Organosilicone Surfactant Research Articles

Characterization of synthetic and commercial trisiloxane surfactant materials

AbstractThe organosilicone surfactant Silwet L‐77® (L‐77), used as an agrochemical adjuvant, is a mixture comprised predominantly of [(CH3)3SiO]2(CH3)Si(CH2)3(OCH2CH2)nOCH3 oligomers (n = 3–16, average n ≈ 7.5). The commercially available L‐77 mixture was purified by reversed‐phase high‐performance liquid chromatography (HPLC) to obtain individual trisiloxane surfactant components. Pure oligomers (n = 3, 6 and 9) were also synthesized. Synthesis was achieved by hydrosilylation of monomeric ethoxylate monomethyl ether starting reagents. Pure hexa‐ and nona‐ethylene glycols were produced by condensation of smaller oligomers.Atmospheric‐pressure ionization mass spectrometry (MS) methods were used to characterize fully the commercial L‐77 product and synthesized or isolated components. The application of Fourier‐transform ion cyclotron resonance MS and online HPLC–electrospray ionization MS techniques to the analysis of this surfactant are described here. The application of these analytical techniques also enabled elucidation of the synthetic by‐products present in the commercial formulation.In addition, physico‐chemical properties specific to agrochemical uses, such as droplet spread areas on plant foliage and surface tension for the different oligomer solutions, are also reported. Copyright © 2004 John Wiley & Sons, Ltd.

Myrothecium verrucaria for Control of Annual Morningglories in Sugarcane1

Conidia of Myrothecium verrucaria, sprayed in an aqueous phase–paraffinic crop oil emulsion (1:1 v/v) at 470 L/ha, controlled red, ivyleaf, smallflower, and tall morningglory plants (three- to five-leaf stage) by causing severe necrotic injury to leaves and stems. Conidia were not efficacious if applied in an aqueous carrier without oil. When applied in the field as directed postemergence treatments to sugarcane, a concentration of 4 × 108 conidia/ml generally provided > 90% death of morningglory, comparable with the atrazine standard at 2.2 kg ai/ha, and did not cause significant crop injury. Conidia produced on potato dextrose agar or rice flour slurry were about equally effective. When killed by autoclaving, conidia continued to be efficacious, indicating that the symptoms produced by the fungus were not primarily caused by infection. A high performance liquid chromatography analysis of filtrates from the fungal growth media or of harvested conidia showed the presence of several macrocyclic trichothecenes (MT), some known to be phytotoxins. These included verrucarin A and H, roridin A and H, and isororidin E for filtrates and verrucarin A and roridin A for conidia. However, only trace amounts of MT were detected in leaves of treated morningglory plants at 24 h after treatment and none at 48 and 96 h even though the fungus was isolated from leaves up to 14 d after treatment. Further study is needed to identify the causal agents responsible for the phytotoxicity produced by M. verrucaria and to assess potential of this organism as a mycoherbicide.Nomenclature: Atrazine; Myrothecium verrucaria (Albertini & Schwein.) Ditmar:Fr.; ivyleaf morningglory, Ipomea hederacea (Jacq.) #3 IPOHE; red morningglory, Ipomea coccinea (L.) # IPOCC; smallflower morningglory, Jacquemontia tamnifolia (L.) Griseb. # IAQTA; tall morningglory, Ipomea purpurea (L.) Roth # PHBPU; sugarcane, Saccharum sp. hybrids ‘CP 72-370’.Additional index words: Biological weed control, macrocyclic, mycoherbicide, mycotoxins, trichothecenes.Abbreviations: DAT, days after treatment; HPLC, high performance liquid chromatography; IE, invert emulsion (water-in-oil); IPA, isopropyl alcohol; MT, macrocyclic trichothecenes; PDA, potato dextrose agar; POST, postemergence; RF, rice flour; SE, standard emulsion (oil-in-water); SIL, organosilicone surfactant; ST, sucrose–Tween 80 solution.

