There’s a new fungus in town, Clindrocladium pseudonaviculatum, that may affect your boxwoods, Japanese spurge and Himalayan sweetbox shrubs. Boxwood blight affects infected plants rapidly, but there are preventative measures that can be taken to reduce the spread of this disease.
What is the history of boxwood blight in North America?
Since the first confirmed case in the United States in 2011, boxwood blight (caused by Cylindrocladium pseudonaviculatum) has spread to 10 states and two Canadian provinces. All of the commercial boxwoods that researchers have tested are vulnerable, as well as other plants in the boxwood (Buxus) family, including pachysandra and sweet box (Sarcococca species).
How will my plants be affected?
Although this fungal disease doesn’t typically kill its host plant, it does have a serious impact on the plant’s appearance-often stripping the shrub of its leaves completely. Although the roots remain healthy, infected boxwood looks dead, thanks to its bare branches. With still no cure in sight, the home gardener’s best line of defense is prevention. As you’re buying boxwood this year, be sure to carefully inspect each plant before making a purchase, and don’t ignore the disease’s early symptoms if you spot them in your garden.
What are the Symptoms and Spread?
- The pathogen is spread by water splash or wind driven rain, and on contaminated tools, debris and animals.
- The spores are very sticky and do not generally travel far in wind currents.
- In the nursery, rain splash moves spores from the soil on to lower foliage of the plants. The first symptoms are small, circular leaf spots that are purplish-brown in color and may show zonation. Over time, the spots coalesce and 100% of the foliage can become blighted.
- All of the lower leaves will drop on severely infected nursery stock and tufts of green growth will only be present at the end of branches.
- Stem cankers are also very common and large amounts of white fungal mycelium will be present on the foliage.
- The disease cannot be identified by visual symptoms because there are other pathogens of boxwoods with similar symptoms.
Is There a Control for Boxwood Blight?
- The fungicides that were recommended to control the pathogen are not currently registered in Canada for use on nursery stock. Further work is necessary to identify the most effective fungicides and to expand their registration to boxwoods.
What are the Best Practices Used for Controlling the Spread of Boxwood Blight?
- At Higher Ground Gardens, we are disinfecting all pruning tools using Lysol between each job site we visit.
- If you plan on adding boxwood, pachysandra or sweet box plants to your garden this year, be sure to inspect plants before bringing them home from the nursery.
- It is also recommended that you avoid introducing new boxwoods to established boxwood plantings that are doing well in your garden.
The Canada Nursery and Landscape Association is continually updating the horticulture industry on the spread of this disease. We will also keep you up to date with any new information we receive.
This article was written using information from the articles by Kelly Ivors, associate professor and extension specialist in the Department of Plant Pathology at North Carolina State University as well as North Carolina State University Cooperative Extension, the Canadian Landscape and Nursery Association, and Fine Gardening.com