The Wisconsin Department of Agriculture, Trade and Consumer Protection recently announced the first detection of boxwood blight in Wisconsin. It was found during a routine plant inspection performed by DATCP nursery inspectors at a nursery in Kenosha County. Boxwood blight is a serious fungal disease that attacks boxwood shrubs as well as pachysandra, a shade-loving groundcover.
As stated by DATCP, “The fungus causes brown spots on the plant’s leaves. The spots enlarge until they merge and the leaves drop off. Black lesions also form on the plant’s woody stems. It thrives in warm, humid conditions. It is most often spread by moving infected plants, but may also be carried on garden tools, clothing and vehicles. Even when infected plants are removed, reproductive spores may remain in the soil for up to six years. While fungicides may help prevent the disease, they cannot cure it. Once infected, plants and leaf litter must be burned, buried at least two feet deep, or double-bagged and landfilled.”
The browning of the foliage caused by boxwood blight resembles winter burn, which becomes evident at the end of winter and beginning of spring as browning of the evergreen foliage. Damage to the plant by urinating animals can also be misdiagnosed as boxwood blight. If these symptoms are noticed after removing and replacing a boxwood in an existing planting, it is suggested to have a sample of the affected plant part analyzed at a plant diagnostic lab to determine if the culprit is boxwood blight.
DATCP advises the following control measures:
Purchase less susceptible varieties. Boxwood with small sized leaves, Buxus microphylla types, seem to offer better resistance to boxwood blight. Buxus ‘Winter Gem’ and Buxus ‘Green Gem’ are reportedly tolerant to moderately tolerant of this blight.
When buying a replacement plant for an existing boxwood or pachysandra planting, isolate it for at least one month to be sure it is free of the blight before planting with established plants.
Allow air to circulate around the plants, so space accordingly when planting.
Water plants at the soil line and avoid overhead watering.
Rake and remove plant debris around the base of the boxwood planting.
DATCP offers additional information on boxwood blight at this link: https://datcp.wi.gov/Pages/Programs_Services/BoxwoodBlight.aspx
The UW-Madison/Extension Plant Disease Diagnostic Clinic provides assistance with identifying plant diseases and suggests control methods: https://pddc.wisc.edu/. If boxwood blight is suspected, contact the PDDC or Kenosha County Extension Master Gardener Plant Health Advisors: firstname.lastname@example.org.
Master Gardeners will be staffing a booth at the Kenosha County Fair from 10 a.m. to 4 p.m. Saturday in the Open Class building of the fairgrounds. They will be available to assist with plant-related inquiries and offer advice. If you would like to discuss a plant issue with them, bring specimens, if possible, to aid in determining identification, symptoms and possible causes.
Jeanne Hilinske-Christensen is the UW-Extension interim horticulture educator for Kenosha and Racine counties. Submit plant care questions to the Master Gardeners Plant Health Advisers. Phone: 262-857-1942 or email email@example.com.