Introduction of boxwood blight

Nicole Ward Gauthier/UK

Early symptom of boxwood blight include the development of circular leaf spots with dark borders.

Boxwood blight can be devastating to American boxwood cultivars, which are common in the Kentucky landscape. Complete defoliation can occur within a week and plants can die within a single growing season. Use of tolerant cultivars, cultural practices, and fungicides can reduce incidence and spread of boxwood blight.

Boxwood Blight Facts:

Symptoms on leaves can appear as light or dark brown circular leaf spots with darker borders (see photo). These symptoms often go unobserved due to rapid defoliation. Defoliation of the lower plant canopy is often the first obvious symptom of boxwood blight.

Dark brown or black streak-like lesions appear on infected stems.

Favored by warm, humid weather.

Caused by the fungus Cylindrocladium buxicola.

The pathogen can survive on plant debris in the soil for at least 6 years.

The disease may be spread by splashing water, wind, tools, clothing, and wet hands. Long distance movement is reliant upon the transport of infected plants, infested soil, or contaminated equipment.

Avoid Introduction of Diseased Plants:

Careful selection of healthy plant material is the first step to prevent spread.

Inspect nursery plants carefully; do not purchase unhealthy or symptomatic plant material.

Discuss concerns with landscape contractors before new landscapes are installed.

Cautiously Introduce New Plants into Established Landscapes:

Protect established landscapes, especially if valuable boxwood are on site.

Introduce only symptom-free plants into landscapes.

If valuable or established boxwood already exist, avoid hasty introduction of new boxwood plants. Move new plants in slowly by setting up a transitional site or quarantined area that can serve as a holding area for three weeks. If plants remain vigorous and symptom-free, they are likely safe to introduce to landscapes.

Management Options:

If boxwood blight is confirmed, the following management options are recommended:

Diseased boxwoods in landscapes should be removed immediately to prevent spread.

Replant landscapes with boxwoods that have disease tolerance.

Diseased boxwoods grown for commercial sale should be destroyed and not sold.

Once boxwood blight has been diagnosed in the landscape follow these steps to prevent infections to nearby healthy boxwoods:

Increase plant spacing and prune dense shrubs/trees within the landscape to allow for air movement, reduced humidity, and rapid leaf drying.

Minimize overhead watering and sources of leaf wetness that can increase fungal spore production.

Fungicides do not cure boxwood blight. Use of fungicides can help protect nearby healthy plants, but residual protection lasts only 7 to 14 days. Homeowners can utilize fungicides containing chlorothalonil to protect plants from infection or suppress disease development. Always follow label directions when utilizing fungicides.

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