How to treat brown boxwoods - Ask Extension
Can you help me diagnose and treat my brown boxwoods ?
Knowledgebase
How to treat brown boxwoods #868031
Asked May 11, 2024, 7:08 PM EDT
Can you help me diagnose and treat my brown boxwoods ?
Howard County Maryland
Expert Response
I wanted to add additional information.
There are 5 boxwoods in my garden. They were all planted at the same time, 8 years ago. This is the first year that I've seen any brown leaves on them. Only 2 of the 5 seem to be affected. I have more photos of the damage, but I could only upload 3.
After I took these photos, I scraped back the layer of mulch so I could add new garden soil on the top, mix it in with the existing soil and replace the mulch. When I did that, I noticed that there was a lot of white stuff under the layer of mulch that I scraped off. Could it be mold?
Thanks in advance for your help,
Kathy
Hello Kathy,
If you would like to share more photos (close-ups of not-fully-dead-yet foliage would be helpful, and any white soil residue you mentioned), you should be able to send them with any reply. Or, they can be pasted directly into the body of your reply as well.
It's hard to determine from the photos exactly what is causing the damage, but you can explore our boxwood diagnostic page for symptoms that seem to match. Our prime suspect for branch browning like this is Volutella Blight (not to be confused with Boxwood Blight, which we do not suspect), a very common fungal disease of stressed boxwoods. The foliage also looks like it has heavy Boxwood Mite feeding damage.
If mold is on the soil surface or growing on aging mulch, that is usually harmless and can be ignored. For the future, we don't recommend disturbing the root zone of boxwood since they are fairly shallow-rooted and sensitive to root injury. Mixing-in additional soil or compost should not be needed for established plants, though applying a very light (an inch at most) layer of compost on top of the soil, below any mulch, can help improve drainage in clay-heavy soils over time. (Soil life like worms and insects will "till" it in for you without stressing roots.) Boxwood also appreciates a pretty light mulching, such as only around an inch, to avoid depriving roots of too much rain percolation and to help maintain soil oxygen levels.
Different boxwood cultivars have different degrees of vulnerability to the various pests/diseases common to this shrub, so that might be playing a role in their susceptibility, in addition to how often or how extensively they are pruned. (Boxwoods are best with minimal pruning, and not sheared, because that promotes dense outer growth that is more prone to infection.)
The shrubs with heavy damage (at least a third of the shrub is dead or dying) are best replaced, but if you wanted to try rehabilitating them, you could cut them back drastically to force regrowth. If the issues are only above-ground problems (Volutella doesn't kill roots), and if the root system is healthy enough and not weakened (such as by last year's drought, or over-watering/poor drainage), the plant may regrow well and regain a more normal appearance. A photo example of a renewal-pruned boxwood which is starting to regrow is attached.
Miri
If you would like to share more photos (close-ups of not-fully-dead-yet foliage would be helpful, and any white soil residue you mentioned), you should be able to send them with any reply. Or, they can be pasted directly into the body of your reply as well.
It's hard to determine from the photos exactly what is causing the damage, but you can explore our boxwood diagnostic page for symptoms that seem to match. Our prime suspect for branch browning like this is Volutella Blight (not to be confused with Boxwood Blight, which we do not suspect), a very common fungal disease of stressed boxwoods. The foliage also looks like it has heavy Boxwood Mite feeding damage.
If mold is on the soil surface or growing on aging mulch, that is usually harmless and can be ignored. For the future, we don't recommend disturbing the root zone of boxwood since they are fairly shallow-rooted and sensitive to root injury. Mixing-in additional soil or compost should not be needed for established plants, though applying a very light (an inch at most) layer of compost on top of the soil, below any mulch, can help improve drainage in clay-heavy soils over time. (Soil life like worms and insects will "till" it in for you without stressing roots.) Boxwood also appreciates a pretty light mulching, such as only around an inch, to avoid depriving roots of too much rain percolation and to help maintain soil oxygen levels.
Different boxwood cultivars have different degrees of vulnerability to the various pests/diseases common to this shrub, so that might be playing a role in their susceptibility, in addition to how often or how extensively they are pruned. (Boxwoods are best with minimal pruning, and not sheared, because that promotes dense outer growth that is more prone to infection.)
The shrubs with heavy damage (at least a third of the shrub is dead or dying) are best replaced, but if you wanted to try rehabilitating them, you could cut them back drastically to force regrowth. If the issues are only above-ground problems (Volutella doesn't kill roots), and if the root system is healthy enough and not weakened (such as by last year's drought, or over-watering/poor drainage), the plant may regrow well and regain a more normal appearance. A photo example of a renewal-pruned boxwood which is starting to regrow is attached.
Miri
