Successful treatment of an invasive weed is often defined by the control methodology selected. This can only be chosen with knowledge of the invasive species and how it propagates. Put simply, if you understand how a plant grows and spreads, you can create an invasive weed control plan that will ultimately kill it.

Getting to the root of the problem.

Invasive weed control starts with the consideration plants can be, broadly speaking, split into two groups:

Group 1 – those that spread by their roots (Examples: Knotweed, Bamboo Horsetail)

Group 2 – those that spread by seed (Examples: Himalayan Balsam and Giant Hogweed)

Controlling invasive plants that spread via their roots

An effective way to deal with these types of plants is by using a herbicide that can translocate chemical through the plant to its roots. Often, treatment will need to be persistent with visits required during the growing season over the course of several years.

It is possible to dig out the roots or dig out the soil containing the roots. Taking this approach, it is important to understand how the target plant’s roots develop, what parts are invasive and their typical rooting depth.

The roots of invasive species can also be blocked using root barrier that can be installed both vertically horizontally. For example, vertical root barrier installation is recommended by the RICS to deal with cross boundary interactions.

The Invasive weed control of plants that spread via seed

When an invasive weed’s method of propagation is by seed, the treatment must focus on reducing the number of viable seeds to zero. The soil harbouring seed is often called the seed bank; it can be depleted when the target plant is stopped from flowering – the point at which the plant produces new viable seed. Via herbicide control, for example, it is possible to kill the target plant before it seeds. Then, with repeat treatment as regrowth occurs, eventually there will be no viable seed.

Successful control requires that you know the longevity of the target seed (how long it remains viable on the soil) and the extent of land that harbours seed. Once this is known the duration and scope for treatment can be determined.

Plants that spread by seed can also be managed through excavation. This requires that soil is removed to a depth that ensures no viable seed would be present. Since the seeds are very difficult, or impossible, to see excavation strict biosecurity (site hygiene) is needed which will mean good cooperation onsite by machine operators.


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