Studies in the Foliar Uptake and Translocation of Pesticides

Cook, Gordon T (1979) Studies in the Foliar Uptake and Translocation of Pesticides. PhD thesis, University of Glasgow.

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This thesis is principally an investigation of the factors affecting the foliar uptake and translocation of pesticides with particular emphasis on the influence of additives on the herbicide aminotriazole. The work was subdivided as follows 1. A discussion of the various classes of additives which may influence foliar penetration and/or translocation with reference to their mode of action. 2. An investigation of the influence of adjuvants and humidity on the uptake of aminotriazole. The findings can be summarised as follows Penetration of bean leaves (Phaseolus vulgaris var. Canadian Wonder) was greatly enhanced under high humidity conditions (10% penetration in 17h at the low humidity level (LHL) compared with 100% at the high humidity level (HHL) ). The addition of polyoxyethylene 20 sorbitan monolaurate (polysorbate 20) to the spray fluid increased penetration on all occasions at the LHL. The increase obtained was found to be dependent on the concentration of polysorbate 20. Indeed, the w/w ratio of aminotriazole/polysorbate 20 seemed to be of primary importance. A 1/2 ratio appeared to bring about optimum penetration. The polysorbate 20 itself was not found to be taken up by the leaf to any great extent (5.4% penetration in 5h compared with 77.4% of the aminotriazole). The inclusion of polysorbate 20 at the HHL resulted in an increase in aminotriazole penetration at low polysorbate 20 concentrations (0.2-12.8g/litre) and a non-significant decrease over the aqueous control at a concentration of 40g/litre. Although aminotriazole penetration in the presence of polysorbate 20 (6.4g/litre) was increased at the HHL compared with the LHL, polysorbate 20 penetration was reduced. The addition of glycerol to the spray solution increased aminotriazole penetration on all occasions at the LHL while at the HHL none of the concentrations tested enhanced penetration. A polysorbate 20 plus glycerol combination (6.4g + 0.6ml/litre) gave the same order of penetration (98. 4 and 94. 0%) at the HHL and LHL respectively. In both cases, penetration exceeded that obtained with the corresponding polysorbate 20 and glycerol controls. 3. An investigation of the uptake by bean leaves (P. vulgaris var. Canadian Wonder) of aminotriazole from humectant-surfactant combinations and the influence of humidity on their effects. The findings can be summarised as follows Aminotriazole penetration was not greatly influenced by the addition to the spray solution of dimethyformamide (DMF), dimethyl sulphoxide (DMSO), ethylene glycol and polypropylene glycol 400 (PPG 400). However, the addition of polysorbate 20 (0.2 - 1.0g/litre) to spray solutions of the above additives and glycerol (5. 0ml/litre, except for DMF, 50.0ml/litre) substantially increased uptake to 80-100% in all cases at 50+10% relative humidity (r.h.). Similar trends were found when a range of polysorbate surfactants (0.2g/litre) were applied to solutions containing either DMSO or glycerol (5.0ml/litre). Humidity was found to have a critical effect upon such humectant-surfactant combinations. With DMSO-polysorbate 20 the following uptake figures were recorded: <30% r.h. - 3.1%; 45+/-10% r.h. - 86.8%; 55-65% r.h. - 48.2% and 100% r.h. - 0.3%. Similar trends were recorded with other combinations. Further studies revealed that the adverse effect of humidity on DMSO-polysorbate 20 mixtures could be at least partially overcome by regulating the DMSO concentration. 4. An investigation of the mode of action of thiocyanate and iodide in aminotriazole formulations. The findings are summarised as follows Ammonium thiocyanate (NH4SCN) was shown to inhibit aminotriazole oxidation in two free radical generating systems, namely (a) riboflavin photo sensitised oxidation, (b) oxidation by hydroxyl radicals. Evidence from in vitro studies is presented to show that NH4SCN could enhance aminotriazole performance by being preferentially oxidised within the leaf, thereby preventing aminotriazole free radical formation and subsequent conjugation with amino acids and other plant constituents. This opens up the possibility of a whole new range of additives which could enhance translocation by inhibiting free radical reactions. A comparison of possible inhibitors revealed that iodide and perhaps bromide and cyanide could be of use in this respect, Asulam was also found to be oxidised by the two free radical generating systems mentioned above. Again, the degree of oxidation was decreased by thiocyanate, iodide and also by ferrocyanide. This would suggest that additives such as NH4SCN may be of wider use than is at present recognised. In addition to inhibiting free radical reactions, NH4SCN, KSCN, NaSCN, Nal and KI were shown to have a considerable effect on aminotriazole uptake by bean leaves (P. vulgaris var. Canadian Wonder). Mgl2, Cal2 and Ca(SCN)2 had little effect on uptake. (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry, Agriculture
Date of Award: 1979
Depositing User: Enlighten Team
Unique ID: glathesis:1979-78799
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 14:53
Last Modified: 30 Jan 2020 14:53

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