Strange pest on apple trees

naturewestJanuary 30, 2014

Anybody know what these are? A friend of mine has them all over his apple tree. I'm baffled. They appear to be some sort of worm encased inside of a cocoon made from the material it has mined from the tree. They are attached with webbing, and form a spiral that can be stretched straight. Hope that makes sense.

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I am not familiar with this. Send your question to Cornell tree fruit disease expert, Dr. Dave Rosenberger. Email:

    Bookmark   January 31, 2014 at 5:17PM
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mikebotann(8a SE of Seattle)

I think it's a form of scale. A dormant spray should take care of it.
Post your picture in the Orchards Forum and you should get a correct answer right away.

    Bookmark   January 31, 2014 at 5:29PM
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jean001a(Portland OR 7b)

Scale. Start by mechanically rubbing it off --if the tree is reasonable size.

If it has that many scale over entire tree, consider replacing it as it has been severely weakened.

    Bookmark   January 31, 2014 at 10:49PM
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Jean, what scale are you suspecting? I've seen and dealt with lots of scale, this is different. It's hard to tell in the pic but it appears that the critter lives inside of a tube made from the frass produced by burrowing into the stem. This cocoon forms a spiral,which makes it look like a snail at first glance. They can be pulled out of the spiral to over a half inch long. I wish I had a picture showing that but I left the branch to prevent spread. I suppose I could make another visit, but I was hoping someone could identify it easily.

Mike and Nandina, thanks for the suggestions, I will take your advice.

    Bookmark   February 1, 2014 at 8:27AM
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My guess is a twig gall. Some are induced by bacteria, but if you have found some sort of larvae in these, I'd say they were insect caused. Which one, I don't know and you should find out. .

    Bookmark   February 1, 2014 at 9:29PM
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As advised, I sent an email to the folks at Cornell and posted in the orchard forum. This is the reply I received:

"From your posted image and description it does not appear to be scale as had been suggested by previous responders. Without an intact sample I would not be able to identify the insect. I too have never seen this structure within the pest complex on apple grown in the northeast.

It appears from your description that the structure is a hibernaculum composed of fine frass and the larva within the spiral case with webbing attaching the case to twigs is likely to be associated with the lepidopteran complex. If larva are within the casing, it seems like a somewhat vulnerable location on the tree and easy prey for other hosts?

Are the apple trees from which these images were take near a forest or other diverse ecology? You could send a sample to the Insect Diagnostic Laboratory, attention of Jason J. Dombroskie, Cornell University, Dept. of Entomology,"

So there you go. I will need to revisit my friend and get a specimen to put in the mail. Unless someone figures it out beforehand. I was hoping this would be much easier!

    Bookmark   February 2, 2014 at 8:44AM
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brandon7 TN_zone(7)

I'm fairly sure it's a twig gall. I think the Cornell people will agree with Calliope once they get a sample. The picture and some of the description does not match scale.

    Bookmark   February 2, 2014 at 2:07PM
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I agree it looks like a gall similar to what I have seen growing on oak trees in the woods on the leaves and stems

    Bookmark   February 2, 2014 at 3:46PM
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It appears that your question and pictures sent to Cornell attracted someone's attention. Over my years of dealing with them I have never seen such a quick response. Hopefully your friend will save you a trip and quickly send a sample package to the address given for the Entomology Dept. And, will further track and photograph the 'whatever it is' during the spring months and document any damage to the tree.

It is the respondent's statement. "I too have never seen this structure within the pest complex on apple grown in the northeast"
that indicates scientific steps should be followed to exactly solve this mystery which may be a new problem for apple growers.

Please keep us updated.

    Bookmark   February 2, 2014 at 6:50PM
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Yay! Mystery solved. Kudos to the brains at Cornell:

' The photos appear to be of snailcase bagworm, Apterona helix. A European native, at least in NY it is in the Capital District (I have seen it in one area east of Albany on white pine but there are reports elsewhere). I have also seen it in one nursery here on Long Island. So far here it hasn't become a serious pest. IT is a strange type of moth, parthenogenic (reproduces without mating) and have many host plants including deciduous and coniferous species.

The larvae chew up bark, soil, and other matter to attach to silk, forming the snail-like cases. The larvae overwinter. You'll probably see some leaf damage where they are present. The cases can be annoying when they crawl up to overwinter attached to homes or structures.

Blasting off with a jet of water, application of a labeled residual insecticide in season (choose according to whether on a plant or a structure), or use of other product labeled for caterpillar control (Btk, others) should control them. Of course be sure a product is labeled for that particular use.

Here are some factsheets on-line:

Dan Gilrein
Extension Entomologist'

Here is a link that might be useful: Snailcase bagworms

    Bookmark   February 2, 2014 at 10:46PM
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ken_adrian Adrian MI cold Z5

having finally read the links above.. i think ... if it need be said..

that you ought to inform your county Ag extension office immediately ...

they might be very interested in this little known problem ...

if you dont want the gubment involved.. then perhaps removal and burning is the next best option ... this usually solves such type issues ....

are you in WA ?????


    Bookmark   February 6, 2014 at 7:44AM
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Thank you so much for posting the follow-up of your findings, and doing the right thing by submitting samples. Finding pests in new territory is always disconcerting.......sigh.

    Bookmark   February 6, 2014 at 8:56PM
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I sent a link to this thread to our county extension office. I should've known, because he is REALLY good, that he was already aware of this pest. He sent me the link below:

Here is a link that might be useful: Snail case bagworm

    Bookmark   February 7, 2014 at 1:46PM
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