Improving herbicide effectiveness on Hypericum perforatum L. (St. John's wort) and replacing it with pastures sown on non-arable land
M.H. Campbell and H.I. Nicol, NSW Agriculture and Co-operative Research Centre for Weed Management Systems, Forest Road, Orange, New South Wales 2800, Australia.
Experiments at Orange and Gallymont, New South Wales, examined the effects on Hypericum perforatum (St. John's wort) of: rate and type of herbicide; time of spraying; overspraying at annual intervals; rate of water carrier; and spraying and oversowing of improved pasture species. The only herbicide treatment that completely killed H. perforatum was two applications of fluoroxypyr at annual intervals; 0.4 kg a.i. ha-1 in summer 1993 followed by 0.6 kg a.i. ha-1 in summer 1994. Other herbicides that substantially reduced the ground cover of H. perforatum were triclopyr + picloram, glyphosate, and glyphosate + metsulfuron. Fluoroxypyr had no effect on the regeneration of annual legumes and did not damage grasses, whereas triclopyr + picloram killed legumes and glyphosate killed grasses. Monthly application of three herbicides between October and February yielded different results at two different locations and the effect of rate of water carrier had little effect on herbicide efficiency. Spraying H. perforatum and sowing improved species appeared to be the best treatment for long-term control of the weed because improved pasture species established and replaced the weed.
Plant Protection Quarterly (1997) 12 (2) 93-96.