Tillers should be set between 1-2 inches for plantations without woody weeds. Trees send out surface roots which are the primary receptors of rainfall and initial fertilizer applications. Minimize damage to these roots by keeping tillers shallow. On forest sites with woody perennial weeds, tillers will have to be set lower to sever the roots of woody intruders. Chemical weed control is favored oftenbecause it kills the weed in one step, whereas, mechanical weed control requires continuous maintenance.
Some herbicides are selective and can be applied over trees to kill the targeted weed species.
Non selective herbicides can be fatal when applied to above ground parts of the tree. Absorption of these toxic chemicals through the root system is very slight to none for labeled forestry herbicides. Chemical control is very effective but should be applied carefully. Roots need oxygen to grow. Flooding conditions 'choke' off roots while drought conditions dry out roots.