Manufactured by the Monsanto Corporation, Roundup is a glyphosate-based herbicide used by home gardeners to kill problematic weeds in the garden and surrounding landscape. One of the difficulties of using Roundup around trees is that the herbicide, if it gets on the tree or root, can damage the tree and even kill it. But with the proper pressure settings, careful application and safety precautions, you should be able to spray Roundup around trees and their roots.
Put on safety goggles and protective gloves. For extra skin protection, wear a long-sleeved shirt and long pants.
Turn the Roundup bottle's nozzle to a medium to low spray strength. If you're using a pump and spray product, make sure that the spraying device is turned to a low-pressure strength.
Spray the Roundup carefully so that none of the herbicide gets onto the tree or roots. Aim the bottle directly at the weeds that you want to kill, and only use the product when there is no wind, which could blow the spray onto your trees.
Cut off small suckers from trees that produce them, such as a variety of shrubs and fruit trees like pear, plum and peach. If you accidentally spray the suckers with the Roundup, then immediately cut off the sucker, to prevent damage to the whole tree.
Keep people and pets away from the treated area for at least one day, or until the area is dry.