Moritz Knoche

Effect of droplet size and carrier volume on performance of foliage-applied herbicides

Abstract Frequently, spray application of agrochemicals is effective but inefficient. A better understanding of the effects of spray application factors on spray performance may contribute to increased efficacy. In this paper the effects of droplet size and carrier volume on performance of foliage-applied herbicides are reviewed. Generally, performance increased as droplet size decreased at constant carrier volume, irrespective of the droplet size range investigated. Performance of systemic herbicides increased more consistently with decreasing droplet size, compared with herbicides with a contact mode of action. For monocotyledons with a predominantly vertical structure, decreasing droplet size in the size class 150 μm, or compared with dicotyledons with a predominantly horizontal structure. Further, decreasing droplet size more frequently enhanced herbicide performance on difficult-to-wet (contact angle of water droplets >110 degrees) than on easy-to-wet plants (contact angle −1 ), performance more frequently decreased as carrier volume decreased, whereas the reverse trend was observed at high carrier volumes (>400 l ha −1 ). A significant interaction between the effect of carrier volume and herbicide type was observed. For glyphosate, plant response consistently increased as carrier volume decreased, but for other herbicides performance generally decreased as carrier volume decreased. There was no difference in carrier volume effects between herbicides with a systemic or a contact mode of action, or between response of monocotyledonous or dicotyledonous species. However, on difficult-to-wet plants, decreasing carrier volume more frequently increased herbicide performance compared with easy-to-wet plants. The effects of the spray application factors droplet size and carrier volume on individual stages of the composite spray application process (i.e. canopy penetration and droplet impaction, retention, foliar uptake and the induction of a biological response) are discussed.

Studies on water transport through the sweet cherry fruit surface: II. Conductance of the cuticle in relation to fruit development

Abstract. Water conductance of the cuticular membrane (CM) of sweet cherry (Prunus avium L. cv. Sam) fruit during stagesxa0II and III (31–78xa0days after full bloom, DAFB) was investigated by gravimetrically monitoring water loss through segments of the exocarp. Segments were mounted in stainless-steel diffusion cells, filled with 0.5xa0ml of deionized water and incubated for 8xa0h at 25±2xa0°C over dry silica. Conductance was calculated by dividing the amount of water transpired per unit surface area and time by the difference in water vapor concentration across the segment (23.07xa0g m–3 at 25xa0°C). Fruit mass and fruit surface area increased 4.9- and 2.8-fold between 31 and 78xa0DAFB, respectively. However, CM mass per unit area decreased from 3.9 to 1.5xa0g m–2, and percentage of total wax content remained constant at about 31%. Stomatal density decreased from 0.8 to 0.2xa0mm–2 (31–78xa0DAFB). Total conductance of the CM on the fruit cheek (gtot.) remained constant during stagexa0II of development (approx. 1.38×10–4xa0m s–1 from 31 to 37 DAFB), increased to 1.73×10–4xa0m s–1 during early stagexa0III of fruit growth (43–64 DAFB) then decreased to 0.95×10–4xa0m s–1 at maturity (78xa0DAFB). Partitioning gtot. into cuticular (gcut.) and stomatal conductance (gsto.) revealed that the relative contribution of gcut. to gtot. increased linearly from 30% to 87% of gtot. between 31 and 78xa0DAFB, respectively. On a whole-fruit basis, gtot. and gcut. consistently increased up to 64xa0DAFB, and decreased thereafter. A significant negative linear relationship was obtained between gcut. and CM thickness, but not between the permeability coefficient (p) and CM thickness. Further, p was positively related to strain rate, suggesting that strain associated with expansion of the fruit surface increased p.

Finite dose diffusion studies: I. Characterizing cuticular penetration in a model system using NAA and isolated tomato fruit cuticles†

A finite dose diffusion system was employed to study cuticular penetration of 2-(1-naphthyl) [1−14C]acetic acid (NAA) from simulated spray droplets through enzymatically isolated tomato fruit cuticles (Lycopersicon esculentum Mill cv Pik Red). Isolated cuticles were mounted on diffusion half-cells with the cell wall surfaces facing a 20u2009mM citric acid receiver solution (pH 3.2, volume 2.9u2009ml, prepared with deionized water). A 5-µl donor droplet containing NAA at 100u2009µM in 20u2009mM citric acid buffer (pH 3.2) was applied to the outer surface. Penetration was monitored by repeated sampling of the receiver solution. NAA penetration was characterized by (1) an initial lag phase of about 2.3u2009h, (2) a phase of nearly constant maximum rate of penetration averaging 6.3% of applied NAA h−1 (equivalent to 0.032u2009nmol h−1) and (3) a plateau phase approaching an asymptote at 81.2% of applied NAA (equivalent to 0.406u2009nmol) at 120u2009h. Within 1u2009h after application droplets appeared dry on visual inspection. Immediately after droplet drying, 7.0% of the applied NAA was sorbed to the cuticle, but only 0.5% penetrated into the receiver solution, indicating that penetration occurred almost exclusively from the apparently dry deposit. At 120u2009h, 5.2% of the NAA applied was associated with the deposit and 4.3% with the cuticle. The distribution of maximum rates of penetration was log-normal, but penetration at 120u2009h followed a normal distribution. Cuticle thickness (estimated 5–25u2009µm) had no significant effect on NAA penetration. Maximum rates of penetration through pepper fruit and citrus and ficus leaf cuticles were 4.9-, 2.6- and 0.1-times that through tomato fruit cuticles. At 120u2009h, penetration averaged 85.5, 79.5 and 34.7% for pepper, citrus and ficus cuticles, respectively. Extracting epicuticular and embedded waxes increased NAA penetration rates through tomato fruit cuticle more than three-fold, but had little effect on penetration at 120u2009h (71.0 vs 87.7% for cuticular vs dewaxed cuticular membranes). The maximum penetration rate and total penetration were found to be useful parameters in describing the penetration time-course. n n n n© 2000 Society of Chemical Industry

