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Pine trees and caterpillars - disease?

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Pine trees and caterpillars - disease?

Postby Amber » Mon Mar 07, 2005 7:21 pm

Hi,

Does anyone know exactly what makes the caterpillars web-like nest that we tend to get this time of year and why they can kill or harm pine trees, as I have heard.

I have a few on my pine trees, but they never seem to hatch and my pines seem to be ok, I dont use any pesticides in my garden.

Thanks
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Postby devil » Tue Mar 08, 2005 12:45 pm

This is a real pest, although they rarely actually kill the pine trees, unless they are already in bad shape. They are called the processionary caterpillar and are the larval stage of a moth. The hatch from eggs laid in the trees in autumn and initially build their nests. As they grow, they crawl, in mass, along the branch, eating the pine needles as they go. In Spring, they come down the tree trunk in a continuous line and along the ground (hence the name) until they find a hole in which they can pupate and pass the summer.

They are not pleasant beasts as they have fine, mildly venomous, hairs which can penetrate the skin. Many people become sensitised to the venom and suffer severe allergic reactions simply be walking under an infected tree.

The government forests are sprayed annually to keep them under control and I think there may be a regulation forcing private owners to do the same. If they don't, after a couple of years, their trees will be stripped bare each spring. A few nests one year will become hundreds after two years. Even if there is no ruling, it is also a question of human health. I know two person who are sensitised and, if they walk anywhere close to an infected tree, they become covered with blotchy red weals (and one also has asthma attacks).

My recommendation is that you call in a specialist to deal with them (may already be too late this years) and to hell with any non-use of insecticides for this pest.
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Cutting out the nest

Postby Amber » Thu Mar 10, 2005 9:16 pm

Hi, Thanks for your reply. Devil, I really dont want to use any pesticides in the garden, what do you think about cutting them out as soon as I see the nest on the trees. Would that stop them, for that year, anyway?

They thankfully dont affect me, I am often picking the the lone one up and moving it to a secure location, I cant kill anything!

One other question, are these the small moths that we tend to find in properly laid grass?
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Postby devil » Fri Mar 11, 2005 10:49 am

I'm sorry, I'm no entomologist, so I cannot say what the moths look like.

If you call a specialist to deal with them, he will not use a chemical insecticide, but a natural enzyme that, if the caterpillars eat it, will kill them. This enzyme is specific to lepidopter larvae and, as it is unlikely that there are other species present on pine trees in the late autumn, will therefore not harm other species. Of course, blanket aerial spraying can kill other butterfly/moth species that happen to be in the larval stage at the time of spraying, but you would have your trees specifically targeted.

Theoretically, you could cut off the nests (while they are still small) and burn them, but shinning up a 20 m pine and crawling along the lateral branches would not be my idea of fun. Even then, the nest inhabitants may well be out gorging themselves when you do that.

I had the same problem when we first moved into our present house, with four 15 m pines at the foot of the garden. One January day, a few years ago, Nature helped us with a strong wind and one of them was blown over to a 30° from vertical angle. I called the Forestry Department and they came along and cut it down. The following year, the same thing happened and the other three started to tilt, although not very much, but two of them, if they fell, would cause damage to property. I therefore made an application to the Forestry Department to have them removed. A delegation of three inspectors came and decided that there was a risk and they marked the trees with a number.and gave me a piece of paper allowing me to cut them down. A month or two later, the local woodcutters spent a morning removing the above-ground parts. Removing the roots, later, was much more of a problem. However, I no longer have processionary caterpillars. Before their removal, the trees had to be sprayed twice a year, but the guy who did it used an insecticide, not the enzyme. A few metres from our garden, in forest land, there was a large pine on which there were 473 nests in 1999. It was literally stripped bare of all greenery. The following year, aerial spraying here started and it was just in the catchment area. Today, it looks fine and usually has a small handful of nests, most years. This could happen to your pine if you don't take precautions. You will find the Forestry Department very helpful.
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Thanks Devil

Postby Amber » Sun Mar 13, 2005 7:50 pm

Thanks Devil,

My pines are about fourteen feet at the mo, and look pretty healthy. I will probably take your advice in the future and spray them with the natural enzyme, when they get too big. I was a great pine tree climber when I lived in Greece (when I was about 10years) but I guess those days are gone now... Do you have any numbers for a specialist that will do this treatment? and are you sure this natural enzyme will not harm birds, (and birds that feed on these caterpillars, if there are any mad enough to do so :-) and other insects and animals (dogs?)?

Thanks
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Postby devil » Mon Mar 14, 2005 11:18 am

I understand that it attacks only caterpillars of all species, but I'm no expert. It has been deemed safe for birds and mammals. I suggest you contact the Forestry Department for more details. They probably can tell you who can spray them for you.
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