Efficacy of Silwet L-77 Against Several Arthropod Pests of Table Grape

Silwet L-77, an organosilicone surfactant, was applied to several arthropod pests of California table grapes. Eggs of grape mealybug, Pseudococcus maritimus (Ehrhorn), and omnivorous leafroller, Platynota stultana Walsingham, were tolerant to 0.1, 0.25, and 0.5% treatment solutions; however, eggs of Pacific spider mite, Tetranychus pacificus McGregor, were highly susceptible with mortality >99.4% (0.1% Silwet L-77). Mortality of immature and adult stages of cotton aphid (Aphis gossypii Glover), Western flower thrips (Frankliniella occidentalis Pergande), and Pacific spider mite (Tetranychus pacificus McGregor) was ≥93.8, ≥98.5, and ≥99.4% for 0.1, 0.25, and 0.5% Silwet L-77, respectively. Grape mealybug crawlers had 100% mortality when treated with 0.5 and 1.0% Silwet L-77 solutions; however, mortality was only 6.7% when 0.1% Silwet L-77 was applied. ‘Thompson Seedless’ table grapes were not damaged when treated with up to 1% Silwet L-77; however, grapes treated with the 0.5 and 1.0% solutions appeared wet after removal from cold storage because of the effect of the surfactant spreading the water condensation. Grapes dried with the normal bloom on the berries when they reached room temperature.

Efficacy of Silwet L-77 against several arthropod pests of table grape.

Silwet L-77, an organosilicone surfactant, was applied to several arthropod pests of California table grapes. Eggs of grape mealybug, Pseudococcus maritimus (Ehrhorn), and omnivorous leafroller, Platynota stultana Walsingham, were tolerant to 0.1, 0.25, and 0.5% treatment solutions; however, eggs of Pacific spider mite, Tetranychus pacificus McGregor, were highly susceptible with mortality >99.4% (0.1% Silwet L-77). Mortality of immature and adult stages of cotton aphid (Aphis gossypii Glover), Western flower thrips (Frankliniella occidentalis Pergande), and Pacific spider mite (Tetranychus pacificus McGregor) was > or = 93.8, > or = 98.5, and > or = 99.4% for 0.1, 0.25, and 0.5% Silwet L-77, respectively. Grape mealybug crawlers had 100% mortality when treated with 0.5 and 1.0% Silwet L-77 solutions; however, mortality was only 6.7% when 0.1% Silwet L-77 was applied. 'Thompson Seedless' table grapes were not damaged when treated with up to 1% Silwet L-77; however, grapes treated with the 0.5 and 1.0% solutions appeared wet after removal from cold storage because of the effect of the surfactant spreading the water condensation. Grapes dried with the normal bloom on the berries when they reached room temperature.

Correcting Iron Deficiency in Calibrachoa Grown in a Container Medium at High pH

The objective was to evaluate and compare foliar spray and soil drench application methods of iron (Fe) for correcting Fe deficiency in hybrid calibrachoa (Calibrachoa × hybrida) grown in a container medium at pH 6.9 to 7.4. Untreated plants showed severe chlorosis and necrosis, stunting, and lack of flowering. An organosilicone surfactant applied at 1.25 mL·L-1 (0.160 fl oz/gal) increased uptake of Fe from foliar applications of both ferrous sulfate (FeSO4) and ferric ethylenediamine tetraacetic acid (Fe-EDTA). Foliar sprays at 60 mg·L-1 (ppm) Fe were more effective when Fe was applied as Fe-EDTA than FeSO4. Increasing Fe concentration of foliar sprays up to 240 mg·L-1 Fe from Fe-EDTA or 368 mg·L-1 Fe (the highest concentrations tested) from ferric diethylenetriamine pentaacetic acid (Fe-DTPA) increased chlorophyll content compared with lower spray concentrations, but leaf necrosis at the highest concentrations may have been caused by phytotoxicity. Drenches with ferric ethylenediaminedi(o-hydroxyphenylacetic) acid (Fe-EDDHA) at 20 to 80 mg·L-1 Fe were highly effective at correcting Fe-deficiency symptoms, and had superior effects on plant growth compared with drenches of Fe-DTPA at 80 mg·L-1 Fe or foliar sprays. Efficacy of Fe-DTPA drenches increased as concentration increased from 20 to 80 mg·L-1 Fe. An Fe-EDDHA drench at 20 to 80 mg·L-1 Fe was a cost-effective option for correcting severe Fe deficiency at high medium pH.

