Horsechestnut (probably) leaf miner moth (maybe)

[Brij]

Well, we have 3 poorly trees in the house we just moved into. We pulled the ivy that was climbing up by the roots, but on closer inspection, it doesn't seem to have been enough to cause the substantial damage to the leaves of the tree.

So after a bit of online research, I'm fairly confident the trees are horse chestnuts. There is no fruit (otherwise I'd have known), but that might be because they are so very unwell. They have more pear-shaped leaves than most of the pictures of horse chestnuts I have found online, missing the 'pointy bit' shown on most of the leaf tips, to use the devastatingly technical term. However, I have found a few pictures that match our invalids.

And after a bit more research (and poking around and shrieking when I found wriggly things), I think we have the leaf miner moth, which seems rather notorious. It looks a bit like the leaves are sort of separating into a green layer and a brown layer. The brown layer is significantly thinner than the green layer, and covers the green layer on the top side. When you peel the brown bit back, there are roughly spherical blisters on the leaf, off-white in colour, which contain a tiny brown wiggly thing, a bit like a tiny caterpillar. The creatures are between 1/8-1/4" in length.

I will post pictures to confirm the diagnosis when I've tidied up enough to find the cable, but for now, I was wondering if anyone knows of treatments? I haven't found much via google other than importing carniverous wasps, which I must say doesn't appeal. If you guys know of any child-friendly options, so much the better - there is a 5 year old here that rather likes to pick off bits of plants to taste and batter his older brother and au pair with. Though he is usually supervised in the garden.

[george]

Your description definitely sounds like a leaf miner. The wiggly thing is the larval stage of the moth. However, apart from making the leaves look kind of ugly it seems that the bugs don't actually cause significant damage to the trees.

Here is a good source of information about them.

http://www.forestresearch.gov.uk/leafminer

Hth

George

[Brij]

Thank you George! It's amazing that the tree isn't severely damaged - I would imagine that its photosynthesising capability has been reduced by at least 50%!

We'll compost the leaves as soon as they fall to try to reduce the impact for next year.

But one last question...

Does this mean that when the pupae all hatch, the garden will be swarming with moths?

[george]

It is amazing how much damage can be done to plants and for them still to be doing fine. I think it is because they evolved together with insects that way.

Does this mean that when the pupae all hatch, the garden will be swarming with moths?

Maybe. It depends on how synchronised the emergence of the moths is and also how long the moths live for. You might have loads or you might not really notice them.

You could probably reduce the moth emergence (and problems next year) by taking off the infected leaves which you can reach and composting them now.

[Cobnut]

But one last question...

Does this mean that when the pupae all hatch, the garden will be swarming with moths?

If they're anything like the holly leaf miner they will be predated on by a parasitic wasp, plus a fair few will fail to hatch for various other reasons. I doubt you'll even notice them.

[donegalwildman]

Yup....the Horse-Chestnut-specific micromoth Cameraria ohridella has been progressing northwards for a few years. Any parasitica haven't yet caught up with them, but when they do it will be the usual see-sawing act where either the host or the parasite is around in larger numbers at any one time. The adult moths are minute and won't be at all bothersome. (But of course, they have every right to be there....;)....keeping your wasp post in mind)