the glufosinate wetting agent solutions on plant foliage was analysed by measurements of spray retention, droplet contact angles and foliar uptake of [14C]glufosinate. The results led, for both grass species, to the conclusion that differential ability of the wetting agents to enhance the permeation of glufosinate from the leaf surface deposit into the leaf tissue was the main factor responsible for the differences in herbicidal effectiveness of the glufosinate/wetting agent combinations used in this study.

Influence of Adjuvants on the Efficacy, Absorption, and Spray Retention of Primisulfuron

The effect of methylated seed oil (MSO), the organosilicone adjuvant DC-X2-5394, and ammonium sulfate on the efficacy, absorption, and spray retention of primisulfuron applied alone or with atrazine, dicamba, and bentazon to shattercane and giant foxtail was evaluated. Primisulfuron efficacy on both species was reduced by the three tank-mix combinations. Atrazine antagonism was not explained by decreases in foliar absorption and/or spray retention. Reductions in primisulfuron absorption and/or foliar spray retention appeared to cause bentazon antagonism on both weeds and dicamba antagonism on shattercane. MSO, DC-X2-5394, and ammonium sulfate completely reversed dicamba and bentazon antagonism on shattercane and partially reversed bentazon antagonism on giant foxtail by increasing foliar absorption and/or spray retention. Compared with non-ionic surfactant, MSO and DC-X2-5394 consistently increased giant foxtail control with primisulfuron by increasing foliar absorption and/or spray retention.

Total leaf areas of single trees of Eucalyptus grandis estimated from transmittances of the sun's beam

Total leaf areas of isolated plants can be estimated from the transmittance of the direct beam of the sun. Leaf area is obtained by integrating the logarithm of transmittances over an area which encompasses the shadow of a plant. Details of the theory and procedures are given. A central assumption of the method is that projections of the foliage are arranged randomly on an area about 10 times the area of leaves. Experiments with small trees grown in the field and in pots showed that total leaf areas for E. grandis trees estimated from transmittances were linearly correlated with measurements from a planimeter, over a range of leaf areas from 0.06–1.6 m 2 per tree, and were, on average, 14% lower. The lower values were probably caused by departures from the random distribution which was assumed theoretically. Because of its operational simplicity, acceptable accuracy and theoretical basis, the procedure is believed to be useful for studies of developing trees in plantations in the early stages of growth, for ecological studies in sparsely vegetated communities, and for estimates of surface area when examining spray retention and rainfall interception by isolated plants.

A partitioned energy transfer model for spray impaction on plants

Of the processes active in foliar spray application of pesticidal and biologically active compounds in agriculture, impaction and deposit formation have been relatively neglected topics of investigation. Experimental research on spray-dynamic phenomena at the plant interface shows that rebound of droplets from some plant surfaces is a significant factor limiting effective application and retention. An energy transfer model was developed which predicts probable reflected velocity factors, or coefficients of restitution, for the first-impact rebound of droplets from a plant surface. The model, based on the principle of equipartition of energy as a limiting case, requires uniform distribution of incoming kinetic energy, on the average, among the dimensions of energy transfer modes involved. Energy transfer modes identified include droplet and plant-surface elastic deformation, impulse or shock, and plant-surface alteration. Available energy from elastic deformations is partitioned among droplet translation, rotation, oscillatory and internal energies when rebound occurs. The model will help determine the most effective ways to modify energy transfer in order to limit droplet rebound and improve spray retention.

Effect of low temperatures on 2,4‐D behaviour in maize plants

Summary:The foliar surface of 4‐leaf maize plants was found to be poorly wettable and retained 106 μl g−1 dry matter when sprayed with a U46D (2,4‐D formulation) blank. The third leaf retained 141 μl g−1. A 7‐day cold spell (17/9°C) increased retention per unit dry matter by 53% (135% on the third leaf). Cold stress lowered epicuticular wax quantity by 29% on the third leaf. Contact angles of formulated 2,4‐D lay between 115 and 125° and were not significantly affected by cold stress. 2,4‐D rapidly entered into maize third leaf (66% in 24 h) but migration from it was less than 1.5%. 2,4‐D was readily degraded in maize (80% in 72 h). The most abundant metabolite was probably an ester conjugate; little of the hydroxy derivatives were found. Cold stress reduced 2,4‐D degradation, and 72 h after treatment the amount of undegraded 2,4‐D was 78% higher in cold‐stressed maize plants. It was concluded that 2,4‐D selectivity in maize results from low spray retention per unit dry matter and active degradation of penetrated herbicide. Cold stress affects both factors.