Evaluation of Curvularia intermedia (Cochliobolus intermedius) as a potential microbial herbicide for large crabgrass (Digitaria sanguinalis)

Abstract Curvularia intermedia, anamorph of the fungus Cochliobolus intermedius, was isolated from diseased crabgrass (Digitaria sp.) plants and evaluated in greenhouse studies for its potential as a microbial herbicide for control of large crabgrass (Digitaria sanguinalis). The objectives were to evaluate the host range of the fungus and to determine mortality and dry-weight reductions of large crabgrass as influenced by concentrations of inoculum and Silwet L-77 (an organosilicone surfactant), post-inoculation dew temperature, and post-inoculation dew duration. In addition, control of large crabgrass growing in mixed stands with soybeans was evaluated. Ninety to 100% control of large crabgrass, as indicated by mortality and dry-weight reduction, was obtained when inoculum concentrations were ⩾1×106 conidia/ml, Silwet L-77 concentrations were ⩾0.1% (v/v), and dew periods were ⩾10 h (20–35 °C). Forty plant species in 10 families were screened against C. intermedia in host-range studies. Species that exhibited mortality and/or significant dry-weight reductions due to fungal inoculations included: redroot pigweed (Amaranthus retroflexus), beet (Beta vulgaris), chenopodium (Chenopodium amaranticolor), wild oat (Avena fatua), broadleaf signalgrass (Brachiaria platyphylla), bermudagrass (Cynodon dactylon), large crabgrass, barnyardgrass (Echinochloa crus-galli), red rice (Oryza sp.), green foxtail (Setaria viridis), shattercane (Sorghum bicolor), johnsongrass (Sorghum halepense), one cultivar of grain sorghum (Sorghum vulgare), and two cultivars of corn (Zea mays). No mortality or significant dry-weight reductions were noted for peanut (Arachis hypogaea), soybean (Glycine max), cotton (Gossypium hirsutum), centipedegrass (Eremochloa ophiuroides), St. Augustinegrass (Stenotaphrum secondatum), zoysiagrass (Zoysia sp.), or 23 other species. When C. intermedia was applied to mixed plantings of soybeans and large crabgrass, 80–96% reductions in dry weight occurred for large crabgrass seedlings. No significant dry-weight reductions were observed for the soybean plants when compared to the control plants. These results indicate that C. intermedia could be a potential microbial herbicide for control of large crabgrass in crops such as soybean, cotton, and peanut. Additional studies are needed to assess the potential for use of C. intermedia for control of Digitaria spp. in turf grasses such as centipedegrass, zoysiagrass, and St. Augustinegrass that exhibited resistance to the fungus.

Influence of sugars on the foliar uptake of bentazone and glyphosate

The effect of sugars on the uptake of bentazone and glyphosate into bean (Vicia faba) and wheat (Triticum aestivum) foliage was studied The addition of 05 glucose or sucrose significantly increased the uptake of bentazone into bean and wheat leaves This effect was also observed in the presence of a surfactant especially in wheat Glucose and sucrose also improved the uptake of glyphosate into wheat leaves especially in combination with surfactants of low ethylene oxide content When used at 2 concentration both sugars completely overcame the antagonistic effect of an organosilicone surfactant (Silwet L77) on glyphosate uptake into wheat leaves The results are discussed in relation to the solute dose on the leaf surface as influenced by surfactants and sugars

Assessment of Pseudomonas syringae pv. tagetis as a biocontrol agent for Canada thistle

