TCM tests cast doubt over Japanese knotweed approach

Injecting large doses of glyphosate herbicide into Japanese knotweed may not be the best control method, says weed-control company TCM following tests.

The firm carried out five-year trials employing the 5ml per stem dosage of 360g per litre concentration in some parts of a test site and lower concentrations in others.

One of the main TCM findings from its research was that at the 5ml rate per stem the majority of the rhizome system in the topsoil was dead after three years, but any at a depth of more than 60cm was alive.

Owner Howard Downer said the excessive 5ml/stem dose rate was possibly eliciting a dormancy response that could be linked to knotweed's status in its native ranges as a pioneer coloniser of barren volcanic slopes.

He added that killing old rhizomes and all their reserves of dormant buds will "be the key to the eventual eradication of knotweed", while foliage spraying, excavation and screening are all effective methods.

Downer said lower herbicide concentrations encouraged TCM to believe that dormancy responses can be avoided and more thorough translocation promoted.

He added that TCM is working with Santander on mortgages refused because of knotweed and has succeeded in 42 cases so far this year - double the number in 2011.

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