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Plant Diseases/Ash Tree Bark Damaga



Earlier I shared with you about an 5 and a half inch caliper autumn blaze maple that an insect, most likely borer, damaged a 2 x 3 inch area under the bark. The tree is trying to heal itself growing bark from both the left and right sides to cover the hole.

You recommended spraying the tree trunk and the wound with Merit 75WP. I finally found a bottle of that online that's 2 oz in size.

My question is this. How much of this powder to I add to a gallon of water to spray with a tank sprayer the trunk and wound area?

I read the entire fine print label and only got a headache.

Thanks for your help!



ANSWER: Labels can be confusing at times. The recommendation is about 1 teaspoon per inch of diameter in a gal of water. Since you will not need this much mixture to spray this 5 inch tree I would put 2.5 teaspoons in a 1/2 gal of water and spray at  a low pressure until the mixture runs down the trunk. I would wait about ten days and repeat. This should be enough insecticide to kill any borer under the bark. I hope this helps.

---------- FOLLOW-UP ----------

Trunk of Purple Autum Ash
Trunk of Purple Autum  

Trunk of Purple Autum Ash closer view
Trunk of Purple Autum  

Thanks for mixing amounts for Merit 75WP!

I have a Purple Autumn Ash tree that had three nail like round holes in the trunk in 2011. The holes were level with each other and spaced about an inch apart.

By July of 2012 they looked what you see pictures in the two attached photos. I had a local tree service visit. He said the holes are not borers but sap suckers and there is nothing that can be done.

Unfortunately, I can't take a picture of the trunk today because my camera died yesterday. Today, the holes are completely grown over and there is an outward bulge in the area where you see the damaged in the attached photos.

Yesterday I also noticed many vertical cracks in the outer layer of the bark all along the main tree trunk. Its like some cut the bark with a knife and the bark edges separated.

They remind me of the cracks that happen to thin skinned young maple trees in spring during the freeze thaw cycle, but there are many cracks on the ash.

The tree is full of leaves.

Is this borer damage or whats going on?

Many Thanks Jim!


I think that is sap sucker damage and it looks like the tree is growing over the damage. The vertical cracks sounds like just normal growth--as maples and ash grow older the bark will change form smoother to more rough and that is what this sounds like. I would not worry about that. If you are concerned you can spray a little of the Merit mixture on the holes and it will not harm the growth just keep insects away.

Next spring, I would fertilize both tree with 10-10-10 fertilizer at the rate of 1 lb. per inch of trunk diameter scattered around the tree and watered in good. Apply just before a rain event and you will not need to water. Apply just as the new leaves are budding out and the roots will carry it to the trunk and foliage and this will  increase the overall health of the tree.  

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Jim Hyland


30 years experiance in the ID and management of forest diseases and ID of landscape tree diseases.

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