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Vladimir Orbovic, John L. Jifon, and James P. Syvertsen

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.

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Vladimir Orbović, Diann Achor, and James P. Syvertsen

; Schreiber and Schönherr, 1990 ). Thus, the dynamics of cuticular penetration can yield insights into foliar uptake ( Orbović et al., 2001a ) or uptake into the fruit tissue. The organosilicone surfactant, L-77, has a high surface activity, which results in

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Nikolaos Koutinas, Thomas Sotiropoulos, Antonios Petridis, Dimitrios Almaliotis, Emmanuil Deligeorgis, Ioannis Therios, and Nikolaos Voulgarakis

from treated leaves to the fruit ( Swietlik and Faust, 1984 ). B mobility in kiwifruit is also considered low ( Brown and Hu, 1998 ). Schonherr (2001) studying the cuticular penetration using Ca salts found that the rates of penetration were greatly

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Yang Gao and Deying Li

.E. Purcell, L.C. 2001 Quantifying turfgrass cover using digital image analysis Crop Sci. 41 1884 1888 Schonherr, J. Fernandez, V. Schreiber, L. 2005 Rates of cuticular penetration of chelated Fe-III: Role of humidity, concentration, adjuvants, temperature

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Martin M. Williams II, Loyd M. Wax, Jerald K. Pataky, and Michael D. Meyer

poor cuticular penetration and/or translocation of the herbicide. Most evaluations of sweet corn tolerance to nicosulfuron have resulted in a continuous range of responses ( Morton and Harvey, 1992 ; O'Sullivan and Bouw, 1998 ; Robinson et al., 1993

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Kathryn M. Santos, Paul R. Fisher, and William R. Argo

.A. 2005 Systemic signaling in wound response Curr. Opin. Plant Biol. 8 369 377 Schonherr, J. 2001 Cuticular penetration of calcium salts: Effects of humidity, anions and adjuvants J. Plant Nutr. Soil Sci. 164 224

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Jialin Yu and Nathan S. Boyd

, and mesosulfuron than ‘Florida Fantasy’. We speculate that the variable tolerance of caladium cultivars to the SU herbicides is due to differential cuticular penetration, herbicide translocation, or metabolism. In previous research, Burton et al

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Holger Weichert, Stefanie Peschel, Moritz Knoche, and Dieter Neumann

. Schreiber, L. 2005 Rates of cuticular penetration of chelated Fe III : Role of humidity, concentration, adjuvants, temperature, and type of chelate J. Agr. Food Chem. 53 4484 4492 Weichert, H. Knoche, M. 2006a

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Matthew Arrington, Mateus S. Pasa, and Todd C. Einhorn

. Petracek, P.D. 2014 Effects of pH, humidity, and rewetting on cuticular penetration of ABA Acta Hort. 1042 143 150 Ngugi, H.K. Schupp, J.R. 2009 Evaluation of the risk of spreading fire blight in apple orchards with a mechanical string blossom thinner