Effect of split applications of herbicides on the control of Hypericum perforatum L. (St. John's wort) and regeneration of native grasses and annual clovers on non-arable land

M.H. Campbell and H.I. Nicol, NSW Agriculture, Orange Agricultural Institute, Orange, New South Wales 2800, Australia.


Summary

The effects of single and split applications of herbicides on the kill of Hypericum perforatum L.(St. John's wort) and the regeneration of annual clovers and native perennial grasses were recorded from 1997 to 1999 in an experiment near Wellington, New South Wales. Split applications of fluoroxypyr (0.4 + 0.6, 0.6 + 0.4 and 0.6 + 0.6 kg a.i. ha-1) and triclopyr + picloram ((0.9 + 0.3) + (0.9 + 0.3) kg a.i. ha-1) at flowering in Novembers 1997 and 1998 gave 100% kill of the weed while split applications of glyphosate at 1.35 + 1.35 kg a.i. ha-1 were less successful. Split applications of all three herbicides in November 1997 and February 1998 were less effective in killing H. perforatum than applications in Novembers 1997 and 1998, probably because the weed had insufficient time to recover from the November 1997 spraying and grow sufficient foliage to absorb the herbicide from the February 1998 application. Single applications of all herbicides resulted in <100% kill of the weed, the small populations remaining after spraying having the potential to increase to large infestations over time.

Single and split applications of fluoroxypyr had no deleterious effects on the regeneration of annual clovers with and without superphosphate and promoted the ground cover and quality of native perennial grasses. Triclopyr + picloram reduced the ground cover of clovers and glyphosate reduced the ground cover of native perennial grasses. The results suggest that long term control of H. perforatum could be achieved using split applications of fluoroxypyr and aerial distribution of superphosphate and Trifolium subterraneum seed, followed by heavy stocking in winter/early spring to graze any H. perforatum present, with animal free periods in summer to promote native grass dominance.

 

Plant Protection Quarterly (2000) 15 (3) 119-122.