The fight against boxwood blight
A familiar plant in Wilton gardens and yards is under attack.
The boxwood is fighting for its life against a deadly blight that was reported in landscapes and nurseries since last August and appears to be spreading.
Boxwoods are the number one woody plant sold in the U.S., ahead of azalea, holly, hydrangea, arborvitae, and many others. “In Wilton, homeowners and businesses alike appreciate the boxwood’s rich evergreen color, neat silhouettes and its deer resistance,” said Susan DiLoreto, chair of Wilton’s Conservation Commission.
While the name “boxwood” may not be familiar, they can be seen everywhere. A common variety of boxwood in Wilton is a rich green shrub with stubby leaves. Boxwoods take well to shearing and are a frequent fixture in formal gardens or along walkways.
While a number of diseases and pests threaten boxwoods — such as boxwood leafminer and mites — boxwood blight is the primary concern in the U.S. at the moment, DiLoreto said.
Boxwood blight is caused by the fungus Calonectria pseudonaviculata and was first identified in the U.S. in the fall of 2011. It has now been detected in 25 states, according to the Horticultural Research Institute (HRI), in both nursery and landscape settings.
“The summer of 2018 was unusually warm and wet, resulting in boxwood blight being reported at an alarming rate in Connecticut,” DiLoreto said.
Symptoms include dark or light brown spots or lesions on leaves. Infected leaves turn brown or straw colored followed by rapid defoliation shortly after the leaf symptoms appear, DiLoreto said.
The fungus produces spores on the undersides of infected leaves and lesions in the stem in as short a time period as one week after infection. The spores are sticky and easily adhere to people, animals, insects, tools, and boots that come into contact with them, allowing them to spread to new plants.
“Long-distance spread of the fungus is via movement of infected plant material. The fungus can survive in leaf debris or soil during winter for at least five or six years,” DiLoreto said.
She noted that diseased boxwood leaves and cankered shoots can travel via ball and burlap material, gallon containers, and even in Christmas wreaths.
Boxwood blight is fatal. Once infected, the only option is removal of the boxwood plant.
However, there are a number of measures that can be taken to prevent boxwood blight, DiLoreto said.
Property owners should be vigilant in regularly inspecting for signs of blight. The state Agricultural Extension Station recommends calling a licensed arborist or plant care professional to identify suspected boxwood blight. If the disease is caught early and properly removed from the landscape, further spread of the disease can be prevented.
Since water is important for the spread and development of boxwood blight, avoid overhead watering. Do not prune plants that are wet.
Mulch from sources that recycle yard waste should not be used. It may import the blight. Bagged bark mulch will be “clean.”
After pruning, gardening tools should be sanitized. Sanitation and disinfection are critical disease controls. A mixture of 70% ethanol or Lysol Concentrate Disinfectant at highest label rate is recommended to wipe down all tools, boots and pots. Contact time of five minutes is recommended for tools.
Consider having a licensed professional spray preventative fungicide.
Despite good cultural practices, pests and disease appear at times. Chemical control should be used only after all other methods have failed, DiLoreto said. Fungicides can be applied to healthy plants in the vicinity of infected plants to prevent infection. In using fungicides, recognize that they are still active after they are absorbed into the soil and can kill beneficial fungi that live in the soil.