The herbicidal effect of glyphosate applied to gorse (Ulex europaeus L.) was improved by the addition of increasing amounts (0.5-20 g/litre) of Silwet L-77, an organosilicone surfactant. Increasing the rate of herbicide also enhanced control. There was a highly significant interaction between surfactant rate and herbicide dosage; as the amount of Silwet L-77 was increased the rate of glyphosate could be reduced without loss of herbicide efficacy. However, without any added organosilicone surfactant, glyphosate did not provide more than 73% control of gorse at any rate up to 6.5 kg a.i./ha. With the addition of Silwet L-77, complete mortality of all plants could be achieved with 2.2 kg glyphosate/ ha. Neumann P M. Prinz R. 1974. Evaluation of surfactants for use in the spray treatment of iron chlorosis in citrus trees. Journal of Science. Food arid Agriciiltiire 25:221-226. Policello G A, Murphy G J. 1992. Influence of cosurfactants on spreading ability of organosilicone wetting agents. In Third Ititernutiotial Symposium on Adjiiuants f o r Agrochemicals (Abstract). UK: SCI Pesticides Group. Stevens P J G, Gaskin R E, Hong S 0. Zabkiewicz J A. 1991. Contributions of stomata1 infiltration and cuticular penetration to enhancements of foliar uptake by surfactants. Pesticide Science 33:371-3x2. Turner D J. 1985. Effects on glyphosate performance of formulation, additives and mixing with other herbicides. In The Herbicide Glvphosate. pp. 221-240. London: Butterworths. Wyrill J B, Burnside 0 C. 1977. Glyphosate toxicity to common milkweed and hemp dogbane as influenced by surfactants. Weed Science 25:275-287. Zabkiewicz J A, Gaskin R E. 1989. Effect of adjuvants on uptake and translocation of glyphosate in gorse (Ulex eiiropaeus L.). In Adjiiaants and Agrochetnicmls. Volirtne I ; Mode of Action arid Physiological Acriuity. pp. 111-150. Boca Raton: CRC Press. Zabkiewicz J A, Coupland D, Ede F. 1988. Effects of surfactants on droplet spreading and drying rates in relation to foliar uptake. In Pesticide Formulations, Innovations and Deuelopments, A C S S~tnposiutn Series 371. pp. 77-89. Washington DC: American Chemical Society. Zabkiewicz J A, Gaskin R E, Balneaves J M. 1985. Effect of additives on foliar wetting and uptake of glyphosate into gorse. Application and Biology. British Crop Protection Coiincil Monograph 28:127--133.
Researchers in New Zealand, Scotland, South Africa, Texas, and Alabama provided data on growth responses owing to nursery management practices and weed control after outplanting. Nursery treatments included nitrogen fertilization (0 vs. 168 kg/ha), seedling grades (small-diameter vs. large-diameter seedlings), and a comparison of stock types. Weed-control treatments varied by study and included broadcast and spot applications. Interactions between nursery practices and weed control were examined. Regardless of location, growth (2–8 years after planting) was increased as seedling diameter increased. Practices that increase average seedling diameter in the nursery are typically less costly than silvicultural practices required to obtain similar growth responses from small-diameter stock. Although interactions were observed among sites, stock size, and intensity of weed control, large-diameter stock consistently grew better than small-diameter stock regardless of site or site-preparation method. Thus, increasing the investment of regeneration expenditures at the nursery, relative to that put into site preparation, will substantially improve financial returns on investment. Further research needs in this area are also discussed.
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