Boxwood Blight – Devastating Disease Reported in Kentucky

Boxwood blight (caused by the fungus Cylindrocladium buxicola) was confirmed in October 2014.  Plants submitted to the UK Plant Disease Diagnostic Laboratory were collected from a residential landscape in Fayette County.  Homeowners suspect that infected plants were transported from a retail garden center in Jefferson County in May 2014, but official reports of boxwood decline were delayed until October when established boxwood plants on the property began to exhibit symptoms.  Original infected plants had been destroyed soon after planting.

Symptoms

Symptoms of boxwood blight are different from some of the most commonly observed boxwood problems.  For example, stem blight, freeze damage, and drought damage result in foliage turning bright bronze or straw-colored while remaining intact.  Boxwood blight, in contrast, results in rapid defoliation of plants (Figure 1).

Figure 1 – Defoliation of the lower plant canopy is often the first obvious symptom of boxwood blight.  (Photo: Nicole Ward Gauthier, UK)

Figure 1 – Defoliation of the lower plant canopy is often the first obvious symptom of boxwood blight. (Photo: Nicole Ward Gauthier, UK)

Another distinguishing symptom of boxwood blight is black/brown stem lesions that are easily recognized after leaf drop (Figure 2).

Figure 2 – Dark stem lesions are one of the most distinguishing symptoms of boxwood blight. (Photo: Nicole Ward Gauthier, UK)

Figure 2 – Dark stem lesions are one of the most distinguishing symptoms of boxwood blight. (Photo: Nicole Ward Gauthier, UK)

Earliest symptoms include leaf spots, but these spots often go unnoticed unless a regular scouting program is in place (Figure 3).  Roots are not affected.

Figure 3 – Early symptoms of boxwood blight include leaf spots, but because leaf drop occurs soon afterward, this phase often goes unnoticed. (Photo: Nicole Ward Gauthier, UK)

Figure 3 – Early symptoms of boxwood blight include leaf spots, but because leaf drop occurs soon afterward, this phase often goes unnoticed. (Photo: Nicole Ward Gauthier, UK)

Management

Avoid unhealthy plants at all costs.  Homeowners should examine plants carefully before purchase, avoiding plants with leaf or stem lesions or an unhealthy appearance.  Growers should carefully inspect incoming plants and liners before introducing them into production areas.

Use of tolerant boxwood cultivars may also be used as a protective measure, although there are no resistant cultivars.  See Susceptibility of Commercial Boxwood Varieties to Clyindrocladium buxicola by Ganci, Benson, and Ivors for cultivar ratings.

Fungicides can suppress disease development and spread, but they do not cure this disease.  Thus, infected plants should be destroyed immediately to prevent spread.  A rigid sanitation program is recommended, including destruction of plant material and leaf debris, where fungal spores reside.  For more details regarding clean-up, see our fact sheet Landscape Sanitation (PPFS-GEN-04).  Cultural practices can help prevent conditions that are conducive for the fungal pathogen.  Space plants for air circulation and rapid drying of foliage.  Overhead irrigation should be avoided.

Surrounding healthy boxwood may be protected with fungicides such as chlorothalonil, chlorothalonil + thiophanate-methyl, tebuconazole, or fludioxonil.  See The Most Effective Products for Preventing Boxwood Blight, caused by Cylindrocladium buxicola by K. Ivors and M. Ganci for detailed fungicide recommendations.

Report suspected cases of boxwood blight immediately to your local Extension agent or specialist, or to the UK Plant Disease Diagnostic Lab.

 

By Nicole Ward Gauthier, Extension Plant Pathologist

 

 

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