Abstract Growth chamber and field experiments were conducted to assess the potential of Pseudomonas syringae pv. tagetis (Pst) as a biocontrol agent for Canada thistle. Silwet L-77, an organosilicone surfactant, was required to facilitate Pst penetration into Canada thistle leaves. Growth chamber experiments indicated that maximum Pst populations inside leaves were obtained with a Silwet L-77 concentration of 0.3% (v/v) or greater. High Pst populations (109 colony-forming units [cfu] per gram fresh weight) were found in leaves 48 h after treatment with 108 or 109 cfu ml−1 Pst plus Silwet L-77 (0.3%, v/v). In growth chamber experiments, foliar application of Pst (109 cfu ml−1) plus Silwet L-77 (0.3%, v/v) on 4- to 5-wk-old Canada thistle reduced shoot dry weight by 52% (measured 14 d after treatment) and chlorophyll content of emerging leaves by 92% (measured 10 d after treatment). In field trials conducted in 1999 and 2000, Pst (109 cfu ml−1) plus Silwet L-77 (0.3%, v/v) were applied at 700 L ha−1, and th...

Efeitos do volume de calda de aplicação e adição de surfatantes organossiliconados na eficiência do MSMA no controle de tiririca

O objetivo desta pesquisa foi avaliar a eficiência do herbicida MSMA no controle da planta daninha tiririca (Cyperus rotundus), quando aplicado com diferentes volumes de calda, associado ou não a surfatantes to tipo organossiliconados. Os tratamentos, dispostos no delineamento de blocos casualizados com quatro repetições, foram: MSMA (2,4 kg ha-1), MSMA (2,4 kg ha¹ + surfatante organossiliconado [marca comercial Silwet L-77] 0,05% v/v) e MSMA (2,4 kg ha-1 + surfatante organossiliconado [marca comercial Break Thru] 0,05% v/v), aplicados em quatro volumes de calda (100, 200, 300 e 400 L ha-1), e duas testemunhas (capinada e sem capina). A pressão de trabalho do pulverizador (3,0 kgf cm-2) foi mantida constante durante as aplicações, para todos os tratamentos. No momento das aplicações as manifestações epígeas de tiririca apresentavam em média oito folhas. O surfatante marca comercial Silwet L-77 mostrou tendência de acelerar a toxidez do MSMA sobre a parte aérea da tiririca; todavia, variações do volume de calda aplicado por hectare com adição ou não de surfatantes organossiliconados não incrementaram o controle dessa planta daninha. O MSMA proporcionou apenas controle regular da tiririca (60-70%).

Gibberellic Acid Application Timing Affects Fruit Quality of Processing Oranges

Gibberellic acid (GA3) increases juice yield of processing oranges, but results are inconsistent. Preliminary research suggested that this variability might be related to application timing. Therefore, we conducted an experiment to determine the optimal time to apply GA3 for increasing juice yield of `Hamlin', `Pineapple', and `Valencia' sweet oranges [Citrus sinensis (L.) Osb.]. Mature trees of each cultivar were sprayed with ≈10 L of a solution of GA3 (45 g·ha-1 a.i.) and organo-silicone surfactant (Silwet, 0.05%) between 2 Sept. and 9 Dec. 1998, and 25 Sept. and 9 Dec. 1999, or remained non-sprayed (control). Generally, the earliest application dates were most effective at maintaining peel puncture resistance above that of control fruit, while the latest application dates resulted in the most green peel color at harvest. Juice yield of `Hamlin' and `Valencia', but not `Pineapple', was increased by GA3 at some application timings and harvest dates in both years. The increase in juice yield was related to time between application and harvest; juice yield of `Hamlin' was greatest ≈2 months, and `Valencia' ≈5 months after GA3 application. Treated fruit often had lower juice Brix than non-sprayed fruit, a phenomenon that often paralleled treatment effects on peel color. When treatments did not increase juice yield but reduced juice Brix, then yield of solids was sometimes lower than for non-treated fruit. Treatments generally delayed flowering of `Pineapple' and `Valencia' but not `Hamlin'.

