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Arborvitae Black Spots ID? Pics!

Posted by ocelaris (My Page) on
Sun, Apr 24, 11 at 11:35

Hi, we planted 7 Emerald Green Arborvitae in the back to shield to give a little privacy and the trees are doing generally all right but I have this black decaying foliage that I can't figure out what it's from?

I had worked the dirt incorporating peat and they are watered on drip irrigation throughout the hot summer, but not too much as I know they don't like it too wet. They're thrived despite having bag worms (which I have picked off mostly) in the past year, and sprayed with BT. I tried copper fungicide once, but that hasn't seemed to stop the black areas of dying foliage.

I've researched it for a while and everybody mentions animals using the trees as litter boxes, but there's only cats around, and no way could they pee up that high...

Hopefully someone can reccomend a fungicide or similar if that's the cause? I have Daconil/Chlorothalonil for my roses, which is what I use because it's too close to the veggies to use anything else.

Thanks, Bill

Here is a link that might be useful: Pictures of Arborvitae disease

Follow-Up Postings:

RE: Arborvitae Black Spots ID? Pics!

RE: Arborvitae Black Spots ID? Pics!

IMHO ... skip the chemicals...

just trace back and prune out the offending foliage.. they will fill back in ... sterilize the pruners between plants ...

someone will tell you what it is specifically ... i cant recall if its a mildew or a fungus ...

but all i do.. is pruning ...

if they have been there a few years.. i would salvage the weep hose.. and leave them to free range ... they are not a foo foo plant that will need watering for the rest of their lives.. it looks like you have plenty of other garden projects to use the water on ...

they look too healthy for you to spend too much time worrying about them ...


RE: Arborvitae Black Spots ID? Pics!

Ok thanks, I'll turn the water off to them, it's just another loop. Yes, my space as you can see is very limited here in NYC, so every inch counts! I will cut off the diseased parts, I was just worried about it spreading, or being a reinfestation from the bag worms last year. I think I got all of the bags, but I will have to see this year.

Here's the yard after some more work

RE: Arborvitae Black Spots ID? Pics!

"I think I got all of the bags, but I will have to see this year".

You never get all the just think you do.

One missed one means infestation.

Spray mid June to July depending on when they hatch in your area. Wait till they are 1/4 inch long and then hit them.


RE: Arborvitae Black Spots ID? Pics!

Thanks, I'll give that a shot. I wasn't sure exactly when to spray, I had the bags in a plastic bag, and was waiting for them to "emerge" so I'd be spot on. But of course the bag always blew away, and gave up on that. So that will help to know to start in june and/or when their size is about 1/4".

RE: Arborvitae Black Spots ID? Pics!

That damage is caused from dog or cat urine. It is quite common to see it on Thuja. It is not a fungal disease.

RE: Arborvitae Black Spots ID? Pics!

I have read that before, but these are up against a fence. There are feral cats but no possibility of dogs coming anywhere near. I'm pretty sure there is cat feces back behind there. Is it fertilizer burn from the feces? Because there are patches 2 feet up that no cat could have physically peed on...

Should I cut out the black spots and let it regrow? Let's just say the feral cats and I aren't on good terms, they make a mess everywhere in my back yard...


RE: Arborvitae Black Spots ID? Pics!

I have planted sixteen of these plants. I planted eights last fall and eight this spring. The eight I had planted in the fall or doing well have grown nearly two feet. But, six of the remaining eight that I planted late this sping appear to have the same problem your plants do. One is nearly dead with only a few twigs remaining. I pulled the brown/black damage off of the remaining plants and they seem to be doing better. There is new growth on the plants.

I thought that I might have underwatered them. The eight plants that are doing well get a great deal of east light. The other eight which are not doing well get east and west light. From what I see, the plants with the most west light are doing worse. \

I have pulled and cut the brown/back spot from the trees and increased the watering. Two of the trees do seem to be doing a litle better.

As far as pet urine and feces goes, I see little animal feces in my yard. And the damage is mostly in the upper parts of the trees and it seems to impact some limbs more than others. I suppose animals could be urinating on the lower limbs and as the limbs die, the upper part of the brances die first.

I'm curious about what you discover.

RE: Arborvitae Black Spots ID? Pics!

I would guestimate that (fungus) is formed from wet conditions whether man-made or heat-created from excess water/humidity at the soil surface, including splashing of soil onto foliage.

Usually this type of blackening is at the bottom of the plant. I'd prune it out and then spray with a mild fungicide such as liquid Copper (once or twice - follow the label but once right away after cuts and then a follow up after four weeks). Do follow the above posters instructions about cleaning your blade with rubbing alcohol between all cuts.


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