Boxwood: When Have You Had Enough?

Specialty cut flower growers often use filler or background plant material to accent their flower displays. During the winter many people use the evergreen foliage of boxwood. The plants lend themselves to frequent cutting with good recouping ability during the growing season. The foliage is deep green, adding to the beauty of several styles of arrangements.

The problem is that all is not well in the boxwood world.

A nasty foliar disease imported from Europe is now rampaging through boxwood nurseries, as well as plantings in landscapes and cut flower operations. The Latin name is Cylindrocladium buxicola. Once a plant is infested it defoliates, and dies very rapidly. The fungus also infects the stems, resulting in distinctive and diagnostic dark brown to black lesions, sometimes with an angular, diamond-like pattern. Black lesions can be found along a stem, from the soil line to the shoot tips. Unfortunately, this disease is easily spread from plant to plant.

Making Lemonade from Lemons

Lately I have been searching for good uses for dead boxwoods. I found that owing to its fine grain it makes an excellent wood for carving. Wood carvers tell me they cannot get enough good boxwood of useable diameter. The boxwood is also resistant to splitting and chipping. It has been used for years to make decorative boxes and hair combs, as well as carved chess pieces.

Boxwood was once called dudgeon, and was used for the handles of dirks and daggers. Boxwood was a common material for the manufacture of flutes and recorders in the eighteenth century, and a large number of mid- to high-end instruments made today are produced from one or other species of boxwood. Even bagpipes used to have chanters made from boxwood.

What is Going Down?

If you are a woody cut stem grower struggling with keeping boxwood alive you may be pondering “Why did I plant those #$%@ boxwoods in the first place?” Last fall’s warm, humid weather on the East Coast resulted in a mega infection period, resulting in massive boxwood leaf drop in October. We were flooded with calls and emails about boxwood blight for about a three-week period. It was not until the temperatures fell into the 30F range that the leaf drop stopped.

Karen Rane and David Clement visited a site in Maryland where the manager had religiously applied fungicides on a weekly basis the whole summer into the fall, and his boxwoods looked pretty good. This worked but is this what an IPM approach is about? If you have to spray something regularly just to keep it alive it begs the question “Is this really worth it?”

Boxwood blight is here and it will rear its ugly head again next season. The long-range solution is to find the genes that enable boxwood to resist this disease and work them into a new line of resistant plants. This is years off in the future. Meanwhile, you should really look at whether boxwood is such a good idea.

As If That Wasn’t Bad Enough

Not to throw fuel onto an already flaring fire but we also have a new bug entering the picture.

In Europe it’s called the boxwood tree moth, but in the U.S. people are calling it boxwood moth. Its Latin name is Cydalima perspectalis, and it is in the family Crambidae. It is from Asia (Japan, China, Taiwan, Korea, and Russian Far East) and showed up in Germany in 2006, then appeared in Switzerland and the Netherlands in 2007. It was found in Great Britain and France in 2008, and in 2012, it was introduced from Italy to Sochi with the planting stock of Buxus sempervirens. This little, actually pretty moth, is working across the European community rapidly. The moth has not made a splash in the Americas, but several specimens were found in Ontario, Canada in late August of 2018. It’s just a short matter of time until it shows up in the United States.

The larvae feed on the leaves and shoots of Buxus species. The young larvae eat only the upper part of the leaf. The leaves are not destroyed completely but appear as “peeled” or shredded almost completely, and eventually die. Older larvae are the most damaging: they massively and completely eat the leaves, sometimes leaving a thin part at the contour and center of the leaf. Green, ball-shaped frass (caterpillar poop) can usually be seen on host plants.

Every plant has at least one or two disease and insect pests; boxwood just seems to be really good at accumulating a plethora of problems. It might be wise to explore other plants that do not give you heartburn.

Stanton Gill

Extension Specialist in Nursery and Greenhouse IPM

Stanton Gill is Extension Specialist in Nursery and Greenhouse IPM, Central Maryland Research and Education Center, University of Maryland Extension and Professor with the Landscape technology Program, Montgomery College. Contact him at [email protected]