Leaf miner

by Richard Jones

I parked in a side street in Forest Hill last week and walking down to the Horniman Museum I noticed something odd with a small Norway maple, Acer platanoides, growing in a rather untidy hedge.

Leaf mine on acer leafI parked in a side street in Forest Hill last week and walking down to the Horniman Museum I noticed something odd with a small Norway maple, Acer platanoides, growing in a rather untidy hedge. Some of the leaves were dappled with the pale blotches of leaf mines. I'm not an expert on mines, but it just didn't look right. I think I must never have seen these delicate angular leaves attacked so.

My first thought was that the mines had exactly the same shape and form as those scarring the horse chestnuts all over south London, caused by caterpillars of the tiny moth Cameraria ohridella. Sure enough, the maple was growing right next door to a horse-chestnut so heavily attacked that it had browned prematurely for autumn.

It turns out that this recent invader does also sometimes 'very rarely' feed on maple. When I returned to the car a couple of hours later I also saw the mines on sycamore. I hope this doesn't get anyone too worried.

The moth was first found near the Ohrid Lake region of Macedonia (former Yugoslavia), in the late 1970s, but was not identified until 1986. It has been spreading through Europe until it arrived here in 2002. No one knows quite where it came from, though there are several members of the genus in North America. There is a ray of hope for those contemplating a Europe without conkers. If it has had time enough to adapt to new foodplants, it ought also to have had time to be detected and attacked by our native parasitoids.

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Gardeners' World Web User 28/09/2008 at 09:28

There is a horse chestnut at my children's school gates in Jersey that is brown, with crisp leaves falling, when it should still be green, with fat conkers falling and being discovered with joy by the children. The tree has provided us with shade from the sun and rain, the children play around the trunk, and I can't be the only one thrilled each spring with the dramatic way it comes back to life from its winter dormancy. Hearing that this tree was being attacked by leaf miners and would probably die really disturbed me. It's more than just a plant, it is such a part of the school community.

Gardeners' World Web User 30/09/2008 at 12:42

The tree will not die because of the leaf miners. Yes, they must exert a terrific herbivore load on the tree, but as we can see from trees on the European mainland, which have been mined for 30 years, they still come into leaf, blossom and produce conkers every year. What may happen, over time, is that trees become weakened, and so mortality to other diseases and stresses may be increased. Also, mature trees are much more able to withstand insectivore attack than seedlings or saplings.

Gardeners' World Web User 11/10/2008 at 00:29

My area in Surrey has also been badly affected and we haven't seen many conkers. I was wondering what is happening to the oak trees? Outside my gardenwall and overhanging my garden are three oak trees.This year and progressively worse since previous years my garden has not only been showered in oak apples moreover with very abnormal acorns, if you could call them that. Most years we get "some" very angular,sticky, brown, misshapen acorns, but this year I haven't seen a single normal acorn. It is quite obviously caused by insects but it is very worriying not to see a single healthy acorn. The leaves that are now landing are infested by scale insects and my patio looks like it's covered in split green lentils. Trees are normally more susceptible to attacks if weakened. My house was built 4 years ago, could it be that the trees were damaged in some way and will they recover if so? I am of course concerned about the affect it may have on my garden as I have planted it from new.I spoke about the oaktrees to a fellow gardener who has oak trees in his garden and he has the seen the same problems. Any comments please!

Gardeners' World Web User 14/10/2008 at 08:29

Reply to Leaf Miner. The oaks are affected by the knopper gall, Andricus quercuscalicis, a growth on the acorns stimulated by the presence of the eggs and larvae of this tiny gall 'wasp'. www.rhs.org.uk/advice/profiles1005/knoppergall.asp When it first arrived in the UK in the 1960s there were great worries that it would destroy all the acorns on Quercus robur, since heavy infestations appear to leave no single acorn 'true'. But the oaks are still producing fruit and there is no sign of them failing to produce offspring. Oak trees are very long-lived organisms and are able to suffer many years of galls, acorn feeders and other 'pests'. Keep a look out for the next 2 decades and you will see some years are good for galls, others good for acorns.

Gardeners' World Web User 13/10/2009 at 16:35

I have grown an oak tree from an acorn in my greenhouse, i have nurtured it and gave it a lot of tlc, i now find that it has been attacked by something, i know not what, the leaves started to brown and are all but skeletal, the plant is not dead but i am beginning to worry about is there any one out there that knows what it is and a possible solution.

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