Boxwoods turning brown - Ask Extension
My boxwoods are developing brown patches on them; on some it’s just random twigs but on others there are whole sections of the bush that have died o...
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Boxwoods turning brown #850263
Asked September 17, 2023, 6:21 PM EDT
My boxwoods are developing brown patches on them; on some it’s just random twigs but on others there are whole sections of the bush that have died off. I don’t see evidence of insects, but I’m not sure what to look for (or even if I should be looking for insects). What may be causing this, and what can I do to stop it? Thanks.
Warren County Ohio
Expert Response
Hi Jon,
Your problem is of interest to me because your boxwood photos show the same damage as the ones in our Cuyahoga County yard. However, our problem developed over the winter and was evident in spring, while your description appears to state they "are developing" now at the end of summer, so I doubt your problem is winter damage as was reported for boxwood in our area. That appears to be something remedied by pruning out the dead wood.
Nor does you problem appear to be boxwood leafminer. The evidence of leafminers is illustrated in the linked articles: https://bygl.osu.edu/index.php/node/1768 and https://bygl.osu.edu/index.php/node/1461. Their damage is not evident in your pictures and any such damage would be expected in the spring.
Boxwood Blight, an emerging serious problem, has been reported in Greater Cincinnati, comparatively next door to Warren County, in the linked article: https://bygl.osu.edu/index.php/node/1359. The article notes that boxwood blight may, but not always, be evidenced by leaf spots or discolorations, or by stem blackening. I could not tell whether they were on your plants. It also notes:
"Research has also shown that boxwood blight can be prevented through season-long fungicidal applications made at around 14-day intervals. However, no fungicides have been found that offer a curative option; the disease cannot be halted in plants that are infected. This means that while fungicides may be used as part of a boxwood blight management plan, they should not be the only tool in the management toolbox." [emphasis added]
The article notes protective strategies for uninfected plants. It is important to know that boxwood blight is easily confused with the similar but less devastating and more common Volutella Blight, as described in the article. Therefore, I suggest you send a sample for testing. OSU's Wayne Ellett Plant and Pest Diagnostic Clinic, https://ppdc.osu.edu/, performs such tests.
I wish I had a more definitive diagnosis of something easy to treat.
Thank you for your question.
Your problem is of interest to me because your boxwood photos show the same damage as the ones in our Cuyahoga County yard. However, our problem developed over the winter and was evident in spring, while your description appears to state they "are developing" now at the end of summer, so I doubt your problem is winter damage as was reported for boxwood in our area. That appears to be something remedied by pruning out the dead wood.
Nor does you problem appear to be boxwood leafminer. The evidence of leafminers is illustrated in the linked articles: https://bygl.osu.edu/index.php/node/1768 and https://bygl.osu.edu/index.php/node/1461. Their damage is not evident in your pictures and any such damage would be expected in the spring.
Boxwood Blight, an emerging serious problem, has been reported in Greater Cincinnati, comparatively next door to Warren County, in the linked article: https://bygl.osu.edu/index.php/node/1359. The article notes that boxwood blight may, but not always, be evidenced by leaf spots or discolorations, or by stem blackening. I could not tell whether they were on your plants. It also notes:
"Research has also shown that boxwood blight can be prevented through season-long fungicidal applications made at around 14-day intervals. However, no fungicides have been found that offer a curative option; the disease cannot be halted in plants that are infected. This means that while fungicides may be used as part of a boxwood blight management plan, they should not be the only tool in the management toolbox." [emphasis added]
The article notes protective strategies for uninfected plants. It is important to know that boxwood blight is easily confused with the similar but less devastating and more common Volutella Blight, as described in the article. Therefore, I suggest you send a sample for testing. OSU's Wayne Ellett Plant and Pest Diagnostic Clinic, https://ppdc.osu.edu/, performs such tests.
I wish I had a more definitive diagnosis of something easy to treat.
Thank you for your question.
Greg, thanks for the information! This gives me several possibilities to consider and to check out. I appreciate it!
