Pictures: BFW Vienna
Institute of Forest Protection

The Horse Chestnut Leaf Miner Moth (Cameraria ohridella)

Damage Evidence: From the middle of May light spots (Blattminen/leaf-marks) become visible on the leaves, they quickly get larger and lead in June to a clear brown colouring of the bower. From the middle of July the leaves can begin to fall off in a strong attack.

Biology : The pupae over winters in fallen foliage/ground. The moths hatch out between the beginning of April and middle May. The first flight lasts about 3-4 weeks. First the moths swarm in the lower trunk area and then congregate on the bark. The egg laying takes place on the top of the leaves. Their development to larvae lasts about 2-3 weeks. The first "mines" become visible at middle/end May. The larvae "mine" in the leaves, here also the pupae stage occurs. There are 2-3 generations per year, 2nd generation July August, 3rd generation September October (in warm zones up to 4 generations).

Problems in the Combat

Since the beginning of the 90´s in Central Europe the life-cycle of the Horse Chestnut Leaf Miner Moth (Cameraria ohridella) has been well investigated, but yet still much stands in the way of its successful combat.

The main hindrance to a successful long-term fight is the entire missing of natural enemies. Domestic preditors are not specialised on the moth and create through it maximally a 5-7% reduction. That is unfortunately much too little. There are also, at the main breeding environment of the horse chestnut leaf miner moth, on Ohrid lake in Macedonian, no preditors that have specialised themselves on the food chain over the moth. Therefore a migration there was assumed and Asia now is named as the most probable zone of origin. This supposition could not be confirmed or excluded based on missing financial resources and the unstable political situation in many countries in that region up to now.

An innovative scientific theory has been put by Dr. Mirca Dautbasic of the University Sarajevo. This found in its investigations and references that the horse chestnut leaf miner moth comes to a fast genetic mutation and there are therefore also no natural enemies. If this theory should be confirmed, we will long have the horse chestnut leaf miner moth as our nuisance.

Combat possibilities up until now

Monitoring with subsequent chemical treatments
For monitoring, Delta-traps are used equipped with a pheromone. As soon as the first moths are caught a biotech preparation, such as Dimilin or Nomolt, should be used and spraying undertaken. These preparations are non-poisonous to humans.

Advantage: Effective impact
Disadvantage: The upperside of the leaves must be covered, what in large trees can only be achieved by means of elevated stages or with lorry mounted special spraying devices functioning from the ground.
Mass Capture
From middle April one-side glued miner moth board including a pheromone dispenser (Camerariawit) is mounted on the trunk of the chestnut tree and observed. The miner moths gather over one to two weeks at the trunk of the chestnut before flight to egglaying.

Optionally 5 to 7 days after the first larger capture on the glue board the bark can be sprayed with an insecticide (e.g. Fastac) or with a biological spray agent (Naturpyrethrum or Neemazal), using low pressure, (low pressure, therewith the small moths will not be „blown away“!) At the same time very many sex ripe moths, small males and females, will be exterminated.

Subsequently 3 - 5 miner moth boards (always equipped with a pheromone-sexual attractant) be suspended in the lower part of the crown according to the size of tree. With the captured miner moths in full abundance on the boards they can be cleaned off with a trowel and the boards newly equipped with glue (Soveurode special spray glue), and again used.

New in test is a mass capture trap developed by the firm Calantis is which intensive female catches and later small males have been achieved. For your assurance, shortly yet further extensive tests will take place. We will report about these tests.

Advantage: Mass capture with pheromone traps is absolutely biological
Disadvantages: Problems through non-treated chestnuts in the area, where the Horse Chestnut Leaf Miner Moth are unhindered and can be then responsible for wrecking further havoc.

Advantage: Effective for upto 3 years
Nachteil: Only to be done by professional companies. Furthermore there are the following unclarified questions:

• What happens with the agent evident in the leaves?
• will the agent be transferred by bees through nectar and pollen?
• Are the chestnuts contaminated?
• How does/will the tree react to the agent over the long term?

It is unimportant which procedure is to be used, we must surely be prepared for a longer „battle“ to control the Horse Chestnut Leaf Miner Moth.