I have about a dozen century-old boxwoods (mostly English,some Americans [and...
I have about a dozen century-old boxwoods (mostly English,some Americans [and i know that is not the proper terminology], about 6' tall. Over the past several years there has been significant dieback. Leaves on a branch turn pale green, then brown, and gradually fall off. At first I thought it was the result of the battering they tok from the heavy snows a couple of years ago, but the problem has persisted and spread. Now I think it may be boxwood blight. I would appreciate your advice. These are wonderful old plants, and probably quite valuable. The boxwoods grow in good soil with sun until mid-afternoon. The dieback seems to move back from the outer twigs, but it can appear randomly over the plant. If it is blight, is there any hope? I am pruning the dead branches and have recently cleaned the ground below the plants as well as I could. I read recently of tests in North Carolina of fungicides that showed promising results for Spectro90WDG. Might that help? If so, should I have them sprayed now or wait until Spring?
Montgomery County Maryland
It is almost impossible for your boxwoods to have boxwood blight. The infection would have had to come in on new boxwood and, unless you have introduced some questionable boxwoods lately, yours are safe from boxwood blight. In addition, boxwood blight causes extensive leaf drop from the bottom up, which is not the symptoms you are seeing. This is our website's page for invasive diseases: http://extension.umd.edu/hgic/invasives/invasive-diseases Click on the Boxwood blight for more information.
If you replace any of these boxwoods with new plants, we recommend that you start the new plants from cuttings from your plants. That way, you are guaranteed not to introduce the disease into your landscape--because once it gets in, it is extremely difficult to control.
What your boxwoods are struggling with is most likely volutella, a fungal disease. it causes patches of dieback, and the leaves turn the light tan shade in your photo. You will need to prune out all the dead areas and then, to prevent the problem in the future, thin out the boxwood foliage so that the foliage does not stay wet for extended periods which is the situation this fungus likes. The foliage can get too thick on boxwoods, and because of the humidity in Maryland, boxwoods must get good air circulation in order to avoid fungal problems like volutella. There may also be some fungal leaf spot, too, but the most important problem is the volutella.
See the following fact sheet from our website for diagnosis and, by scrolling down the page, you'll see specific information on boxwood volutella (and other fungal problems.) http://extension.umd.edu/learn/ipm-series-boxwood-hg52
Here is some more info from our website: http://extension.umd.edu/learn/volutella-blight-boxwood