A method of controlling the growth of a plant is provided, the method including the steps of: (a) inserting a capsule containing an agent into an opening formed in a plant; and (b) closing the opening formed in the plant into which the capsule is inserted. The agent may be a chemical agent. The plant may be a woody plant, such as a woody weed or a woody cultivated plant. Also provided is a capsule containing an agent for insertion into a plant, and an apparatus for insertion of a capsule into a plant.