Many of you noticed that your boxwoods had browning of the branches and dieback in the spring. I have written a couple of columns about this and the potential problems. Many people are just now noticing that their boxwoods haven’t greened up and there are dead spots in the plants.
I am also seeing a lot of buzz on social media regarding boxwood problems followed by a LOT of misinformation regarding the problems and treatment. Remember – you MUST identify the problem correctly before taking any corrective action.
Most of the comments suggest that the problem is boxwood blight, a disease that has been given media attention in the last few years because of its potential destructiveness. Some comments are towards the foliage-eating boxwood moth. Nobody has commented about a disease called Volutella.
Again, diagnose the correct issue before acting, particularly if you are going to use a pesticide. Many are recommending fungicides and, in most cases, it’s not going to help.
Boxwood blight is distinctly different from boxwood dieback or winter injury. With boxwood blight, symptoms include leaves wilting and turning dark bluish-green and rapid defoliation. Sometimes you will see pots on the leaves and black streaks on the stems.
Symptoms of the boxwood dieback from winter injury include dead stems and yellowish-colored leaves that remain on the stem, eventually dropping. Many of the boxwoods with winter injury dieback are still holding onto their leaves.
Volutella blight is a weak fungus and doesn’t usually kill a boxwood. It hangs around until the plants are stressed and attacks leaves and stems. It won’t affect a healthy boxwood.
Symptoms of Volutella blight can be seen in the early growing season as new growth emerges. The growth is stunted and later turns a gray-green. This growth may eventually die but can also be easily pruned out. You don’t usually see it on the entire plant, but rather a branch here or there.
In addition, the bark of the stem begins to split, and you will find blackened wood under a canker.
To get really confusing, you may find Volutella blight on boxwoods that experienced winter injury, especially if they were stressed. This fungus takes advantage of these plants and enters the stems. Therefore, you may have Volutella blight as an after-the-fact problem.
If you suspect boxwood blight, contact your local county Extension office. There are a few places in the Miami Valley where it’s been discovered but not that many. Since this disease was discovered, research has found that there are good management practices to utilize to control and prevent further spread.
If it’s Volutella or winter dieback, remove the dead material, and eventually, the boxwood dead spots fill back in. Keep in mind, however, that boxwoods store their energy in their leaves and a decreased amount of leaf surface leads to decreased photosynthesis for the plant to grow.
Therefore, patience is a must if you want to keep the plant or plants!
Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at email@example.com.