During winter, above ground stems and foliage die back as the plant enters a phase of dormancy. But underground rhizomes remain active, storing energy reserves the plant will draw upon for rapid, robust regrowth in spring. The diminished vegetation makes winter an ideal time to cut back knotweed stands and prepare infestations for follow-up herbicide treatments when the plant re-emerges.

Physical Removal

Manual cutting of knotweed during winter has multiple benefits for containment and control. Removing dead stalks and stems clears the area, making it more accessible and giving a clean slate for spraying or digging activities later on. It also reduces the risk of fragments being unintentionally spread during control efforts.

Careful timing is important though, as any cutting or mowing done after dieback but before true dormancy can actually stimulate growth. When cutting, do this 10cm above the ground to avoid the spread of rhizome. Start winter cutting only after several hard frosts have induced full senescence, indicated by completely brown, withered stems. Repeat cutting may be needed through winter to clear regrowth.

All plant material should be disposed of properly, either via composting, deep burial, or incineration, as segments left behind may re-sprout. Avoid pulling underground rhizomes which can break off and spread. The goal is clearing aboveground vegetation while keeping rhizomes intact for later treatment.

Herbicide Planning

While foliar herbicides are ineffective during winter when there’s no green growth to absorb chemicals, it’s an ideal time for planning applications. Surveying knotweed stands without obscuring foliage makes it easier to delineate the full extent of infestations across a site. This allows creating accurate treatment maps indicating the precise locations needing herbicide.

It’s also helpful to document stalk heights and densities as a gauge of infestation severity. Robust stems reaching over 3 metres signal a substantial, established colony requiring intensive management. Note any hazards like waterways that could be contaminated by chemicals to determine appropriate products and application methods.

Detailed mapping and documentation during winter gives a head start on spray plans so herbicide treatment can commence promptly when regrowth appears in spring. This takes advantage of early emergence when knotweed is most vulnerable.

To be most effective while using foliar herbicides should be used later in the season ideally after flowering. August, September and October.

Prevention and Containment

Even though the they are winter canes and the Japanese Knotweed appears dead they should be treated as controlled waste, they can be incinerated on site or stamped down and mulched in the area they are growing.

While winter offers opportunities for control efforts, it’s also critical for preventing further spread. Knotweed rhizomes can be accidentally transported in soil removal and landscaping work, so construction and digging should be avoided in and around infestations during dormancy, when new growth is not apparent.

Vigilance is also needed along waterways prone to winter flooding, as flowing water can dislodge and spread fragments downstream to form new colonies. Installing silt fencing and barriers around existing stands curtails spread by containing rhizome movement, supporting long-term management goals.

By taking advantage of Japanese knotweed’s winter dieback to execute preparatory cutting, herbicide planning, soil injection, and containment, land managers can implement a targeted, multi-season control strategy. Ongoing diligence is vital for combating this challenging foe. But concerted effort during winter provides a solid foundation for making headway against knotweed’s tenacious grip.

The post Tackling Japanese Knotweed Infestations in Winter appeared first on Conservation Land Services.

Japanese knotweed in the Winter

As the plant prepares to die back (not die altogether) in the autumn months it will lose its leaves like those of deciduous trees and moves all of its nutrients down into its rhizomes, a series of underground roots and shoots. (it can spread at length depending on the maturity of the plant and the soil conditions).

Introducing herbicide at this critical point is considered to the most effective time as the plant is drawing down the nutrients into the crown and rhizome. This should be done by a professional invasive weed specialist. If you have any concerns, reach out for  a survey of the affected area.

Plants with rhizome systems like Japanese knotweed will preserve their energy and survive under the soil until more favourable conditions return. Knotweed typically will begin to remerge in about April.

Identifying Japanese knotweed in winter months

Japanese Knotweed with its hollow, purple stems and heart-shaped leaves gives way to dry, brown and brittle stalks with a dark orange centre. The canes are hollow and will collapse around each other as they die. The winter is more difficult for untrained eyes to identify Japanese Knotweed than other times.

The best method of identification in winter is a close examination,  highlighting the stems which zigzag as they grow and the aforementioned brown and orange colouring which makes them look a bit like dark bamboo canes.

You should be especially careful when investigating a suspected invasive plant species, not just because some of them can cause harm to humans but also because there is a real possibility of spreading the plant to other unaffected areas.

Take care not to spread the plant:

• Kick off any mud and vegetation from your boots
• Check your clothes for any knotweed fragments
• Call an expert for advice and confirmation

Sources

Source: UK Gov Guidance https://www.gov.uk/guidance/prevent-japanese-knotweed-from-spreading

Source: RHS weeds https://www.rhs.org.uk/weeds/japanese-knotweed

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The post Why Japanese Knotweed in the winter is a good time to spot and treat it? appeared first on Conservation Land Services.