Shrubs turning black
Some of my shrubs have bark turning black and some limbs are dying. What is the cause and how can I treat them?
Clackamas County Oregon
Thank you for your questions. Before we can proceed, I have a few for you:
1. What are the names of the shrubs?
2. If you don’t know their names, can you send me pictures of the shrub when you reply to this email? The best pictures are at least 3 views:
(a) the entire shrub and its surroundings;
(b) the shrub by itself;
(c) a single branch (against a plain background) which shows the leaves as well as the blackening.
If you cannot send images, perhaps a friend, neighbor, or relative might be able to help you.
3.If it’s impossible to send images, please take a sample of an affected branch (one that still has some leaves) to the Clackamas County Master Gardener office where you will receive first-hand help. The office is at 200 Warner-Milne Road, Oregon City, 97045. Phone 503-655-8631. Hours weekdays 9 to noon and 1 to 4; closed holidays.
I look forward to receiving your pictures.
Hi! Attached are pics. Two of a pieris and the last of a maple (the maple was just pruned and so there's not much black showing). Affected shrubs are a rhody, pieris, and abelia and are close together and probably 20 years old. The maple is young and twenty feet away from the shrubs. My guess is the shrubs have some kind of blight. The maple looks different in that the whole branch died, but there's no black anywhere else on the tree - yet.
Thank you for sending the images.
It's difficult to determine what is occurring with the pieris. The white may be lichens (normal and unimportant) or fungus. If fungus, the underlying wood is dead. Thus, the only remedy would be to remove the dead stems.
So, here’s how you might proceed: (1) Take a sample of an affected pieris branch to the Clackamas County Master Gardener office for a first-hand estimate as to the problem before (2) you contact several Certified Arborists to request an onsite evaluation and recommendation. You can locate nearby Certified Arborists by using your zip code at https://www.treesaregood.org/
The diagnosis for the coral bark maple is a bit easier to determine from your image. Coral bark maples are marginally adapted to our climate and can be damaged by episodes of lower than usual temperatures during the cold months. The blackening is the result of a bacterial infection (Pseudomonas species) which often follows non-lethal damage from low temperatures.
The remedy is to remove all the blackened tissue. Because this is a bacterial infection, the removal is best done during dry weather. Destroy the removed wood.