damaged shrubs #744421 - Ask Extension

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damaged shrubs #744421

Asked April 15, 2021, 8:21 AM EDT

I planted what I thought were boxwoods 30 years ago. In the last 3 or so years, several of the shrubs had sections go brown and die. I thought they had boxwood blight because the damage looked like the pictures I found on Google. I had my lawn care company arborist visit yesterday and he said those shrubs were NOT boxwoods but Japanese Holly and that was not blight but insect damage and too much water in the roots. I signed up for their 8 application ($50 each) shrub treatment program but now I'm not sure if it's worth it if I can't treat them myself. Do you have an arborist who can visit my property to give me another opinion on what's affecting my shrubs?

Henrico County Virginia

Expert Response

Thank you for contacting the Henrico Extension Office.  Unfortunately, we do not do site visits for homeowner diagnostics.  We are able to help with diagnosis of plant problems using the resources of labs at Virginia Tech through submission of pictures and when COVID restrictions are lifted, through physical samples brought to our office.

With the identification of the plant as a Japanese holly and the description of how the plant is dying, I believe the problem to most likely be Black Root Rot.  Any insects would be secondary to the Black Root Rot.  

I've attached our publication on Black Root Rot of Japanese Holly. Our guidance is that any plants that are showing die back, should be removed.  You could do preventative treatments on remaining plants with a fungicide (listed in publication).  And also being careful to not move any contaminated soil from the dead/dying plant to other plantings.  Taking precautions to sanitize tools and equipment too.  The recommendation would also be to not replant any Japanese holly plants back in that location.  

To confirm the diagnosis of Black Root rot, remove some of the fine roots on the damaged plant size and see if you see black roots as shown in the second publication attached.  If unsure, you could submit close up pictures of the roots here for me to look at.
Ed Olsen Replied April 15, 2021, 1:32 PM EDT
Thanks a lot for your response and useful information.  Of course, I'm disappointed that I can't save my shrubs. My lawn service guy said that the roots may have too much water but he thought that, if I cut them down to about 2 feet, that they'd come back.  He kept emphasizing insects as another cause so he wanted to treat them with chemicals 8 times a year at $50 per treatment.  I declined.

Re: the water issue, the problem started when I put a deep layer of mulch around them several years ago.  Could that have caused the root rot?  Also, the plants are only in the sun in the morning.

In case you'd like to see my plants, I've attached some pictures below.

Thanks again. 

On Thu, Apr 15, 2021 at 1:32 PM Ask Extension <askextension@eduworks.com> wrote:
Robert Boyle Replied April 16, 2021, 10:10 AM EDT
Thanks for the pictures, that does look like the typical Black Root Rot symptoms.

I'm not sure that adding a deep layer of mulch caused the moisture problem.  It could have added to it.  3-4" is not too deep.  I am seeing a downspout in the image, so if that is not diverted away, then most likely it is that along with the excessive rains in 2018 and 2020.  


Ed Olsen Replied April 16, 2021, 10:15 AM EDT
Actually, you’re likely right about the downspouts. There are  four of them draining into my shrubs!

On Fri, Apr 16, 2021 at 10:15 AM Ask Extension <askextension@eduworks.com> wrote:
Robert Boyle Replied April 16, 2021, 10:27 AM EDT

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