Second year weed control - in May or June. Later applications are less effective. Application tips Knockdown herbicides work best on healthy weeds, especially after rain has stimulated their growth. They are less effective on unhealthy weeds, especially if nitrogen deficient. Dense weeds must be removed by heavy grazing, cultivation or knockdown herbicide before applying residual herbicides.
Residual herbicides work best if applied to moist soil.
Only a residual herbicide is needed if the pre-planting application is done after soil preparation, but before weed emergence. After residual herbicides are applied, allow 50 mm of rain and at least two weeks before planting eucalypts, or 25 mm of rain and at least one week before planting pines. On other soils they are more likely to damage the trees, so reduce application rates accordingly. For example, sulfometuron methyl is safe at low pH because it is adsorbed by clay particles in the soil, but at high pH the same application rate may damage trees because the chemical is more mobile. In high rainfall areas, residual chemicals are effective for one to three months depending on soil conditions.