Foliar-Applied Surfactants and Urea Temporarily Reduce Carbon Assimilation of Grapefruit Leaves

Although urea can be an effective adjuvant to foliar sprays, we examined effects of additional surfactants on urea penetration through leaf cuticles along with the effect of urea with and without surfactants on net gas exchange of leaves of `Marsh' grapefruit (Citrus paradisi Macf.) trees budded to Carrizo citrange (C. sinensis L. Osbeck × Poncirus trifoliata L. Raf.) rootstock. Various combinations of urea, a nonionic surfactant (X-77), and an organosilicone surfactant (L-77), were applied to grapefruit leaves and also to isolated adaxial cuticles. When compared to X-77, L-77 exhibited superior surfactant features with smaller contact angles of droplets deposited on a teflon slide. Both L-77 and X-77 initially increased penetration rate of urea through cuticles, but the effect of X-77 was sustained for a longer period of time. The total amount of urea which penetrated within a 4-day period, however, was similar after addition of either surfactant. Solutions of either urea, urea + L-77, urea + X-77, or L-77 alone decreased net assimilation of CO2 (ACO2) for 4 to 24 hours after spraying onto grapefruit leaves. A solution of X-77 alone had no effect on ACO2 over the 4-day period. Although reductions in ACO2 were similar following sprays of urea formulated with two different surfactants, the underlying mechanisms may not have been the same. For the urea + X-77 treatment, X-77 increased the inhibitory effects of urea on ACO2 indirectly by increasing penetration of urea into leaves. For the urea + L-77 formulation, effects of L-77 on ACO2 were 2-fold, direct by inhibiting ACO2 and indirect by increasing urea penetration. One hour after application, scanning electron microscopy (SEM) of leaf surfaces treated with X-77 revealed that they were heavily coated with the residue of the surfactant, whereas leaves treated with L-77 looked similar to nontreated leaves with no apparent residues on their surfaces. The amount of X-77 residue on the leaves was lower 24 hours after application than after 1 hour as observed by SEM.

Surfactants Increase Toxicity of Glyphosate and 2,4-D to Brazil Pusley

Various combinations of glyphosate and 2,4-D (± surfactant) were evaluated for control of Brazil pusley [Richardia brasiliensis (Moq.) Gomez]. Typical 2,4-D symptoms on plants were manifested within 2 to 3 days after treatment. Application of glyphosate alone had only marginal effects (14%) on Brazil pusley, but the addition of Induce® (nonionic surfactant) significantly increased control to 83% and reduced the fresh weight by 68%. Application of Landmaster®II or a tank-mix of glyphosate + 2,4-D (± surfactants) resulted in 96% to 100% control. Treatment with 2,4-D alone, or with Induce®, or L-77® (organosilicone surfactant) resulted in 84%, 90%, or 100% control, respectively. Very low fresh weights of Brazil pusley were recorded when 2,4-D +Induce® or L-77®, Landmaster®II (± surfactants), or the tank-mix (± surfactants) were applied. In the regrowth studies, shoot weight was greater following application of glyphosate with or without L-77® or Kinetic® (a blend of nonionic and organosilicone) than following other treatments. The fresh weight of the shoots in the regrowth study, recorded following the application of 2,4-D or Landmaster®II (± surfactants), was very low except when Kinetic® was added to Landmaster®II. No regrowth of shoots occurred following the tank-mix treatment. Similar observations were recorded for roots. Plants treated with 2,4-D did not regrow. The presence of 2,4-D in either formulation accelerated synergistic effect of the glyphosate to the target site. Therefore, 2,4-D could be used either as a component of a formulation or in a tank-mix with glyphosate to control Brazil pusley. Chemical names used: N-(phosphonomethyl glycine) (glyphosate); 2,4-dicholorophenoxyacetic acid (2,4-D).