Factors affecting the absorption of gibberellin A3 by sour cherry leaves

Abstract The effects of leaf surface, light, temperature, time, concentration, and pH on absorption of [14C]gibberellin A3 (GA3) into newly expanded sour cherry (Prunus cerasus L., cv. Montmorency) leaves were investigated. GA3 penetration was sevenfold greater into the abaxial (7.8%) than adaxial (1.1%) surface. Light markedly enhanced penetration into the abaxial but not the adaxial surface. Penetration was greater at 25°C than at 15° or 35°C. GA3 absorption by the adaxial surface was rapid initially (0–1 h), followed by a slower, almost constant rate of uptake after the droplets dried (1–24 h). Rate of GA3 uptake by the abaxial surface approached zero after 3h. Uptake by the tissue fraction of the adaxial surface was linearly related ( r 2 = 0.99 ∗∗ ) with GA3 concentration from 0.05 to 5 m m , whereas uptake by the abaxial surface was saturated between 1 and 5 m m GA3. Decreasing pH from 5.0 to 3.0 resulted in increased GA3 uptake.

Studies on octylphenoxy surfactants: IX. Effect of oxyethylene chain length on GA3 absorption by sour cherry leaves

The effect of a homologous series of octylphenoxy surfactants, α-[4-(1,1,3,3-tetramethylbutyl)phenyl]-ω-hydroxypoly-(oxy-1,2-ethanediyl), condensed with 5, 7–8, 9–10, 16, and 30 oxyethylene (EO) units on enhancement of gibberellic acid (GA3) absorption by leaves ofPrunus cerasus cv. Montmorency was studied. Increasing EO chain length (5–30 EO) increased surface tension (27.5–35.3 mN m−1) and contact angles on adaxial (21–36°) and abaxial (28–49°) leaf surfaces. With increasing EO content, the form of GA3 deposits from droplets on the leaf surface changed from an annulus shape (5 and 7–8 EO) to globular forms covering increasingly smaller interface areas (9–10 to 30 EO). The surfactants increased GA3 uptake, the magnitude decreased with an increase in oxyethylene chain length. Similar trends were found for both the adaxial and abaxial surfaces. Penetration through the abaxial surface was linearly related to the logarithm of the oxyethylene content of the surfactant molecule (r2=0.934**) and to the hydrophilic: lipophilic balance (r2=0.926**). Absorption by the abaxial surface was approximately one order of magnitude greater than by the adaxial surface.

Droplet sizing using silicone oils

Abstract The ISO standard protocol for determining size of droplets suspended between two layers of silicone oils of differing viscosity was evaluated in experiments using a monosize droplet generator. Cross-sectional areas of 0.27-nl droplets captured in silicone oils decreased linearly with time until droplets disappeared at 26xa0min after application. Rates of decrease in cross-sectional area of droplets were independent of droplet size (range 0.27–269xa0nl), but decreased as the gradient in water vapour concentration between droplet and ambient atmosphere decreased. Saturating silicone oils with water reduced rates of decrease in cross-sectional areas of droplets (−37%). Diffusion studies established that the amount of water diffusing through silicone oil increased linearly with time. Permeance to water vapour was inversely related to thickness of the oil layer. Permeability coefficients averaged 45.8×10 −9 and 29.5×10 −9 xa0m 2 xa0s −1 for low- (9.6xa0cSt) and high-viscosity (10xa0350xa0cSt) silicone oil and were up to 52-fold higher than for mineral oils of comparable viscosity. Our data suggest that the high water vapour permeability of silicone oil and the solubility of water in silicone oil accounted for the decrease in size of droplets captured in silicone oil. Based on our findings, the ISO standard protocol should be modified to correct for these effects.

Finite dose diffusion studies: II. Effect of concentration and pH on NAA penetration through isolated tomato fruit cuticles

The effects of NAA [2-(1-naphthyl)acetic acid] concentration and pH on penetration of NAA from aqueous droplets (5 μl) through isolated tomato (Lycopersicon esculentum) fruit cuticles were studied using a finite dose diffusion system. Penetration time-courses were characterized by a lag phase, which generally extended beyond the time of droplet drying. Initially penetration rates increased, reached a maximum penetration rate, remained constant for several hours, and then decreased with time. Penetration approached a plateau within 120h after droplet application. Increasing NAA concentration in the donor droplet increased NAA penetration in both the presence and absence of the citric acid buffer (20mM, pH 3.2). Maximum rates of penetration and the total amount of NAA that penetrated at 120 h were both linearly related to the initial concentration of the donor droplet (ranging from 0.001 to 0.1 mM NAA). The apparent first-order rate constants for the concentration dependence of NAA penetration rates were greater with buffer than without (0.94 x 10 -8 vs 0.50 × 10 -8 ms -1 , respectively). While pH of the receiver solution (pH 6.2 vs 2.2) did not affect penetration, decreasing donor pH from 6.2 to 2.2 increased NAA penetration at 120h.