Boxwoods

Asked April 23, 2019, 4:14 PM EDT

My boxwoods have brown leaves on the outer extremities this spring. Beyond a few patches at the surface, the rest of the plant looks healthy. They have not yet done the usual spring leaf growth. Fungus among us or frostbite from the cold winter? Is it a good idea to apply preventive fungal treatment? What treatment is recommended for that current boxwood fungus outbreak?

Washtenaw County Michigan

3 Responses

Hello,

Several things can match your description. If you can attach a picture of the

whole shrub, and a clear close up of a short section with a few leaves, that may help narrow it down. Also peel open a leaf and look for tiny larvae inside.

Here is a reference on boxwood issues-

http://extension.umd.edu/sites/extension.umd.edu/files/_images/programs/hgic/Publications/HG52_IPM_Boxwood.pdf

If damage is from winter burn then clip these off, bag and discard. This year’s growth will soon fill the shrubs in.

The fungus to which you refer is boxwood blight. It has been found in Michigan, and it can come in on live Christmas decorations that use boxwood. If you suspect that is what your shrubs have, contact MSU Plant Diagnostic clinic to confirm it. https://www.canr.msu.edu/news/have-a-closer-look-at-your-boxwood-wreaths-this-holiday-season

This article from Wisconsin has preventative fungicides that can be used on healthy shrubs. Note that you must use more than one fungicide, rotating them through the season. Diseased shrubs should be removed, sealed in bags or buried( once you have verified blight is the problem).

https://pddc.wisc.edu/2019/02/04/boxwood-blight/

I will watch for your pictures. Thanks for using our service.

Here are some pictures. No larva inside leaves. Reading the reference you provided and looking at the pictures leads me to believe winter damage -- but I've had these for 10+ years and never had so much winter damage to deep into the bush (usually just minimal damage on new fall growth).

Yes, I agree it is winter damage. The outer growth may have been too new to survive the winter, or the shrubs went into winter too dry. Be sure you water up to a hard frost, or the ground freezes; and don’t prune in late summer or fall so late growth isn’t encouraged. Sometimes, winter is just too cold!