Japanese Knotweed Report from Cllr. Lindy Foster Weinreb As members will be aware the invasive Japanese Knotweed has established itself in the River Bulbourne by Berkhamsted Photographic in the wetland area adjacent to Broadwater Lock. We, as a council, have put aside £100 a year for the next three years to eradicate it. Unfortunately, as can be seen by the accompanying quote, we allowed substantially insufficient funds. The land concerned is the joint responsibility of British Waterways, the Environment Agency and County (as it has now spread on to the highway). It has been extremely difficult to get anyone to accept responsibility which is why the Environment Committee very sensibly decided to fund its removal. The quote we have is far greater than the money we have put aside. I have managed to persuade British Waterways to pick up and run with the problem from the Autumn onwards. This leaves us with an urgent problem immediately. The first two stages of the treatment which should start immediately would cost £175 each. I would like to propose we make £350 available immediately. British Waterways will then pick up the problem and costs involved after that. Control Measures The main problem with the spread of the species is that once it becomes firmly established in an area it is difficult to eradicate. One means of ensuring that the species does not get a chance to become firmly established is to monitor areas of particular concern. Such activities can be conducted by naturalist groups and staff at parks and wildlife preserves. If small clumps of Japanese knotweed are discovered, these can be carefully dug up, making every attempt to remove all sections of the rhizomes. Even small sections can serve as propagules for another generation of plants. Continued monitoring is necessary, after removal, to ensure that any new shoots arising from missed portions of the rootstock are subsequently also removed. When clumps have become sizeable it is futile to attempt to dig up plants. Such activity would inevitably result in sections of rhizome being missed and many separate underground fragments being created, each of which would serve to produce a new plant. In addition, the removal of even a single large clump is so highly labour intensive that efforts to remove all underground portions of the plant would not be achieved. The extensive digging required to remove all portions of the rootstocks would result in a considerable amount of ground being disturbed and would encourage the development of either missed fragments of rhizome or the growth of other weedy species developing from the soil seed bank or from volunteer weed seeds arriving from nearby sources. The best means of control for Japanese knotweed is through repetitive cutting of the stems near the soil surface with the addition of spot application of a systemic biodegradable herbicide like glyphosate (e.g., Roundup, Rodeo; only the latter is approved for use near water). If no herbicide is applied, the act of cutting the stems near the ground during the early to mid part of the growing season results in depleting the food reserves stored in the rhizomes that are necessary to produce new aerial shoots. Several cuttings would likely be required during a single season followed by a similar treatment the following and perhaps subsequent years until no new shoots appear. The application of glyphosate by painting the cut stems with the herbicide is likely to be more effective and a more rapid means of eliminating the underground portions of the plant. Glyphosate can also be sprayed on the entire plant, taking appropriate precautions in applying the herbicide for personal health reasons and also to minimize spraying other desirable plants. Glyphosate is a non-selective herbicide. If plants are sprayed, the best time is late in the year when leaves tend to conduct nutrients to the rhizome as part of the build-up of food reserves to support growth the following year. Such general spraying is not recommended in nature reserves where other species may be impacted and because of the likelihood that repeated applications may be required. Picloram has been recommended as a selective herbicide for use with Japanese knotweed by the Nature Conservancy Council. However, this herbicide is persistent in the soil and is also not to be used near water. |
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Berkhamsted Citizens Association Berkhamsted Town Council Berkhamsted Youth Council British Waterways Dacorum Borough Council Environment Agency Groundwork Hertfordshire Herts and Middlesex Wildlife Trust Inland Waterways Association |
