The influence of growth stage and application site on movement and effect of glyphosate in Cirsium arvense (L.) Scop. : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Plant Science at Massey University
Glyphosate was applied at different rates to the upper parts of Cirsium arvense plants at various growth stages in a glasshouse experiment. Measurements and observations were made of the plants over a period of several months following treatment. In other experiments, glyphosate was applied to different parts of plants and to either side of leaves to determine the importance of herbicide placement on its subsequent effectiveness. Complete death of plants, as signified by decomposition of the roots, generally occurred only where the maximum dose (100 mg ai/plant) was applied, and occurred consistently only for those plants treated at the post-flowering growth stage. However, plants treated on the lower parts of stems died in some cases after application of 25 mg. The symptoms and damage resulting from glyphosate action are described and discussed. Extensive translocation of glyphosate appeared to occur, both symplastically and apoplastically, with greater translocation to the roots and untreated daughter stems occurring from treated tissue situated low on the stem. Stem tissue seemed as efficient at absorbing glyphosate as leaves, and likewise no difference in absorption rates by upper compared with lower leaf surfaces was detected. Complete control of plants occurred only if all stems simultaneously wilted approximately 1 month after treatment, apparently due to disruption of the roots. Plants varied considerably in response to treatment and no relationship could be established between degree of effect and plant size, plant sex or relative humidity at the time of treatment. The results are discussed in relation to ropewick application of glyphosate to C. arvense plants.