(Question)

Hello, I have a hedge of boxwoods that have been thriving for several years now. This spring, I noticed that one section was developing yellow leaves, particularly on the sides. I assumed it needed some fertilizer treatment and so I fertilized all of my hedges (some newer and smaller ones as well) with a liquid fertilizer. Two days later I noticed that the tips of the leaves were all burned. Can the hedges be saved? How do I proceed from here to reverse the damage especially if I still do not know what the initial problem was?

(Answer)

Thanks for contacting the Toronto Master Gardeners.

The problem with your boxwoods is either due to (1) a disease known as Boxwood blight or (2) a Box-tree moth that has been identified recently in Ontario. Your description of yellowing leaves indicates that it may be the early stages of Boxwood Blight. See here

If it’s Boxwood Blight, you may be able to save the plants if the disease is in its early stages. This disease has been seen in Europe for many years–unfortunately, many gardens in the U.K. have not used Box (Buxus) for several years.

However, if you observe some leaf defoliation and/or webs, then the Box-tree moth would be a concern. Even though there are some steps that one could undertake to deal with these moths, success would depend upon how prevalent the caterpillars are. If in the early stages, one might be able to control them.

We’ve included a lot of information in this post. Unfortunately, many box shrubs are under threat with the Box-tree moth as well as Boxwood Blight. Once the cause of the yellowing or defoliation of your Buxus can be determined, it may be possible they can be effectively treated. In the meantime, you may want to consider other options to replace the Buxus. See here,

Box-tree moth:

https://www.torontomastergardeners.ca/askagardener/boxwood-hedge-being-eaten/

https://www.torontomastergardeners.ca/askagardener/what-is-eating-this-boxwood-hedge/

https://www.inaturalist.org/blog/18683-an-invasive-moth-is-recorded-in-ontario-canada-for-the-first-time-observation-of-the-week-9-9-18

https://extension.psu.edu/more-trouble-ahead-for-boxwoods

Boxwood blight:

https://horttrades.com/boxwood-blight-information-page

https://www.canr.msu.edu/news/boxwood-blight-disease-identified-in-michigan

https://www.torontomastergardeners.ca/askagardener/boxwood-blight/

https://www.extension.purdue.edu/extmedia/BP/BP-203-W.pdf