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We have done considerable research onto stem injection techniques while working as knotweed contractors for Camden Council and have found the method to be extremely effective. We normally monitor knotweed infested sites for 3-5 years and on many occasions we have found that the injected herbicide has been 100% successful after just one visit.
It is an ideal technique to use in surburban gardens and park land were excavation is not feasible. Another advantage of stem injection is that it keeps the herbicide within the plant - surrounding waterways and other plant and animal life will not be affected.
Guide to Japanese Knotweed for Developers produced by the Environment Agency
Japanese Knotweed Code of Practice produced by the Environment Agency
JK Guidance ID and Control produced by the Cornwall Knotweed Forum were JK is rife
Watch this BBC video on the current state of Japanese Knotweed Removal Methods
Stem injection must be done on healthy flourishing plants during the growing season, April to October. The plants are injected with a measured dose of concentrated herbicide, just below the third node on the stem. On a flourishing plant this will be around the one metre mark. Knotweed stems are hollow and the herbicide will quickly be absorbed by the plant all the way down to it's rhizome (root) system.
Stem injection is a lot quicker, cheaper and more effective than spraying and targeted foliar application (brushing on the herbicide directly onto the leaves). The technique is often 100% effective with just one visit but the site will need to be inspected and any remaining shoots treated over a one or two year to ensure that eradication has taken place. It is this time constraint which makes stem injection unsuitable as a technique for property development. On construction sites, ground excavation is normally the preferred method.
Give us a call for some friendly help and advice.