After travelling the last few months, I was surprised to see a number of juniper bonsai with brown tips. Initially I thought about leave tip blight. However, it did not look right. Searching around the web has led me to believe I have miner moths of some kind in my bonsai. Searching even deeper, I found the very well set up website http://bladmineerders.nl/, a website dedicated to giving insight in mining insects in Europe. It is clear that this species can have a big impact on all my junipers so I will have to find a way to get rid of this pest.
Symptoms of the cypress tip moth
The first thing I noticed was dead tips in the junipers. When you look more closely, you can find little holes in the tips. The dead tips are completely hollowed out. In spring and summer I should be able to find small moths (a few millimetres!) hanging out near the junipers, confirming my assessment.
(inspired by http://bladmineerders.nl/)
In late spring to summer the moths appear from their pupae. After mating, they lay eggs on the fresh shoots. During autumn the larva mines a mere 9-12 leaves – the damage is quite inconspicuous. Hibernation occurs within the mine, and during mild days feeding may continue. After hibernation the larva lives as a borer, and empties 4-6 shoots, over a length of 0.5 – 2.5 mm, just below the tip of the shoot. The damaged shoots wilt and die off. In April – May the larva emerges for pupation.
How to treat Mining Moths
It is unclear what one can do against leaf mining moths in bonsai. So far, I have been unable to find an effective treatment. Once the larvae are in the shoots, they cannot be killed using a contact poison. So the main moment to get rid of them is to break their reproductive cycle at mating & mature stages.
As a first resort, I have trimmed out all visibly affected branches. Hopefully this will reduce the number of larvae in the plant, reducing the spring population of adults. I will continue looking into treatments, and update where possible.
Please leave me a comment if you know how to control this outbreak!