pq75's picture

Japanese knotweed leaf damage?

Observed: 17th August 2013 By: pq75pq75’s reputation in Plantspq75’s reputation in Plantspq75’s reputation in Plants
Japanese knotweed leaf damage?
Japanese knotweed leaf damage?
Japanese knotweed leaf damage?
Japanese knotweed leaf damage?

Hi, can anyone help with id of what is causing the red blotches on the leaves of this Japanese knotweed? is it a leaf miner?

Species interactions

No interactions present.


lavateraguy's picture

A biological control agent ...

... the psyllid bug, Aphalara itadori, was released in the Swansea area in 2010. I wouldn't have expected it to have reached Cheshire, but supposedly the reason Japanese knotweed is such a problem is that nothing (else) in Britain eats it. (I do wonder why goats can't be used.)

Googling finds me a site that implicitly says that there are no leaf-miners of Japanese knotweed in Britain. (There are a couple of species which attack Russian vine.)

Mydaea's picture

Phytoliriomyza melampyga is a

Phytoliriomyza melampyga is a miner in Japanese knotweed in UK and is not uncommon. This does not look like it though.

[Edit in the cold light of day] Ignore that irrelevance above - a senior moment, I was seeing Japanese knotweed and thinking Himalayan balsam.

Wildlife Ranger's picture

Balsam Leaf Damage

There is only one miner I think in the British Leaf Miner site that utilises Himalayan Balasam


However this looks like a different infestation


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Rachy Ramone's picture

I'm just delighted...

...to see that something can actually eat the blasted stuff!

Actually, some superficial internet research suggests that goats eat it, but only the foliage, which doesn't kill it. Sadly.

Garden Organic (http://www.gardenorganic.org.uk/organicweeds/weed_information/weed.php?i...) suggest that "sheep, goats, cattle and horses" will all eat the new shoots.

I imagine the problem with using goats as a control is to get them in the right area at the right time: and then to prevent them eating everything else in sight!

Rachy Ramone

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Field Guides for Budding Botanists:

lavateraguy's picture

I have read ...

... that continued mowing will see off the knotweed (but you have to avoid spreading the plant in the process), so that I imagine that letting goats eat off the new shoots at regular intervals would do the trick. I imagine that one would tether the goat in the middle of a patch.


cabbageleek's picture

Herbicide damage

This looks like mild herbicide (glyphosate?) damage to me.

pq75's picture

mild herbicide (glyphosate?) damage

Thank you