Natural control of Japanese knotweed: BBC Radio 4 Today programme interview

Interview with CABI scientist Dr Dick Shaw, on BBC Radio 4's Today Programme, discussing the potential to control the invasive plant, Japanese knotweed, in the UK using a tiny bug. (23 July 2009)

Category:

Science & Technology

Tags:

• Japanese
• knotweed
• biocontrol
• invasive
• weed
• biological
• control
• Aphalara
• itadori
• psyllid

[hitachi088]

heres what i normaly do : i take wood ashes (the one that remain after you heated your house all winter) and you drop like 2-3inch thick of it all around the contaminated area (knotweed).spray some water on top to make the chemical penetrate into the soil. if you see some knotweed grow thru that (very rare) you either poison it with roundup or you can take it with your hand and remove it. remember to put some more hash each time you feel the need too.

[Gomba13]

If you want to try the sand and rocks experiment again, you might have good results if you contain the loose material (think giant raised bed or sandbox) and lay down lanscaping fabric underneath it (with overlap). But make sure the first thing that goes on the landscaping fabric is sand, a good three inches of it, so there is absolutely no sunlight poking through.

For landcaping cloth, make sure it is the sturdy, woven kind, not the cheap, perforated plastic weedblock sheet.

[Gomba13]

Putting plastic sheeting on it doesn't work because sunlight gets them going so strong they pierce the plastic. Putting loose material on them doesn't work because they can push through it and, again, reach the sunlight, at which point you lose.

In my opinion, only combining both a solid physical barrier (lanscaping cloth) topped with a uniform, heavy weight (raised beds, concrete tiles, etc.) works. It needs to be weighed down and kept in the dark.

I will report again in fall.

[Gomba13]

I think I know why the loose sand and rock solution didn't work. Your solution lets them grow through the sand and rocks as there is no solid physical barrier to stop them in their tracks, and they eventually reach sunlight, which is what you should avoid at all costs.

Upon removing last year's lanscaping cloth, I found that wherever growing tips hit the landscaping cloth, they bent sideways, but by the time they would have found the edge of the cloth, they shrivelled up for lack of sunlight.

[hitachi088]

@Gomba13 no, seems pretty good to me. in the pass i used 3feet of sands and rock on the top of the area. but that didnt worked well...

[Gomba13]

@hitachi088 If the smothering is secured permanently, the crown would eventually have to give out. This year, they are getting a double layer of landscaping cloth, a layer of sand and concrete tiles around the raised beds. They will have zero room to grow. It is intended to be a permanent solution, and it will be handled only occasionally, to change the landscaping cloth (every decade or so). This year, I only see new growth in between and not in last year's beds.

You have a better solution?

[hitachi088]

@Gomba13 .6 gram of root can wake up and form another batch of plant 10year after being stopped.

[Gomba13]

This is still in the works, so I can't say whether it is a reliable long term solution, but I have built 10 inch (25 cm) deep raised beds over my japanese knotweed infested backyard. I started by digging up most of the knotweed, then I laid down heavy-grade landscaping cloth and built the raised beds over that. Nothing grew out of there. So, I guess smothering is possible as long as you apply enough uniform weight and a strong barrier.

Whoever imported this nasty weed should be punished!