Boxwood Blight: Are Your Boxwoods In Danger?

If you’re noticing spots or overall decline of your boxwoods this season, it may be Boxwood Blight. Boxwood Blight, Calonectria pseudonaviculata, is a fungal disease that has defoliated Boxwoods throughout Europe since the 1990s. It was first found in the United States in October 2011. Up until 2018 infections were scattered; however, the rainy 2018 season greatly increased the spread of the disease. It has now become more noticeable in Maryland, Virginia, and DC landscapes. According to the Virginia Department of Agriculture and Consumer Services, the DC/VA/MD area is expected to see an increase of Boxwood Blight this growing season because of the wet Spring we had this year. Our Arborists warn to keep an eye out for signs of Boxwood Blight on the susceptible species listed below.

Susceptible Species:

Susceptible Boxwood Cultivars Include: B. sempervirens ‘Suffruticosa’, B. sinica var. insularis ‘Justin Brouwers’, B. microphylla var. japonica ‘Morris Dwarf’, B. microphylla var. japonica ‘Morris Midget’, B. sempervirens ‘Jensen’, B. sempervirens ‘Marginata’, Buxus X ‘Glencoe’ (Chicagoland Green), B. sempervirens ‘American’, B sempervirens ‘Elegantissima

Other Susceptible Species: Japanese spurge, Allegheny spurge, and Sweetbox

Signs & Symptoms of Boxwood Blight:

  • Dark spots on leaves
  • Brown blotches
  • Browning of leaves
  • Early leaf drop starting on lower branches and moving up the canopy
  • Black cankers (black streaks) on the green stems
  • Branch and canopy dieback
  • Overall lack of vigor
Boxwood Blight - Defoliation
Defoliation Starting At The Bottom
Boxwood Blight - Leaf Spots
Leaf Spots
Boxwood Blight - Black Cankers
Black Cankers on Stem

Boxwood Blight is easily mistaken for other boxwood diseases, such as Volutella Blight and Macrophoma Leaf Spot. A key symptom that differentiates them, is numerous narrow black cankers on the stems of Boxwoods when infected with Boxwood Blight.

Treatment of Boxwood Blight:

Unfortunately there is no cure for Boxwood Blight which is why most Arborist suggest homeowners focus on prevention. However, depending on the severity of the infection and other factors, our Arborists may suggest using targeted fungicide treatments to manage the infection and reduce dieback. If the infection is not manageable, our Arborist may recommend removing the infected plant. Be sure not to replace the infected plant with another susceptible species/cultivar because the Boxwood Blight fungus can live in the soil for 5 to 6 years and will infect the new plant.

Prevention Of Boxwood Blight:

Keep Your Boxwoods Healthy & Well Drained: For any disease it’s important to keep the plant healthy overall in order to reduce the chance of infection and the severity of infection. Make sure to get your Boxwoods regularly pruned, fertilized, and opt for preventive treatments. Since fungi love moisture, keep your Boxwood’s soil well drained and don’t overwater.

Disinfect Pruners Between Plants: Make sure to disinfect your pruning tools between plants to reduce the chance of spreading the fungal disease. To disinfect your pruning tools, dip them in a solution of nine parts water and one part bleach for 10 seconds then allow them to air dry. Scrub them with soap and water and thoroughly dry them before putting them away.

Purchase Resistant Cultivars: If you decide to still plant boxwoods in your landscape opt for cultivars that tend to be more resistant to Boxwood Blight. B. microphylla ‘Golden Dream’, B. harlandii B. sinica var. insularis ‘Nana’, and B. microphylla var. japonica ‘Green Beauty’, are all highly resistant to the fungal disease. These cultivars may contract the disease but typically will not show many symptoms and will not be greatly affected by the fungus.

Inspect Susceptible Plants Before Taking Them Home: Inspect all susceptible plants before you bring it home from the nursery. Look for signs of Boxwood Blight, such as leaf spots and cankers. To go a step farther, only purchase boxwood plants from reputable nurseries that participate in a boxwood blight compliance agreement.

Avoid Planting Boxwoods in Shaded Areas: Shaded areas allow fungal diseases to grow and flourish. Boxwoods planted in shaded or partially shaded areas will be more prone to Boxwood Blight or other fungal diseases.

If you think your Boxwood is showing signs of Boxwood Blight give us a call at 703-573-3029 or book a consultation with one of our Arborists online.

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