"Stem injection" has replaced foliar spraying as the preferred technique for treating Japanese Knotweed and its hybrids, Bohemian Knotweed and Giant Knotweed. To a lesser extent, it is also suitable for treating early mature growth and juvenile Giant Hogweed plants. Although more labour intensive and time consuming than spraying, stem injection enables targeted application of herbicide directly into the plant, even in the most sensitive of sites, with little or no impact on the surroundings. It is particularly suitable for the treatment of mature Japanese Knotweed plants and is often the only appropriate treatment method for challenging situations, such as along river banks.
The technique involves the delivery of a small dose of systemic herbicide, either neat or diluted, into the lower section of the hollow plant stem via proprietary injection equipment. The aim of this method is to have the herbicide drawn down into the plant's rhizome system, which is the only way of successfully killing the plants. By directly targeting the plant's rhizome, the length of the treatment programme can be reduced to as little as two years. In addition, because of the small doses of herbicide being used and the targeted nature of the treatment, the environmental risks are greatly reduced and the total quantity of herbicide applied accurately controlled.