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.
Residual herbicides pose a risk to the environment if applied to waterlogged soils.
Residual herbicides don't work well on cloddy soils because the chemical is poorly distributed. Plough before mounding to break up the clods. If applied to freshly cultivated soil, they may leach rapidly and be less effective. Many mound ploughs used to prepare sites for tree planting are fitted with a roller to help consolidate the mounds. Flattened mounds are also easier to walk along when planting.