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How to Box out Boxwood Blight

In 2011, boxwood blight (Calonectria pseudonaviculata; formerly: Cylindrocladium buxicola) was identified in the U.S., causing defoliation of boxwood species. It has resurfaced in some areas of the country this year and best management practices are needed to prevent the onset of the disease

Figure 1 Boxwood blight.
Mary Ann Hansen, Virginia Tech, bugwood.org

Boxwood blight thrives in warm and humid environments and causes symptoms such as tan leaf spots with dark borders, dark brown-black streaks and cankers on infected stems and ultimately severe defoliation. The fungus enters the plant through the leaf cuticle or stomata and survives as mycelia in plant debris. When conditions are favorable, white spores are produced on the undersides of leaves and on infected stems; continuing the spread of disease to neighboring boxwood. This disease can sometimes be mistaken for Volutella blight, another common and serious disease of boxwood. Under humid conditions, this pathogen produces salmon, pink fruiting bodies on infected stems.

Prevention Tips

The first line of defense to boxwood blight is strict sanitation practices and disease scouting so that any infections can be found early and removed from the production area immediately. Other helpful steps include:

  • Training your staff to recognize symptoms
  • Inspecting new plants upon delivery
  • Keeping stock separated from existing plants
  • Practicing good sanitation to mitigate risks
  • Applying fungicides preventively
  • Getting an accurate diagnosis quickly if you notice anything unhealthy
Fungicide Recommendations

Fungicides are best utilized in a disease prevention strategy to help protect uninfected plants. For control of boxwood blight and other diseases affecting Boxwood, alternate or tank-mix products from different mode of action groups to form a good resistance management strategy.

FRAC Group  
Use Rate (per 100 gal)  
7 + 11
4-7 oz.
Daconil Ultrex®
22 oz.
Daconil Weatherstik®  
22 fl. oz.
Medallion® WDG
4 oz.
Concert® II
M5 + 322-35 fl.oz.
9 + 12
4-6 fl. oz.

​​​​​​​Syngenta offers several fungicides that have been proven effective at preventing Boxwood Blight. Learn more about our solutions for boxwood blight by visiting www.GreenCastOnline.com/Ornamentals.


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