Influence of Surfactants and Plant Species on Leaf Retention of Spray Solutions

Spray solutions containing a cationic or a nonionic surfactant were applied to six plant species at a broad range of concentrations. The species investigated were three weeds (black nightshade, chamomile, and quackgrass) and three crops (winter wheat, pea, and tomato). The microroughness of the leaf surface as revealed by scanning electron microscopy appeared to be a relevant retention-determining factor. Plant species with crystalline epicuticular waxes (winter wheat, pea, and quackgrass) retained much less spray solution than the other species, which are characterized by a smooth cuticular surface. The two surfactants enhanced retention on species with a reflective surface, whereas retention on black nightshade, chamomile, and tomato was hardly influenced by addition of surfactants. The two surfactants had a similar influence on the retention. Surfactant at 1% (wt/v) enhanced retention on pea, winter wheat, and quackgrass by factors of twenty, six, and four, respectively, compared with retention without surfactant. A linear relation between retention and logarithm of surfactant concentration was observed. Retention of spray drops was related not to equilibrium surface tension of the spray solution but rather to dynamic surface tension.

Mechanism of Glyphosate Tolerance in Birdsfoot Trefoil (Lotus corniculatus)

The mechanism of glyphosate tolerance was investigated in nine birdsfoot trefoil selections that exhibited a threefold difference in glyphosate tolerance. Single-stemmed ramets (vegetative clones) established from the nine selections were used to evaluate tolerance to glyphosate, spray retention, and14C-glyphosate absorption and translocation in growth chamber experiments. The tolerance of greenhouse-grown ramets correlated with the tolerance of field-grown plants, indicating that tolerance was not a function of plant size or affected by environment. The nine selections differed in spray retention and14C-glyphosate translocation but not in glyphosate absorption. The differences in retention and translocation were not correlated with the level of glyphosate tolerance but could contribute to the tolerance of an individual plant. The specific activity of 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS) (EC 2.5.1.19) ranged from 1.3 to 3.5 nmol min−1mg−1protein among the nine selections assayed and was positively correlated with plant tolerance level. These results indicate that the primary mechanism of glyphosate tolerance in birdsfoot trefoil is based on the level of EPSPS activity.

Pre‐treatment environmental effects on the uptake, translocation, metabolism and performance of fluazifop‐butyl in Elymus repens

SummaryThe performance of fluazifop‐butyl against Elymus repens (L.) Gould was significantly influenced by the environmental conditions in which the plants had grown prior to treatment as follows: soil moisture deficit (greatest reduction of herbicide performance) > cool temperatures > low light intensity. The level of control under conditions in which none of these factors was reduced (so‐called ‘standard’ conditions) was similar to that observed for‘low light’regime plants. Significant effects of environment on spray retention, foliar uptake and amounts of herbicide translocated to the roots and rhizomes were observed. The lowest rates of herbicide uptake were found with plants grown under cool conditions, the greatest amount of basipetal herbicide translocation being associated with low light intensities. Rates of herbicide de‐esterification were much lower in plants grown under low light intensities, cool temperatures, or soil moisture deficits than in those plants grown under the ‘standard’ conditions. This result was confirmed by studies of herbicide deesterification using cell‐free leaf homogenates.

The Impact of Adjuvants on Herbicide Antagonism

Adjuvants are used to improve spray delivery, to increase spray retention on weed foliage, and to enhance foliar penetration by postemergence herbicides for increased herbicide efficacy. Numerous factors govern adjuvant efficacy, including the specific herbicide, plant species, and environmental conditions. Adding superior surfactants as adjuvants to a sethoxydim tank mix with Na-bentazon may overcome the Na-bentazon antagonsim of sethoxydim activity by facilitating increased sethoxydim absorption and by masking the antagonism similar to increasing the sethoxydim rate. Herbicides such as Na-bentazon contribute alkaline or alkaline earth cations that can form salts of a weakly acidic herbicide such as sethoxydim that are not absorbed readily by the plant. Adding abundant ammonium from ammonium sulfate or other sources may prevent and/or may overcome this antagonism.

