It’s been called America’s favorite shrub, and for good reason. It has an elegant appearance and works well as a foundation planting as well as a hedge. It is adaptable to a wide range of growing conditions and is simple to maintain. Because it grows slowly, it can be used in containers or as a topiary. Its small, rounded leaves remain evergreen throughout the year.
Unfortunately, it is susceptible to the disease boxwood blight. And it’s lethal.
Boxwood blight (Calonectria pseudonaviculata) was first identified in the UK in the 1990s. It was discovered in New Zealand in 2002 and on the east coast of the United States in 2011, and it is now found in approximately 20 states.
The pathogen attacks boxwood (Buxus) species but can also be found on pachysandra and sweet box (Sarcococca). It has no effect on those plants, but it can spread to boxwood.
Boxwood leaf drop is another name for boxwood blight. It could be mistaken for winter damage, dog urine damage, drought damage, or other boxwood foliage diseases.
It has become a major issue for buxus growers, and it is now invading our landscapes. When we bring diseased boxwoods into our gardens, it spreads.
There is no need to be concerned if boxwood blight has not yet been detected in your state. Knowing the signs and symptoms of this disease will help you be better prepared if it occurs in your area.
Boxwood blight is a fungal disease that thrives in wet and humid environments with temperatures ranging from 60 to 80°F. When temperatures rise above 84°F, the disease is suppressed.
Conidia, or fungal spores, are spread by splashing water on our tools and clothing and on the fur of animals. The life cycle of boxwood blight can be completed in just one week. Within 5 hours, the infection can occur. The symptoms appear after approximately 7 days. Spores can survive for three weeks without a host plant.
Pachysandra and sweet box are two other hosts. These plants are not killed by the disease, but they can help it spread.
Identification and Damage
It is critical to correctly and quickly identify this disease. It is occasionally confused with winter damage, dog urine damage, or volutella leaf blight.
Boxwood blight is a reportable disease in many states, so contact your county extension service if you suspect it. They will instruct you on how to submit samples for testing.
There are three strong identifiers that tell you it’s boxwood blight:
- Leaf spots that are brown or tan with a brown or purple edge. Sometimes there is a purple halo around the spot.
- Black cankers on the stems. If a canker grows big enough, it can encircle the stem and kill it.
- Rapid defoliation, especially on the lower leaves.
This disease spreads from the roots to the top of the plant. Leaf drop can occur within a matter of days.
When the leaves begin to fall, the shrub weakens and may die within a few months. This disease can quickly spread through your Buxus hedge, usually through splashing water (even from a light rain), and you could lose the entire hedge within a growing season.
Preventing Boxwood Blight
This disease is brought into the garden. It does not travel on the wind and is not vectored by insects, so it does not simply “appear.” It frequently enters on a new, infected plant and spreads to other plants via rain, watering, people, and animals. It can even be found in boxwood branch wreaths, garland, and greens for the holidays.
Before planting new boxwoods in your landscape, quarantine them for at least 30 days. If you see signs of blight, get them out of your garden as soon as possible! Boxwood-containing holiday decorations should be avoided.
You may have heard that there are resistant varieties, but they are only tolerant, not resistant. They can be infected even if they do not show symptoms, and the disease can spread to other, more susceptible Buxus in your garden.
The spores are extremely sticky, and they will adhere to your clothing, shoes, and tools. They will also adhere to animal fur. This has the potential to spread the spores to other shrubs.
Maintain good garden hygiene. When it’s raining, the foliage is wet, or it’s very humid, don’t prune. Rake up all clippings and dispose of them (do not compost), wash your clothes and gloves, and clean your shoes. Clean your tools.
A new 2-inch layer of mulch can cover any infected, fallen leaves you missed. This can prevent spores from landing on healthy plants.
Control of Boxwood Blight
There is no cure for an infected shrub. Once a diagnosis has been made, remove the infected plant as soon as possible. This will aid in reducing their spread throughout your garden, especially if you have a large number of them.
Dig up the diseased plant, clean up any fallen leaves and stems, and wrap everything in plastic to prevent spores from spreading. It is recommended that you dispose of your waste by burying it (2 feet deep), burning it (if permitted), or throwing it away. Always avoid composting diseased plants or plant parts.
Boxwood blight can live in the soil for up to 5 years, so avoid planting boxwood near diseased plants.
The best way to control boxwood blight is to keep it out of your garden in the first place.
When purchasing boxwood, inquire whether the grower is a member of the Boxwood Blight Cleanliness Program. If the answer is no, or if the salesperson is unsure, go somewhere else. Landscapers in several parts of the United States will only use Buxus in designs if the homeowner insists; some nurseries no longer guarantee boxwood, and some no longer sell it at all.
The first line of defense against any insect or disease problem is always scouting. Inspect your plants frequently, especially when the conditions are favorable for disease spread. During these times, avoid performing maintenance tasks that could aid in the spread of the disease, such as pruning, shearing, and weeding.
Boxwood blight cannot be cured by fungicides or homemade remedies.
If this disease has been detected in your area, fungicides can be used as a preventative on healthy, uninfected plants. For information on diagnosis and treatment, contact your county extension service or the state department of agriculture.
If you live close to a botanic garden, arboretum, or state university, they may have a plant clinic that can help you. If you decide to implement a fungicide program, you should consider hiring a professional.
Alternatives to Boxwood
Should you plant Buxus in your yard? Many of us have spent a lot of money on boxwood for foundation plantings and garden borders. There is no reason to remove your hedges or begin a fungicide treatment program if boxwood blight has not been detected in your area.
Proceed with caution if you need to replace a plant in your hedge! Follow the guidelines outlined above.
If you’re looking for new plantings for your landscape and think boxwood might be the answer, it’s worth looking into some alternatives. Here are a few of our favorites. Your garden center or a local landscape designer can assist you in identifying other options that would be ideal for your garden.
- Inkberry Holly (Ilex glabra) is hardy in USDA zones 3 to 9, and grows 3 to 10 feet tall depending on the cultivar. This plant requires a moist, acidic soil and likes full sun to part shade.
- Japanese Holly (Ilex crenata) is hardy in zones 5 to 8, and slowly grows between 4 to 8 feet tall. You need both male and female plants if you want berries. Grow in full sun to part shade, in a slightly acidic, well drained soil.
- Pyracomeles (Pyracomeles) is hardy in zones 7 to 9 and grows 1 to 3 feet tall. It is similar in texture to Japanese Holly. It can be grown in full sun to part shade, and needs well-draining soil.
- Globe arborvitae (Thuja occidentalis) is hardy in zones 3 to 7. It can reach a mature height between 2 and 10 feet depending on the cultivar. Grow in full sun to part shade in moist, well-drained soil.
- Yews (Taxus) are hardy in zones 4 to 8. Cultivar sizes range from 2 to 20 feet tall! They grow best in full sun to part sun and need a very well-drained soil.