Japanese knotweed is a perennial shrub that can grow up to a height of ten feet and a form a dense thicket. They pose as a great threat to natural vegetation and they can significantly alter the ecosystem if they are not controlled. They are very persistent and can survive in adverse environmental conditions such as extreme temperatures and salinity. Once they are fully established they can be very difficult to control.
The best control method for Japanese knotweed should have a watershed approach. This is because the primary dispersal means is through moving water and streams which transfer seeds and plant fragments to areas that are not affected. Knotweed commonly infests wetland areas that are adjacent to streams and water points making plans to control them even more complex.
Mechanical, manual and chemical methods that have been used in the past have had varying degrees of success in effectively controlling the spread of this weed. Manually removing grown knotweed exposes the ground to sufficient light and as a result causes them to sprout again in the subsequent year. This means that the outbreaks have to be dealt with every other year.
Japanese Knotweed Ltd, who provide Japanese Knotweed removal in Manchester, say that just like any other invasive species, knotweed needs to be carefully mapped and areas where they are dominant identified. They then have to be eliminated in their early stages before they are completely established.
Mechanical control is effective in environmentally sensitive areas or places where chemicals and herbicides cannot be used. This process involves uprooting rhizomes, mature plants, seedlings and consistent clipping. A lot of precaution should be taken especially with plants that are more than half an inch. This is because they have the capability of sprouting again if they are disposed carelessly. Plant parts should not be allowed to find their way to streams and waterways. The roots and stems should be completely dried in places where they are not in contact with soil. Disturbed soil can support invasion and it should be minimized as much as possible during this process.
Chemical control is mainly done by use of herbicides. The methods include wicking, spraying, injection among others. Integrated control methods such as cutting during spring time and applying herbicides during summer have been effective in areas that are close to water bodies. Glyphosate is sometimes used although it kills both grass and broad-leaved plants. Triclopyr is a selective herbicide that kills broadleaved plants but has no harmful effect on grass species.
Foliar treatment is usually used in cases where the control measures are not supposed to affect the species that are not targeted for eradication. This method is effective in summer when plants are actively transferring nutrients. This method is only practical on Japanese knotweed that is 3 to 6 feet tall. This method is not applicable for weeds that are 10 feet tall. Foliar application works well on small to medium sized patches of Japanese Knotweed.
When Japanese Knotweed has fully developed over an extensive piece of land, they may require a combination of manual, mechanical and chemical methods. These control methods may be required to be repeated over a long period of time so as to completely eliminate the weed.