Effects of application methods, spray volumes, pressures and herbicide rates on weed control in spring cereals

Herbicides were sprayed in spring cereals with conventional and low pressure hydraulic flat-fan spray nozzles and rotary atomizers. The biological effects were measured on weeds and oats. In addition, some spray retention studies were performed. Conventional flat-fan spray nozzles at a spraying pressure of 2 or 4 bar (200 or 400 kPa) gave the best effect. There was no difference in effect between spray volumes of 125 1/ha and 250 1/ha. In most field situations, 200 kPa and 125 1/ha should be preferred. However, when the spray volume is reduced from 250 to 125 1/ha, the droplet size decreases and the drift hazard increases. Where great care has to be taken, the use of conventional flat-fan spray or low-pressure nozzles at 100 kPa and 250 1/ha may be a compromise between effect and safety.

Plant Responses to Haloxyfop as Influenced by Water Stress

Green foxtail [Setaria viridis(L.) Beauv. # SETVI] and proso millet [Panicum miliaceum(L.) #PANMI] growing under high water stress for 3 days before + 3 days after foliar applications of the methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} developed less herbicide injury than plants growing under low water stress. There was a 32% reduction in the retention of haloxyfop sprays by proso millet when growing under high water stress than when growing under low water stress. Haloxyfop spray retention by green foxtail was not affected by the degree of water stress. The translocation of14C out of14C-haloxyfop-treated leaves was significantly greater in plants of both species when growing under low water stress than when growing under high water stress. The conversion of 98% of the absorbed14C-haloxyfop-methyl to14C-haloxyfop and unidentified polar metabolites occurred in both species within 12 h of application. The green foxtail growing under low water stress contained greater concentrations of14C-haloxyfop than did plants growing under high water stress. Levels of14C-haloxyfop were the same in proso millet growing under high and low water stress. The reduced injury of green foxtail and proso millet growing under high water stress from postemergence sprays of haloxyfop can be attributed to a reduction in herbicide translocation in both species, plus a reduction in spray retention by proso millet or changes in the metabolism of the herbicide in green foxtail, which results in a reduction in the concentration of haloxyfop.

Studies into the differential activity of the hydroxybenzonitrile herbicides: II. Uptake, movement and metabolism in two contrasting species

Uptake, movement, and metabolism of unformulated ioxynil and bromoxynil salts were investigated in Matricaria inodora and Viola arvensis. The morphology of these two species did not give rise to different spray retention and contact angles. After 7 days, uptake of [ 14C]ioxynil-Na reached 8.26% of applied 14C activity in M. inodora and 16.77% of that in V. arvensis compared with 1.54 and 3.83%, respectively, for [ 14C]bromoxynil-K. Over 98% of the 14C activity detected in the plant after 7 days remained in the treated leaves of V. arvensis following [ 14C]ioxynil-Na treatment. However, 8.7% of the 14C activity detected in [ 14C]ioxynil-Na-treated M. inodora was recovered from the apex and developing leaves reflecting a greater translocation. [ 14C]Bromoxynil-K was more mobile in both species and after 7 days 87.5 and 91.39% were detected in the treated leaves of M. inodora and V. arvensis, respectively. In both species the majority of translocated 14C activity was recovered from the apex and developing leaves. Up to 20% of the applied [ 14C]ioxynil-Na and [ 14C]bromoxynil-K was not detected within the treated plant. Extraction of treated plants revealed no detectable metabolic breakdown of ioxynil-Na to halogenated derivatives in either species. However, metabolic breakdown of bromoxynil-K was apparent in V. arvensis. No significant root exudation was detected when [ 14C]ioxynil-Na and [ 14C]bromoxynil-K were applied to hydroponically grown S. media and V. arvensis. Losses of 14C activity were due to herbicide volatility or degradation to volatile products on the leaf surface.

RESPONSE OF ONION (Allium cepa) TO OXYFLUORFEN DURING EARLY SEEDLING DEVELOPMENT

The response of onion (Allium cepa L.) to postemergence applications of oxyfluorfen during early seedling development was measured in growth room experiments. Tolerance to oxyfluorfen increased more than 70-fold from the late loop to the two fully developed leaf stage. Field and growth room experiments were also conducted to determine the relationship of spray retention and epicuticular wax on the tolerance of onion seedlings to the herbicide. In general, there was a progressive decrease in spray retention and a corresponding increase in epicuticular wax per unit dry weight as plant age increased. Spray retention in the field was approximately twice as great as in the growth room. The amount of epicuticular wax on the leaf surfaces of the onions was about equivalent under the two growing conditions. A significant decrease in epicuticular wax per unit dry weight between the late one-leaf and late two-leaf stages occurred under both field and growth room conditions, while tolerance to the herbicide continued to increase during the same period.Key words: Onions, oxyfluorfen, ED50, spray retention, epicuticular wax