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I have a mature Mugo Pine that is looking rather haggard these days due to pine sawfly larvae chowing on it year after year. I first noticed them two summers ago. There were so many of them that I could hear them chewing whenever I was weeding around it (I didn't even know what the sound was the first few times I heard it-I thought I was going crazy!) I was able to identify them quickly enough and I had some Sevin in the garage so I used it. I normally try to avoid pesticides but the bush was seriously infested (75% covered, the other 25% eaten). Because I know Sevin kills pretty much all bugs, I put a tarp down around the bush to direct the water/pesticide runoff down the driveway into the crushed stone and not into the garden soil. I had to repeat this 4 or 5 times that first summer to get rid of them all.

Last year, I tried to catch it early, and noticed what I discovered to be the eggs on many of the lower branches. I pruned as many as I could without disfiguring the bush. Then I repeated the Sevin applications each time I found some of the disgusting little buggers munching away. It was better last year, I only had to spot treat the bush instead of hosing the whole thing down. I did the same thing as last year with the tarp too, trying to be mindful of all the beneficial bugs that may be lurking under the bush.

This year, I again found the eggs all over the bottom branches of the bush. I cut a few more off but I really can't remove any more branches at this point. Between the sawflies, the heavy snow load these that two winters, and the pruning the poor thing is suffering. I am prepared to treat w/Sevin again but am thinking there must be something else I can do.

  • can I do something to prevent the eggs from hatching besides cutting the branch off and discarding it in the trash?
  • Can I treat the soil somehow to kill the sawflies pupating there at the end of their feast?

I'd appreciate any suggestions because at this point (between this, my dead lawn, disappearing pachysandra and other problems I haven't posted yet) I'm ready to sell my house w/a fully landscaped 3/4 acre lot and get a condo. I can't keep up!

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  • Oh, BTW-they are the European pine sawfly. So disgusting.
    – Jax
    Apr 26, 2016 at 0:13

2 Answers 2

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There isn't a permanent answer I'm afraid, other than removing the Mugo pine and planting something the sawfly isn't interested in, which in the end, might be the best solution. You can use horticultural oils such as neem instead of pesticides, and other ways of managing the pest are described in the link below - but in the end, that's all you're doing, 'managing' it.

http://www.treehelp.com/european-pine-sawfly/

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  • I accepted this answer, both here and in real life. I removed the mutilated mugo this season. It was totally decimated. It was not worth the effort anymore. My hatred of pine sawflies is limitless.
    – Jax
    Nov 16, 2017 at 0:50
  • Oh dear! well...onwards and upwards, it's an opportunity to plant something else you really might like. I'm sorry about the mugo too, its a particularly nice pine but it can't be helped.
    – Bamboo
    Nov 16, 2017 at 10:13
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Have you tried sprinkling Bt (Baccillus thuringiensis) powder on the leaves? When the larva ingest the Bt on the leaves, they die in about 3-4 days.

Unfortunately I've found Bt kills most insects, and by my experience, all small aquatic invertebrates (daphnia, ostracods, etc).

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  • Hmm, I'm not sure how well a powder will stay on pine needles...is it sticky at all? Would it stick if the plant was misted first with water, and if so, would the water decrease the Bt's effectiveness?
    – Jax
    May 3, 2016 at 23:00
  • The Bt powder is as sticky as any other powder, that is, if the winds are higher, the more will blow off of the needles. However, not all powder residue will blow off, so the larvae are bound to ingest some of it. If you've ever seen dust on a dark colored table, there's only so much you can blow off, then you have to wipe the rest off.
    – Bulrush
    May 4, 2016 at 11:08

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