Stem­ming the Ja­panese knotweed in­va­sion

EADT Suffolk - - Inside - Howard Downer is MD of To­tal Con­ser­va­tion Man­age­ment (TCM) and has more than 20 years ex­pe­ri­ence in the in­va­sive weeds sec­tor. To find out more, con­tact him on 01787 278086 or 07771 623276, visit www.Tcm­knotweed­ser­

JA­PANESE knotweed. If you have it on your property and want to sell or re­mort­gage you are likely to know how this tall, ver­dant shrub, with white flow­ers in late sum­mer, can all too eas­ily al­ter your plans, and even wipe value from your property.

Ja­panese knotweed was brought to Europe in the 1840s by a Dutch hor­ti­cul­tur­ist who, in turn, sent plants to the Royal Botanic Gar­dens in Kew in 1850. This pre­vi­ously un­seen plant suited the new Vic­to­rian style of wilder, softer gardening and it be­came a pop­u­lar, and prized, spec­i­men plant. Shar­ing cut­tings, and the plants travel through water cour­ses and con­tam­i­nated soil be­ing moved for con­struc­tion and road build­ing meant that by the late 1800s Ja­panese knotweed had be­gun its in­va­sive path. In 1981, it was one of only two plants, the other be­ing Gi­ant Hog­weed, that was pro­scribed in the Wildlife and Coun­try­side Act, mak­ing it an of­fence to “plant, or oth­er­wise let grow, in the wild”.

All Ja­panese knotweed plants in this coun­try are fe­male, so is it un­able to re­pro­duce via seed. Its re­lent­less march across river­banks, rail­way lines, waste land and into our back gar­dens has been caused by hu­mans. In 2017, re­search from the Crop Pro­tec­tion As­so­ci­a­tion re­vealed that it is cost­ing property own­ers thou­sands of pounds each yea – 20% of those sur­veyed said it had low­ered the value of their home, and 60% re­ported that the weed had dam­aged their gar­den or de­stroyed some­thing on their property.

Many myths abound about this per­ni­cious weed. It can­not grow through con­crete but it can grow through voids within con­crete, or cracks in foun­da­tions or tar­mac, through drains and gar­den walls. It is not il­le­gal to have Ja­panese knotweed on your property but it is il­le­gal to al­low it to spread. If you do you could end up in a costly le­gal dis­pute with your neigh­bours. It is true that mort­gage com­pa­nies are loathe to lend on a property if Ja­panese knotweed is present. To do so, they will re­quire a Ja­panese Knotweed Man­age­ment Plan along­side an A* rated In­sur­ance Backed Guar­an­tee (IBG), both of which will be avail­able from a rep­utable Ja­panese knotweed erad­i­ca­tion com­pany.

If you do have it on your land, don’t wait un­til your prospec­tive buyer’s sur­veyor spots it and the whole house move splut­ters to a halt. Get or­gan­ised quickly – now is the per­fect time of year as the plant will be­gin to push through the earth in March and April. New shoots, which of­ten look rather like as­para­gus, have a red or pur­ple tone. They sprout up

‘In 1981, it was one of only two plants, the other be­ing Gi­ant Hog­weed, that was pro­scribed in the Wildlife and Coun­try­side Act, mak­ing it an of­fence to “plant or oth­er­wise let grown, in the wild”’

from the rhi­zome which can be up to three me­ters deep and lie dor­mant for many years. As spring pro­gresses the plant grows rapidly. The bam­boo-like stems are hol­low, and of­ten speck­led red, or with red joints and knots. By sum­mer the plant can reach over three me­tres high and will be cov­ered in lush, green, shield or heart-shaped leaves up to 22cm long. In late sum­mer it de­vel­ops clus­ters of spiky stems cov­ered in tiny white flow­ers. In late au­tumn, the leaves fall and the canes go brown. But be aware, it is not dead, it is stor­ing en­ergy deep in the rhi­zome ready to re­peat the process the fol­low­ing year.

Treat­ment op­tions – her­bi­ci­dal and, as an or­ganic al­ter­na­tive, but not ap­pro­pri­ate for all sites, dig­ging it out. The chem­i­cal route takes a num­ber of sea­sons to com­pletely erad­i­cate all parts of the plant. It is pos­si­ble to sell your home while this is go­ing on, with the caveats re­lat­ing to Man­age­ment Plans and IBGs. For an av­er­age res­i­den­tial in­fes­ta­tion erad­i­ca­tion should cost in the re­gion of £2,000 - £4,000.

With the right equip­ment, the plant and the rhi­zome can be dug out. The rhi­zome is brit­tle and a piece left be­hind, just the size of a fin­ger­nail, will re­gen­er­ate. It is an ex­pen­sive method and may not be suit­able where ac­cess to the site is dif­fi­cult. The soil, rhi­zome and canes can only be dis­posed of in a li­censed land­fill, as it is clas­si­fied as con­trolled waste, just as any canes you cut down in your gar­den can­not go into the coun­cil re­cy­cling bins.

Don’t be fooled into think­ing it’s dead in win­ter - it’s sim­ply get­ting ready to re­turn

By sum­mer Ja­panese knotweed will pro­duce spikes of small white flow­ers

Look for red­dish brown as­para­gus-like shoots in spring

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