Factors influencing the herbicidal activity of Nep1, a fungal protein that induces the hypersensitive response inCentaurea maculosa

The fungal protein Nep1, produced by Fusarium oxysporum f. sp. erythroxyli in liquid culture, caused extensive necrosis to Centaurea maculosa when water solutions of Nep1 (5 µg ml−1) and an organosilicone surfactant (1,1,1,3,5,5,5-heptamethyltrisiloxanyl propyl-methoxy-poly[ethylene oxide]) were applied as foliar sprays. Nep1 did not cause necrosis when applied with a nonionic surfactant or organosilicone surfactant plus unrefined corn oil. Plant age, protein concentration, organosilicone surfactant concentration, and the presence of a dew period influenced the amount of necrosis caused by Nep1. The addition of an 18-h dew period after treatment resulted in an increase of 10% or more in foliar necrosis at the 0.313 and 1.25 µg ml−1 (0.40 and 1.62 g ai ha−1) Nep1 concentrations. Increasing the spray volume from 129 ml m−2 (1,291.3 L ha−1) to 516 ml m−2 (5,165.2 L ha−1) more than doubled the amount of foliar necrosis caused by the 0.313 µg ml−1 (0.40 g ai ha−1 vs. 1.62 g ai ha−1) Nep1 concentration. A maximum necrosis rating of 95% was reached by 1.25 µg ml−1 Nep1 applied at 516 ml m−2 (6.46 g ai ha−1) followed by an 18-h dew period. Nep1 (6.46 g ai ha−1) remained active when coapplied to Centaurea maculosa with the herbicides 2,4-D or glyphosate (0.13 to 2.58 kg ai ha−1), causing foliar necrosis prior to the herbicides killing Centaurea maculosa. An increase in the organosilicone surfactant concentration from 1 to 2 ml ai L−1 was required to achieve levels of Nep1-induced necrosis on Centaurea maculosa acclimated to direct sun comparable to levels achieved on greenhouse-grown plants. Repeated application of Nep1 (6.48 g ai ha−1) 3 wk after an initial treatment (6.48 g ai ha−1) prevented the recovery of acclimated Centaurea maculosa. Greater damage was caused to acclimated Centaurea maculosa when Nep1 was applied near the middle of the day (80% necrosis at 10:00 A.M. and 85% necrosis at 2:00 P.M.) compared to early or late in the day (25% necrosis at 6:00 A.M. and 10% necrosis at 6:00 P.M.).

The effect of herbicides and surfactants on turf grasses and annual poa

The tolerance of browntop (Agrostis capillaris L) perennial ryegrass (Lolium perenne L) Chewings fescue (Festuca nigrescens Lam) and annual poa (Poa annua L) to twelve herbicides with and without two organosilicone surfactants (Silwet L77 and Silwet S800) were assessed Annual poa was controlled by haloxyfop and clethodim plus S800 Browntop was highly tolerant to chlorsulfuron and metsulfuron and Chewings fescue to haloxyfop fluazifop clethodim and sethoxydim Organosilicone surfactants affected the tolerance of some species to certain herbicides For example Silwet L77 reduced the tolerance of annual poa to glyphosate but S800 increased the tolerance of perennial ryegrass to terbuthylazine The results have implications for the management of cool season turf

579 Thinning Nectarines and Peaches at Flowering with Organosilicone Surfactants

Thinning of nectarines and peaches is largely an expensive manual task. We investigated the use of organosilicone surfactants as thinning materials that can be applied by mechanized sprayers. Of the surfactants tested, Silwet-408 (Witco) and Boost (Dow-Elanco) were the most effective thinning agents. Spray concentrations of 0.1% or 0.25% (v/v) applied at 30% and 60% full bloom, or 0.5% applied at 80% to 90% bloom, reduced by 50% the mass of fruitlets that had to be hand-thinned and increased the average weight of harvested fruit by up to 20%. When 0.75% to 1% surfactants were applied at 80% to 100% full bloom, fruit yield was reduced by up to 90%. The sprays did not affect fruitlets that had set already, nor did they cause damage to leaves or young shoots. Open flowers were more susceptible to the surfactants than were flowers at tight-bloom or balloon stage. Ion leakage from both petals and flower bases increased in proportion to concentration of surfactant applied, but there was no increase in lipid peroxidation.

