Box hedge disease, commonly known as box blight or boxwood blight, is a destructive fungal infection that poses a threat to all Buxus species. If left unaddressed, it can result in significant defoliation and eventual death of the plants. Unfortunately, this disease has gained increased prominence in recent years, possibly exacerbated by climate change and the heightened propagation of affected plants in nurseries. Effectively preventing and treating box hedge disease is crucial to the preservation of ornamental boxwood plants and hedges.
What Causes Box Hedge Disease?
Box blight is triggered by two closely related fungal pathogens, namely C. pseudonaviculata and C. henricotiae, both belonging to the Calonectria genus. The fungal spores produced by these pathogens can be readily disseminated through various means, including wind, rain, spray water, contaminated pruning tools, and infected nursery stock. Once a boxwood plant becomes infected, the fungus has the potential to spread swiftly, particularly in warm (60-80°F), moist, and humid conditions.
Recognizing the Signs of Boxwood Blight
Learning to quickly identify boxwood blight is critical so you can take action before significant plant damage occurs. Some key disease symptoms to look for include:
Foliar Leaf Spots and Defoliation
Small, dark or light brown spots will develop on the leaves and lead to rapid defoliation of branches as the infection spreads. Dieback of twigs and branches also often occurs.
Stem Cankers
Sunken, dark colored cankers will appear on green stems, usually starting from points where leaves meet stems. In moist weather, salmon-orange spore tendrils may exude from the cankers.
Rapid Plant Decline
As the infection takes hold, rapid branch dieback and complete plant collapse can occur, sometimes quite suddenly, especially under warm and wet conditions favorable to the pathogen. Careful monitoring and early treatment is crucial.
Preventing Boxwood Blight Infection
Although complete prevention of box blight infection is challenging, adopting prudent preventative measures can significantly reduce the risk:
Ensure Good Air Circulation
Promote adequate air circulation by avoiding overcrowding of plants. This facilitates rapid drying and helps prevent the buildup of humidity, conditions conducive to the growth of boxwood blight fungi.
Disinfect Tools & Equipment
Thoroughly clean and disinfect all pruning tools, garden stakes, ties, and any other equipment that comes into contact with boxwood. Use solutions such as 70% alcohol, a 10% bleach solution, or commercially available plant disinfecting products.
Inspect Nursery Stock
Carefully examine new boxwood plants, particularly bareroot ones, for any signs of boxwood blight before introducing them to your garden. Responsibly dispose of any infected plants to prevent further spread.
Apply Fungicides Preventatively
As a preventative measure, apply broad-spectrum fungicides like copper soap or chlorothalonil twice a year to create a shield against fungal pathogens such as Calonectria spp. Always follow the directions provided on the product label.
If box hedge disease already has taken hold in your boxwood plants, taking timely and thorough action is imperative:
Prune Diseased Plant Parts
Immediately cut away any infected plant parts, pruning back well into the green healthy wood at least 2-4 inches below visual symptoms. Bag and securely dispose of infected debris far from boxwoods.
Rake and Remove Fall Leaf Litter
Carefully rake up all fallen boxwood leaves and debris around plants and properly dispose of offsite, as blight fungi can overwinter here. Avoid excessive wounding of plants during cleanup.
Apply Fungicides Curatively
Spray applications of targeted fungicides containing active ingredients like tebuconazole or fluxapyroxad can treat active infections by inhibiting further fungal growth. Products with some translaminar movement into leaves generally work better. Rotate between chemical modes of action to avoid resistance. Follow all label precautions and directions when spraying, as misuse can damage plants.
Evaluate Long Term Plant Viability
If more than 30% of the boxwood canopy is affected and major stem cankers are present, removal and replacement of the plant might be the most prudent option to prevent recurrence.
Conclusion
Left unchecked, box hedge disease poses a major threat to beautiful Buxus hedge plants and often necessitates replacement. But by proactively monitoring for symptoms, practicing smart cultural prevention methods, and treating infections quickly and thoroughly, boxwood blight damage can be reduced and controlled in many cases allowing plants to thrive for years to come. Reach out to your local horticultural extension office for more guidance protecting boxwood beauties from this harmful disease.
