Mersey beetles try Knotweed diet

Japanese Knotweed Solutions have been tasked by the CABI with bringing them information on the recently released Psyllid aphid ‘Aphalara Itadori’ (the Japanese Knotweed Psyllid), so we’re always on the lookout for evidence of abnormal Japanese knotweed plants.

The Japanese Knotweed Psyllid is brown in colour and about 2mm long – similar size to the green aphids you see on house plants in the UK – so it’s pretty hard to spot. Its young suck the sap from the stems of the plant, leaving it depleted, so we’re on the lookout for stunted plants and withered stems.

One of our team found some evidence of some pretty severe leaf damage near the Mersey River this weekend, and brought these photos in:

As we suspected, the hungry beast in question was not the Psyllid, but the beetles in the photo. The identification was made by our contact at the CABI, who said:

“This is almost certainly Gastrophysa viridula, the green dock beetle, which normally feeds on Rumex species but it is rare to see such damage in knotweed this early in the season.There must be some pretty hammered dock nearby.

There is indeed some “pretty hammered dock” nearby, as you can see on the right and in the background of the next photo:


In the long run, it’s probably too much to hope that the green dock beetle can be a significant help in the fight against knotweed, but it’s still nice to see that knotweed isn’t having it all its own way.

So there was no sighting of the Psyllid this time, and it’s proving harder to introduce to the UK than people might initially have hoped, but sooner or later you could be noticing some stunted Japanese knotweed near you and wondering whether our new Japanese friends have arrived in your neighbourhood.

If you suspect that you have spotted the Psyllid aphid, feel free to email a photograph to our team at [email protected] – though as always, we advise people to take care not to disturb Japanese knotweed, or remove any part of the plant from site.

Alex D