Posted at February 9, 2011 in News by JHPS Gardens

Japanese Knotweed Vs psyllid Aphalara itadori  


Britain is quite fortunate when it comes to having invasive plants because as a country we have very few. However one in particular called Japanese knotweed (Fallopia japonica) is one of the worst invasive plants that Britain has to contend with regarding the amount it would cost to eliminate them on a national level and even then it would not be guaranteed.

Control methods
Many companies may try to sell you a chemical or mechanical method to use on Japanese knotweed but none of these methods offer long term control over the Japanese Knotweed. On the contrary an affordable and practical method is biological control; this is a method where a natural enemy of the Japanese knotweed from its native country Japan is used to control its growth.
Japanese knotweed in Britain has only come from one introduction and so it only has one single clone (female). So it would not be able to reproduce by seed and has no genetic variety, so if it were challenged by a pest or a disease then the chance of it developing to get out of trouble is highly unlikely.
We at JHPS Ltd have had success eradicating Japanese Knotweed from sites in Cheshire, if you would like us to quote for the removal of Japanes Knotweed please get in touch on our free phone number 08000 937926 or at our head office 01782 396168  
Although it would be hard for it to reproduce if threatened by pests or a disease, the Japanese knotweed has plenty of viable seed. The most common pollen is from Russian vine (F. baldschuanica), however you would think that both of these would produce a hybrid nightmare but the seedling from this hybrid hardly ever establish themselves. There is another relative the giant knotweed (F. sachalinensis) this causes less trouble than Japanese knotweed but the hybrid produced is F. x bohemica is no worse than the Japanese knotweed and not very common.
Biological Controlling – The Testing
For this last decade the Centre of Agricultural Bioscience International (Cabi) in Oxfordshire has been hard at work trying to find the right biological knotweed killer. Cabi is backed by a large number of associations. As this is the first time that biological controlling has been tried in Europe, Cabi is obviously worried that something may go wrong.
On the other hand Cabi had no problem finding possible plant-eating insects, which like Japanese knotweed. They were able to do research over all four of islands of Japan, they were able to find 186 possible insects but all were shown that they would not work to the full extent that they wanted. There were possible ones like a leaf beetle, this reduced the Japanese knotweed in no time to nothing more than a skeleton however this particular beetle did not just eat Japanese knotweed but other common plants in Britain.
Possible Enemy Found
Eventually they were able to find psyllid Aphalara itadori, a jumping plant lice. This particular psyllid Aphalara itadori showed that it would do a lot of damage to the knotweed plants, especially Japanese knotweed, giant knotweed and their hybrid. Many tests were carried out to make sure that theAphalara would not eat anything other than knotweed. They made sure that they tested plants of the same family, related crop plants, native and introduced plants, a few plants that looked a bit like knotweed and unrelated plants, as precautions.
Many test were done on the selected plants, looking at all areas that could cause problems, like if an egg were laid on test plants would they survive or if they hatched would they survive. Also would adults survive on the test plants? The psyllid Aphalara itadoripassed all these tests showing that they would not eat, lay eggs on anything but Japanese knotweed or the hybrid. They would also survive on giant knotweed but they did not take to it as eagerly.
Winter Time
Japanese knotweed is herbaceous (dies at the end of the growing season), as a result the psyllid Aphalara itadori has to find somewhere to spend the winter. When they are in there native environment in Japan they spend the winter in foliage or crevices in the bark of conifers. So in Britain they would try and find somewhere similar to their normal environment, but not worry there is no evidence to show that they feed on or damage the plants they spend their winter in.
The psyllid Aphalara itadoriwas realised to specific areas in the spring of 2010, they are being monitored but it will take at least a year before they know if they have established successfully. But for the time being Japanese knotweed may possibly become less common.
At JHPS we use a systemic weed killer to kill off Japanese knotweed, this particular weed killer is unavailable to the general public. We have used this method on many different sites and gardens where we have had success using it. Hopefully in the future when psyllid Aphalara itadori has been tried and tested we will be able to use it along with our other methods. If you would like more information on Japanese knotweed please contact us on one of the following: –
Free Phone: 0800 0937926
Head Office: 01782 396168