Emerald Green Arborvitae Issues - Ask Extension
My two-month-old plated trees started to show brown leaves more and more, and some leaves turned black. I installed a drip irrigation system and have...
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Emerald Green Arborvitae Issues #876065
Asked July 05, 2024, 10:57 PM EDT
My two-month-old plated trees started to show brown leaves more and more, and some leaves turned black. I installed a drip irrigation system and have a humidity meter, so trying to do my best to keep them healthy and alive. Today, I inspected all of them, and on almost all, I found white, almost fine powder-like spots and when I touched it a small white insect flew you can see the insect in image 4868. On many of the trees I also see this brown sap, see in image 4864. On a single tree, I found this bulge on the trunk; I thought it may be bagworms, but I am not sure. Could you please advise why they are oozing the brown sap and whether the white moths like be an infestation and what to use for treatment? Many thanks!
Prince George's County Maryland
Expert Response
My two-month-old plated trees started to show brown leaves more and more, and some leaves turned black. I installed a drip irrigation system and have a humidity meter, so trying to do my best to keep them healthy and alive. Today, I inspected all of them, and on almost all, I found white, almost fine powder-like spots and when I touched it a small white insect flew you can see the insect in image 4868. On many of the trees I also see this brown sap, see in image 4864. On a single tree, I found this bulge on the trunk; I thought it may be bagworms, but I am not sure. Could you please advise why they are oozing the brown sap and whether the white moths like be an infestation and what to use for treatment? Many thanks!
Given that your trees have been in the ground for only two months, they are very new and still establishing. They will need to be closely monitored for water needs for the whole 18-24 months of establishment.
Browning can be a sign of drought/heat stress, which would be understandable given our recent very high temperatures and lack of rain. Drip irrigation can be useful, but you will need to physically monitor the root areas of your trees to be sure they are getting what they need. To do this you will probe first with a screwdriver or dowel, (under mulch), and then feel with your finger. The soil several inches down should feel cool and moist after watering.
Here is our watering information:
https://extension.umd.edu/resource/watering-trees-and-shrubs/
The trees should have mulch (keeps soil cool and moist) around the base *no deeper than 2-3 inches, kept pulled back from the trunks.
The white insect looks like a planthopper nymph, which are not of concern, and the brown bulge in the third photo is an old praying mantis egg case, which isn't hurting anything.
We can't tell what is causing the sap flow in your second photo but it could be from bark injury, a borer insect or a canker infection, which can be brought about by drought stress.
The most common reason a new tree struggles is not due to insect pests or diseases but to environmental stressors like poor planting/placement or aftercare of watering.
Overall if you think the trees don't look well, you can attach a photo or two to this reply and we'll be happy to take a look.
Christine
Browning can be a sign of drought/heat stress, which would be understandable given our recent very high temperatures and lack of rain. Drip irrigation can be useful, but you will need to physically monitor the root areas of your trees to be sure they are getting what they need. To do this you will probe first with a screwdriver or dowel, (under mulch), and then feel with your finger. The soil several inches down should feel cool and moist after watering.
Here is our watering information:
https://extension.umd.edu/resource/watering-trees-and-shrubs/
The trees should have mulch (keeps soil cool and moist) around the base *no deeper than 2-3 inches, kept pulled back from the trunks.
The white insect looks like a planthopper nymph, which are not of concern, and the brown bulge in the third photo is an old praying mantis egg case, which isn't hurting anything.
We can't tell what is causing the sap flow in your second photo but it could be from bark injury, a borer insect or a canker infection, which can be brought about by drought stress.
The most common reason a new tree struggles is not due to insect pests or diseases but to environmental stressors like poor planting/placement or aftercare of watering.
Overall if you think the trees don't look well, you can attach a photo or two to this reply and we'll be happy to take a look.
Christine
Thank you so much, Christine! It is great to hear that the moths are not threatening. I think you are right about the weather being not very helpful this season for the little trees.
The sap is concerning to me; here is what I found on Google:
"As soon as an insect penetrates the bark of an evergreen, the tree pitches out. It squirts globs of sticky sap, and the sap engulfs the insect."
I believe I saw something in one of the sap puddles, too. Do you think it would be good for me to spray the trees to keep insects away? Do you have any recommendations for treatment?
Thank you for sending me the watering article, it was very helpful.
Best,
Mari Hello Mari,
We do not recommend treatment in this situation, and there are no sprays that can be applied to the exterior of the plant that will eliminate any stem-boring insects that might already be inside the wood. Plus, chemicals that can discourage them from entering the trunk in the first place tend to be more risky to beneficial insects (the insecticides can't target only these pests).
Borers often take advantage of plants under stress -- like from drought or under-watering -- so the key factor to discouraging those insects from attacking the plant in the first place is to keep the plants minimally-stressed by watering as needed based on weather and monitoring the soil moisture levels. Oozing sap (gummosis) can result from borers, infection, injury, as well as general stress, so its presence alone can be hard to diagnose between those four possibilities.
Miri
We do not recommend treatment in this situation, and there are no sprays that can be applied to the exterior of the plant that will eliminate any stem-boring insects that might already be inside the wood. Plus, chemicals that can discourage them from entering the trunk in the first place tend to be more risky to beneficial insects (the insecticides can't target only these pests).
Borers often take advantage of plants under stress -- like from drought or under-watering -- so the key factor to discouraging those insects from attacking the plant in the first place is to keep the plants minimally-stressed by watering as needed based on weather and monitoring the soil moisture levels. Oozing sap (gummosis) can result from borers, infection, injury, as well as general stress, so its presence alone can be hard to diagnose between those four possibilities.
Miri
Thank you so very much Miri, this is very helpful and I will keep an eye on them regularly and see if there are other changes. Thank you again!
Best,
Mari You're welcome!
