Boxwood (Buxus) species are popular landscape and garden shrubs. They have been important plants in many well-known gardens across the nation. Recently, a severe blight known as Boxwood blight (Cylindrocladium buxicola), was identified in 2011 in the U.S. causing defoliation of Boxwood species. This disease thrives in warm and humid environments causing symptoms such as leaf spots, cankers, straw/bronze colored foliage and defoliation. The fungus enters the plant through the leaf cuticle or stomata. It survives in the environment as mycelia in plant debris, and when conditions are favorable, spores are produced spreading the disease to neighboring boxwoods. There are no known resistant boxwood species, although differences in susceptibility can vary with the cultivar. In addition to Buxus spp., Pachysandra terminalis was identified as a new host of this disease in 2012.

The first line of defense to Boxwood blight begins is strict sanitation practices and plant disease scouting so that any infections can be found early and removed from the production area immediately. There has been limited research in the U.S. on this disease but there are products that have shown good efficacy on Cylindrocladium species. In 2012, trials conducted by Dr. Kelly Ivors at North Carolina State University showed that fungicides from FRAC codes M5, 9, 11, & 12 applied on a 14 day interval effectively protected plants from Cylindrocladium buxicola.

Evaluation of Fungicides for Prevention of Boxwood Blight

2012 - Ivors, N.C. State

Treatments applied three times on a 14 day interval

Fungicides are best utilized in a plant disease prevention strategy to help protect uninfected plants. Alternate or tank-mix products from different mode of action groups to form a good resistance management strategy. Evaluate treatments for plant safety on a small group of plants or cultivars before widespread use, especially if surfactants are included in the mix.

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