Arborvitae 'Emerald Green' and Bag Worm

mombay(6)April 12, 2010

I have recently planted 90+ Arborvitae trees. I understand they are succeptible to bag worm. I don't see

any bags on them now however I understand they should be sprayed. Could you advise when they should be sprayed and with what chemical? Also, how often should they be sprayed?

Thanks very much in advance for your help.


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gardener365(5b Illinois USA)

Hi Nancy,

BTK is a biological insecticide that can be sprayed when you notice any bagworms present. Until you do, don't spray them.


    Bookmark   April 13, 2010 at 7:46AM
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ken_adrian Adrian MI cold Z5

i do NOT suggest proactive spraying of chemicals or organics on a preventative basis ...

i have at least 100.. and have never seen a bagworm on any of them ...

why dont you wait until you have at least seen one.. and then spray that one ... and go on from there ....

contact your county Ag office for guidance on whether this is an actual threat in your county ....

good luck

    Bookmark   April 13, 2010 at 8:31AM
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dcsteg(5 Shawnee, KS.)

Here in Kansas City if you see 1 there is a 101 right around the corner. Best to catch them in their infant stage...1/4 inch or less. Usually late May or June around here when they make their appearance.

If you have 90+ trees and detect them call a professional to spray all them. Cost prohibitive to do it yourself.


    Bookmark   April 13, 2010 at 9:13AM
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ken_adrian Adrian MI cold Z5

hey dave

are you saying she should do prevention..

or are you saying that when she sees one.. then she goes nuclear ...


    Bookmark   April 13, 2010 at 12:57PM
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dcsteg(5 Shawnee, KS.)

Hey Ken...You can't do prevention. There is no exact day or time when they appear. Late May or early June here. Can and does vary depending where you live. Best to let them get established, 1/4 inch or so, to feed then spray.

Not a hard critter to control but you need to catch them in time or they will destroy a small conifer overnight. This almost happened to me on 1 of my 4 ft. Picea p.'Blue Totem's. There were 100's on it overnight and when I looked at it the next day needles were drying up and falling. I saved it but recovery was slow and it has not caught up with the other 2 in the grouping. Large specimen conifers damage is minimal but worthy of treating. Some of the bags left on the trees over Winter are female and contain next years crop of critters if not treated.


    Bookmark   April 13, 2010 at 4:46PM
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We planted about 10 home depot emerald green arborvitae, and we didn't pay attention and almost lost 2. We picked the bags clean but I am waiting until I see some of the smallest larvae wriggling around before I will hose them with BT, and if necessary more.

But with 90, that would be a lot of work just to even check them, but better to hit hard once than keep trying to get them gone over time.

If you see a bag, take a few and put them in a plastic zip-lock bag, and observe them; when the wrigglers come out of there, you will know to spray the rest of your trees as well.

    Bookmark   May 16, 2010 at 10:56PM
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We have about 100 thuja green giant, and they do get bag worms in Dallas TX (in clay soil, dry, hot). Treat with bifenthrin insecticide or the bag worms can kill entire trees. Significant brown damage even when caught under 1/2 cm size. Spray around May 1, no later than June, if you had problems the prior year. Will have to use a systemic such as Imidicloprid soon since they are about 15' tall and cannot spray much higher. That worked via spray; not sure if it will if watered in via the roots. Bifenthrin works great if you can get to them (100% dead next day). Home Depot type products not near as effective, particularly once they get big. Worth obtaining bifenthrin if you have bag worms!

    Bookmark   June 9, 2010 at 3:20PM
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So far, bag worms have not become a problem this far north. I think it would break my heart if climate change were to allow these things to invade our native "cedar" stands up here. 'Tis one of my very favorite plants, especially in its wild tree form, like my woods is full of. That would be my last straw I'm afraid. There are advantages to living in such a cold place.

Of course, none of this addresses your problem, mombay. I would take the advice to find out first if this insect is a problem in your area. Then and only then would I come up with a treatment plan.


    Bookmark   June 9, 2010 at 8:01PM
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