Boxwood Blight Continues to Persist

Boxwood Blight, caused by the fungus Calonectria pseudonaviculata, seeped into the Midwest a few years ago and continues to persist despite measures to control the disease. But before your dig up and burn all your browning boxwood shrubs, be sure you have correctly diagnosed. Boxwood are after all notorious for being afflicted by winter desiccation and drought.

IDENTIFYING BOXWOOD BLIGHT SYMPTOMS

Brown spots on leaves, commonly displaying as circular with a dark brown edge
Spots quickly enlarge and merge together
Rapid defoliation, within weeks or even days
Black streaks on stems and twigs
If there is any doubt get a professional diagnosis

When purchasing any Boxwood be sure to inspect plants for possible symptoms and only purchase from nurseries that adhere to the Boxwood Blight Cleanliness Program. Any new Boxwood plant purchase should be isolated for several weeks before planting as symptoms may take that long to appear. A fungicide may have depressed the symptoms temporarily.

PREVENTING BOXWOOD BLIGHT

Spores of the Boxwood blight fungus can be spread with your pruning tools, your gardening clothing and gloves, or any other equipment you may be using while tending your gardens. This fungus does not travel well by air, so introduction to your landscape and gardens will typically take place by noted contact and infected plant material, including boxwood limbs used for Christmas decor. Also be aware that other species of the boxwood family can harbor the fungus. These should also be monitored for symptoms.

Avoid these cultivars of Boxwood listed in order of highly susceptible to moderately susceptible:

‘Suffruticosa’
‘Justin Brouwers’
‘Morris Dwarf’
‘Morris Midget’
‘Jensen’
‘Marginata’
‘Glenco’ Chicagoland Green
‘American’
‘Elegantissima’
‘Green Mound’
‘Conroe’ Gordo
‘Green Pillow’
‘Grace Hendrick Phillips’
‘Jim Stauffer’
‘Green Mountain’

Choose these cultivars of Boxwood listed in order of most resistant to moderately resistant but be be aware that they may still carry the disease undetected:

‘Golden Dream’ ***
harlandii ***
‘Nana’ ***
‘Green Beauty’ ***
‘Eseles’ Wedding Ring **
‘Winter Gem’ **
‘Katerberg’ North Star **
‘Sprinter’ **
‘Franklin’s Gem’ **
‘Dee Runk’ **
‘Fastigiata’ **
‘Green Gem’ **
‘John Baldwin’ **

Also monitor these species that can host the fungus:

Japanese Spurge
Allegheny spurge (Pachysandra)

To help minimize the chances of this fungus from infecting your new or existing plantings:

Choose the most resistant varieties available to you for new purchases
Choose open habit varieties (Buxus microphyllo) rather than the tightly compacted (Buxus sempervirens) to improve air circulation
Plantings should be well spaced so that they do not overlap at maturity
Plant in full sun
Water plantings with a soaker hose to keep foliage as dry as possible
Mulch boxwood plantings to prevent soil splash that could contain the fungus
Tend boxwood plants only as absolutely necessary, minimizing the contact with infected tools or gloves etc. Ideally prune when dormant.
Sanitize your tools and equipment after contacting each Boxwood plant. One part bleach to nine parts water can be used to sanitize.

TREATING BOXWOOD BLIGHT

This aggressive fungus really cannot be effectively controlled once plants are infected and the soil may harbor the fungus for as long as 5 or 6 years. Remove all infected plant materials. Do NOT compost any infected debris. Double bag it and send to the landfill or burn it. Sanitize all tools, shoes, gloves etc to prevent the spread to anything susceptible still in your gardens or landscape.

If replacing plantings with resistant cultivars it is advised to select the ***most resistant cultivars. **Moderately resistant cultivars may require fungicide treatments as will any other boxwood thus far not infected. These treatments are costly and will be required for the life of your plants. Fungicide applications need to be repeated every 7 to 14 days through every growing season. Typically this would not be undertaken other than by professionals for large plantings or highly valued specimens. Treating with prescribed fungicide will not eradicate this disease, but will only keep it controlled at best/

BOXWOOD ALTERNATIVES

Certain Boxwood cultivars will harbor the fungus but not be affected by it and show no symptoms. These partially resistant or tolerant varieties should be selected for your gardens, or consider other species.

Hinoki Cypress
Ilex glaubra an evergreen Inkberry with habit similar to Boxwood
Ilex crenata an evergreen Japanese Holly
Japanese False Cypress
Juniper
Ligustrum spp Privest is especially good for hedges
x Pyracomeles Juke Box evergreen with glossy leaves can give a similar appearance and shape to Boxwood
Thuja occidentalis American arbovitae are evergreen with similar shape to Boxwood but with much different leaf structure
Vaccinium Blueberry Glaze forms a compact mound of dark green foliage for hedges. Fall produces purple foliage and fruits
Yew
Or simply abandon your vision of Boxwood or hedging and consider something of loose colorful form or flowering shrubs.

Boxwood shrubs have been very popular in our home landscapes. Hopefully if you have them they are resistant, and if you intend to plant any just be sure to select carefully.