Its a moth not rust that’s affecting our conker trees
Have you noticed whitish patches on the leaves of horse chestnut tree, which by the middle of summer, the whitish patches die and turn brown and you may believe that autumn has come early for the tree. Sometimes whole trees turn brown, and it looks like autumn has come early. I have seen many trees displaying this rust type markings on horse chestnut trees. I suspect many of you have too. Leaf fungus blotch looks similar but see the differences here
Our conker trees are under attack by ‘alien’ invaders!
The damage is caused by a tiny ‘alien’ species of leaf mining moth, the Horse Chestnut leaf-miner, Cameraria ohridella, which was first found in Britain at Wimbledon, SW London in 2012. It is thought to have been expanding here due to accidental transportation by man. That sounds familiar! It is another alien species that has arrived in Britain. For biologists, an ‘alien’ is a species not naturally found in an area or habitat.
Purists will stay the horse chestnut is an alien anyway!
According to the Woodland Trust, Horse chestnut, Aesculus hippocastanum, is a non native as it was introduced here from Turkey in the late 16th century and widely planted. I am presuming because of the candle like flowers, which incidentally are pollinated by insects including bees which visit it for pollen and nectar! Forest Research state that there are an estimated 470,000 trees in Great Britain, with most of them found in non woodland sites and commonly found in parks, streets and gardens as amenity trees.
Besides the moth’s caterpillars eating the leaves from the inside, which causes the rusty brown marking, infected trees are weakened, and produce smaller conkers, due to the shortened period of photosynthesis. Researchers found that the moths affect the seed quality but not quantity and that the number of flowers per tree did not change, which is good news for our bees! The trees also have to contend with Bleeding canker now a serious disease that is increasing in the UK.
Fortunately, there may be help at hand. Some of the leaf-mining moths are killed by birds that prey upon the caterpillars. Others are killed by natural pest controllers, in the form of tiny insects. These insects lay their eggs inside the caterpillars of the leaf-mining moths, and when the eggs hatch, the larvae slowly eat the caterpillars, eventually killing them.
From 2010 we have been inviting people to take part in real science to discover more about conker tree health by taking part in our missions. From 2014 we have set up a recording page for the leaf-miner, and have set up the missions as stand-alone activities, ideal for school children.
Get invovled in real science!
The Conker Tree Science project is real science: the frst scientific results of the Conker Tree Science project were published in the scientific journal PLOS ONE. Find out about the results
Find out more about how to take part
For more information about this topic visit Conker Tree Science
This video below by the Naked Scientists show you what the larvae look like.
Leaf miners in Horse Chestnuts film
With thanks to Dr. Michael Pocock for permission to use this material