187 Foliar Application of Urea to Citrus: Effects of Non-ionic and Organosilicone Adjuvants

Urea solutions, with or without non-ionic (X-77) and organosilicone (L-77) surfactant, were applied to Citrus leaves and isolated cuticles to examine adjuvant effects on urea uptake and leaf net gas exchange. When compared to X-77, L-77 exhibited superior features as a surfactant, resulting in smaller contact angles of droplets deposited on teflon slide. Both L-77 and X-77 had a strong effect on penetration rate of urea within first 20 min of experiment. Effect of L-77 on urea penetration rate decreased quickly within next 20 min, whereas the effect of X-77 was sustained over a 24-h period following application. When compared to solution of urea alone, addition of X-77 to urea resulted in significant increase of the total amount of urea that penetrated the cuticles. The effect of L-77 was smaller, although the total amount of urea that penetrated the cuticles within a 4-day period was similar for both surfactants. Solutions of either urea alone, urea+L-77 and urea+X-77, or L-77 alone, induced a negative effect on net CO2 assimilation (ACO2) for 4 to 24 h after they were sprayed onto leaves. X-77, when applied alone, had no effect on ACO2. Scanning electron microscopy revealed that 1 h after application, leaf surfaces treated with X-77 appeared to be heavily coated, as opposed to those treated with L-77, which appeared similar to untreated control leaves.

Effects of some agricultural tank-mix adjuvants on the deposition efficiency of aqueous sprays on foliage

The effects of 10 commercially available tank-mix adjuvants on the retention and coverage of aqueous sprays on foliage were examined quantitatively under track sprayer conditions, following application at their maximum recommended rates. Substantial enhancement of fluorescein retention was observed only on water-repellent barley and peas, but the differences in performance between the additives were considerable. Addition of the water-soluble tallow amine and nonylphenol surfactants gave the largest increases in retention, whereas there was little improvement in efficiency compared with water alone after inclusion of either the latex- or pinolene-based products or ammonium sulphate. Retention enhancement was also achieved using the mineral oil, vegetable oil, methylated vegetable oil and phospholipid ECs and the organosilicone surfactant, but this was often much less than that obtained for the water-soluble surfactants; the best EC was the methylated vegetable oil which also had the highest emulsifier content. Although spray quality was altered significantly in the presence of many of the adjuvants, modifications to this parameter alone could not account for changes observed in deposition efficiency, because retention enhancement was recorded in sprays with volume median diameters both smaller and larger than water. There was a better correlation between retention efficiency and the dynamic surface tension of the corresponding spray liquids, with the exception of the organosilicone, which, as expected from its high surface activity, gave essentially complete spray coverage on leaves. Nevertheless, good coverage could still be achieved by adding the two water-soluble surfactants, as well as the methylated vegetable oil and phospholipid ECs. Coverage performance of the other adjuvants tested was poor in comparison, reflecting, in part, their inferior retention enhancing properties.

Influence of Adjuvants on Itchgrass (Rottboellia cochinchinensis) Control in Corn (Zea mays) with Nicosulfuron and Primisulfuron1

