Japanese Knotweed

RHemmings

Dustyevsky said:

Dream homes don't come with thoughts of selling in the future, unless it's with the prospect of a substantial profit! For most of us, they arrive with problems, which we either decide to accept, or we let someone else have them.

JK can be treated, and in time, eradicated, but like subsidence, some stigma remains long after it's gone. The watercourse makes things trickier, but the treatment, glyphosate, is approved for use in watercourses.

For me, the matter of how the brook goes under the house is important. In a concrete or plastic pipe, no problem, but I'd also want to look at flooding potential & history. Assuming those yield satisfactory answers, I'd regard the JK as an extra expense and re-negotiate accordingly. As you say, a guarantee is better than the cheapo solution applied by the vendors.

When you say that glyphosate is approved for use in watercourses, I thought that it was illegal to use herbicides of any sort too near to a watercourse. If this is the case, then it makes it more tricky to treat the JK if it is near to a watercourse. As permission would be needed, which may not be granted. 

https://www.progreen.co.uk/problem/aquatic-weed-control

The Department of Environment, Food and Rural Affairs (DEFRA) enforces strict rules on the use of herbicides in aquatic areas. Using any herbicide product in/ near a watercourse requires Environment Agency approval; contact your local EA office before work begins. A form is available online to fill in to seek approval for spraying pesticides in watercourses: AQHerb01.

Dustyevsky

Chemistry777 said:

Haha !!!! yes the German version except the yellow stuff.  Spreads like wildfire and proving difficult to get rid.

Ah, that one has an Underground Resistance. Sympathies.

RAS

The best time to treat JK is by injection in very early autumn. If that's done carefully when a period of dry weather is predicted, there shouldn't be any pesticide escape. It's how the National Trust treat areas.

What is of more concern is that tiny remnants are boosted by wet weather. 

We treated an area away from a water course over several years that had been dragged along by contractors installing a security fence. All gone for nearly a decade but this spring two stems have popped up. Admittedly one was the last to die off because the land user kept pulling it up before it could be treated.

GDB2222

Whether or not JKW has been overhyped as a problem, it is still a problem. You will have ongoing work to get it under some sort of control. That could mean significant bills over the years. 

Whilst the sellers have not covered this up, you negotiated the house price without knowing about the JKW. It’s a significant defect, and the sellers must be expecting you to renegotiate. The question is how much is reasonable?

alanyau88

From what I've read, it could possible shoot up in your living room flooring and it grows many cm in a matter of minutes.  Frankly, I would not gamble with my retirement life and live in a place that has japanese knotweed.  The resale value would plummet.  Plenty of other dream homes that I would be just as happy.  If you realised you were climbing up the wrong mountain and you were about to reach the top, would you still want to stay on that mountain?

Smudgeismydog

Just popping back to provide an update. The current owners have provided evidence of treatment over the last couple of years through a local environmental agency, with a further treatment due in September. The surveyor we instructed also confirmed there is no visible evidence of the plant on site.

However, the current owners have not put an ongoing treatment plan in place, which are available with guarantees that would meet insurance and mortgage provider requirements, so we’ve negotiated a discount on the price to allow us to organise this ourselves.

We have also spoken with people who’ve had JK on their properties and effective treatments are much more widely available now. 

We are comfortable with this outcome and are proceeding with the purchase, thanks for all your comments, it’s appreciated.

Sapindus

alanyau88 said:

From what I've read, it could possible shoot up in your living room flooring and it grows many cm in a matter of minutes.  Frankly, I would not gamble with my retirement life and live in a place that has japanese knotweed.  The resale value would plummet.  Plenty of other dream homes that I would be just as happy.  If you realised you were climbing up the wrong mountain and you were about to reach the top, would you still want to stay on that mountain?

JK is tricky stuff but no plant grows "many cm in a matter of minutes" and it won't go through sound concrete, it exploits existing cracks and weaknesses.