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Q.  I read about a new disease affecting boxwoods.  I have quite a few boxwoods in my landscape, and I am a little worried.  What is this disease and what does it look like?

A. Unfortunately, you heard correctly.  Our cool, wet spring this year, set the stage for the development and spread of a new landscape disease - boxwood blight.  The disease has been present in other southeastern states several years, but just recently arrived in Alabama.

Boxwood blight is a fungal disease that was detected in installed landscapes across Alabama this spring.  When infected boxwoods are planted in a landscape, the pathogen can easily spread to other established boxwoods via splashing water, whether irrigation or rain.  Additionally, equipment, soil, shoes, clothing and even animals can aid in the dispersal of this disease.

boxwood blight - leaf sposts2 - jim jacobi.jpgSo, what should you look for?  Symptoms of boxwood blight include circular, tan leaf spots with darker borders.  The spots may develop a bulls-eye appearance.  Infected leaves will turn brown and rapidly drop from the plant.  The sudden defoliation and resulting leaf litter scattered around the base of the plant are important symptoms to look for, as well. 

boxwood blight - Adria Bordas, VT Institute and State University, Bugwood.org.jpg

 

 

 

Defoliated stems may produce new shoots, giving the appearance that the plants will recover, only to have another round of leaf spots and related leaf drop.  The stems develop dark brown or black thin lesions or streaks that are also unique to boxwood blight.  (Photo: Adria Bordas, VT Institute and State University, Bugwood.org)

What can you do?  There is no known cure for boxwood blight.  However, a number of steps can be taken to prevent the spread of the blight.

  • In established landscapes with healthy boxwoods, do not bring in new boxwoods.
  • For new plantings, carefully inspect plants for symptoms.
  • Use drip irrigation, rather than overhead sprinkler irrigation.
  • Improve air circulation around plants through proper pruning and plant spacing.  Avoid shearing plants.
  • Don’t compost infected leaves or other boxwood plant material.
  • Clean and sterilize pruning/shearing tools between usage to prevent the spread of the pathogen on contaminated tools.
  • If you find an infected plant, remove the entire plant and place in a plastic bag.  Also, carefully rake up and dispose of all fallen leaves.  The pathogen can live on infected leaves for up to five years. 
  • Fungicides won’t cure plants, but they can be used to protect landscape plants from the disease.  The most effective fungicides contain these active ingredients: chlorothalonil, chlorothalonil + thiophanate-methyl, and tebuconazole.
  • Use resistant boxwood cultivars.  Buxus harlandii, Buxus microphylla var. japonica ‘Green Beauty’ and Buxux sinica var. insularis ‘Nana’ are some of the cultivars with good resistance to boxwood blight.
  • Consider plants other than boxwoods like rosemary, box-leaf euonymous, sweet box in shady spots, and Japanese hollies.

While this disease is not yet widespread, we should become aware of it and be observant.  Following the steps listed above can greatly inhibit the distribution of boxwood blight throughout our Alabama landscapes.  If you suspect that one or more of your boxwoods are showing symptoms, please consult with your local extension agent.  Also, for further diagnosis, you may send pictures or samples to the Plant Diagnostic Laboratory in Birmingham, http://www.aces.edu/counties/Jefferson/plantlab/ .

Written by Bethany A. O’Rear of the Alabama Cooperative Extension System (ACES). She is housed at the C. Beaty Hanna Horticultural and Environmental Center, which is based at the Birmingham Botanical Gardens.


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