In field experiments, nicosulfuron at 35 g ai/ha controlled itchgrass in corn 28 d after treatment better than primisulfuron at 39 g ai/ha (80 vs. 44%). Control with both herbicides was greater when applied to six-leaf itchgrass than to 10-leaf and with the addition of nonionic surfactant than with an organosilicone surfactant and methylated seed oil blend. Weed control for nicosulfuron plus nonionic surfactant resulted in corn yield approximately 1.5 times that of primisulfuron plus nonionic surfactant and 1.6 times that of nicosulfuron plus an organosilicone surfactant and methylated seed oil blend. When primisulfuron was applied with organosilicone surfactant and methylated seed oil rather than nonionic surfactant, corn yield was reduced by 25%. For nicosulfuron with nonionic surfactant, corn yield averaged approximately twice that of the nontreated check. In other field experiments, itchgrass control 28 d after treatment with nicosulfuron was enhanced with addition of an organosilicone and nonionic surfactant blend or methylated seed oil (83 and 78%, respectively) compared with nonionic surfactant (69%). Nicosulfuron was less effective when applied with crop oil concentrate or organosilicone surfactants compared with nonionic surfactant.Nomenclature: Nicosulfuron, 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide; primisulfuron, 2-[[[[[4,6-bis(difluoromethoxy)-2-pyrimidinyl]amino]carbonyl]amino]sulfonyl]benzoic acid; itchgrass, Rottboellia cochinchinensis (Lour.) W. Clayton #3 ROOEX; corn, Zea mays L. ‘DeKalb 689’.Additional index words: Crop oil concentrate, methylated seed oil, nonionic surfactant, organosilicone surfactant, ROOEX.Abbreviations: DAT, days after treatment; POST, postemergence; PRE, preemergence.

Influence of Adjuvants and Bromoxynil on Absorption of Clethodim

The effect of nonionic surfactant, crop oil concentrate, organosilicone surfactant, methylated seed oil, and a blend of organosilicone surfactant and methylated seed oil on absorption of14C-clethodim was evaluated in barnyardgrass (Echinochloa crus-galli). Absorption of14C-label was greatest during the first 40 min after application when14C-clethodim was applied with methylated seed oil or a blend of methylated seed oil and organosilicone surfactant. These adjuvants increased the rate of absorption more than crop oil concentrate, organosilicone surfactant, or nonionic surfactant. Crop oil concentrate was more effective than organosilicone or nonionic surfactant in increasing absorption, with nonionic surfactant being more effective than organosilicone surfactant. These results generally agreed with the order of increasing efficacy of clethodim on barnyardgrass as affected by adjuvants in field experiments. Another study was conducted to determine the effect of bromoxynil on absorption and translocation of14C-clethodim in yellow foxtail (Setaria glauca). Bromoxynil reduced absorption of14C–clethodim 4, 8, and 24 h after application and also reduced the amount of14C-label translocated from the treated leaf. These data suggest that antagonism of clethodim control of yellow foxtail by bromoxynil observed in previous research can be attributed partially to decreased absorption and translocation of clethodim.

221 Gibberellic Acid Application Timing Effects on Juice Yield and Peel Quality of `Hamlin' Oranges

Gibberellic acid (GA) applied in late summer or fall delays subsequent loss of peel puncture resistance (PPR) and development of yellow peel color in many citrus cultivars. Our objective was to determine the optimal time to apply GA for increasing juice yield of `Hamlin' sweet orange [Citrus sinensis (L.) Osb.]. Mature trees on sour orange (Citrus aurantium L.) rootstock were sprayed with ≈24 L of a solution of GA (45 g a.i./ha) and organo-silicone surfactant (Silwet, 0.05%). Trees were sprayed on 26 Aug., 9 Sept., 2 Oct. (colorbreak), or 13 Oct. 1997, or nonsprayed (control). Peel puncture resistance, peel color, and juice yield were evaluated monthly between Dec. 1997 and Mar. 1998. Fruit from trees sprayed with GA had peels with higher PPR and less yellow color than fruit of control trees for most of the harvest season. The effect of GA on PPR and peel color lasted about 5 months. Juice yield was usually numerically greater for GA-treated fruit than for nontreated fruit. Fruit treated with GA at color break had significantly greater juice yield when harvested in late February than fruit from control trees. Thus, GA applied at color break appears to be the most effective time for enhancing peel quality and juice yield of `Hamlin' oranges.