Showdown in the Boxwood Hoophouse

A row of infected boxwoods in Connecticut.
Photo courtesy of  University of Maryland Extension.

An invasive plant disease just rode into town. There is going to be a confrontation, and I hope the good guys win, because if we don’t, boxwood could be in trouble. Here is the story:

Boxwood blight (Cylindrocladium pseudonaviculatum) was discovered in England in the early 1990s, causing a blight on Buxus species. An outbreak of the disease occurred in 1998, and the disease is now considered widespread in Europe. Boxwood blight severely impacts the appearance of boxwood. These shrubs are normally evergreen, but the disease causes the leaves to turn brown and fall off.

In October 2011, boxwood blight was reported infecting plants in two nurseries in North Carolina. Nearly simultaneous outbreaks were also reported in Connecticut and Virginia. After these initial finds, the United State Department ofAgriculture (USDA) requested several states conduct trace-out investigations to determine if the disease had spread elsewhere. In response to this request, the Oregon Department of Agriculture (ODA) surveyed 12 nurseries named in the trace-out investigations. Other states also participated in this effort. As a result, boxwood blight was reported in an six additional states. This disease has also been found in British Columbia.

ODA has expanded our survey and discovered diseased plants at two of 24 nurseries. We’re working with the positive nurseries on eradication.

In the much of the country, boxwood is an important ornamental hedge. It is less common in the Pacific Northwest, but you see them around. Good examples of boxwood hedges can be found on the grounds of Oregon’s Capitol.

Oregon is a huge boxwood producer. About 200 nurseries grow many different varieties; most are sold out-of-state. Boxwood is among the most popular shrubs produced here. One of Oregon nurseries we’ve been working with has more than 15 acres in boxwood production!

Thankfully, this plant disease is not as serious a risk as another recent invader, sudden oak death. There are no native boxwoods, and the disease is not a threat to native habitats. For Oregon, the biggest challenge will be to keep it out of our nursery industry. ODA is working with Oregon State University (OSU) and the Oregon Association ofNurseries (OAN) to spread the word on preventive measures and best management practices.

Homeowners with boxwood hedges or specimen plants will also need to pay attention. This disease doesn't spread through the air. The spores are sticky. Spread is from plant to plant via rain wash or contaminated hedge trimmers. Gardeners with valuable boxwood hedges should be careful to buy healthy nursery stock from reputable dealers. They should also sanitize hedge trimmers frequently, and trim less thrifty plants last.

Boxwood blight likes warm, wet conditions. If you have a valuable boxwood plant/hedge and you notice it is suddenly loosing leaves, get it checked out. Put a sprig with the symptoms in a plastic bag and take it to the OSU plant clinic or ODA lab.

We have a chance to turn back this invasion, but we’re going to have to act fast because the blighter snuck in before we even knew he existed. Now that we’re aware of the sneaky nuisance, our best strategy is to snuff him out whenever we encounter him and take precautions so he’s got no place to settle. Nurseries and homeowners are going to have to be vigilant. If we work together, we can run him out of our nurseries and protect our beautiful green hedges. Let’s do it.

Dan Hilburn