EFFECT OF TIME OF APPLICATION OF HERBICIDES ON THE LONG-TERM CONTROL OF ST-JOHNS WORT (HYPERICUM-PERFORATUM VAR ANGUSTIFOLIUM)

The effect of application time of herbicides on the long-term control of St. John''s wort was investigated at Tuena, New South Wales [Australia]. The herbicides used were: 2,4-D, 2,4,5,-T, 2,4-D + 2,4,5-T, picloram + 2,4-D and glyphosate. Each of these was applied in Feb., May, Aug. and Nov., 1976, and regrowth of wort was monitored until Feb. 1978. The percentage ground cover of unsprayed St. John''s wort varied between 75% and 85% over the experimental period. Initially all herbicides reduced the ground cover of St. John''s wort from > 75% to < 15%. Thereafter, the regrowth of wort depended on the long-term effect of the herbicides. At the final assessment in Feb. 1978, the most effective herbicide treatments were: from the Feb. and May applications, glyphosate and picloram + 2,4-D; from the Aug. application, picloram + 2,4-D; and from the Nov. application, picloram + 2,4-D, 2,4-D + 2,4,5-T and 2,4-D.