Boxwood Blight
While most news continues to be bad, there is some good news in the fight against this devastating disease. As with all fungal diseases, boxwood blight is almost impossible to eradicate once in plants or soil; it can survive for five years or more. It was first noticed in Europe in the 1990s and eventually made its way across the Atlantic to begin devastating boxwood collections in North America. According to Purdue University’s College of Agriculture.
Boxwood Blight is a disease caused by the fungus Cylindrocladium buxicola. The disease has been prevalent in Europe for over 20 years, and made its way to the United States in 2011. First found in North Carolina, it has since spread along the east coast and continues to move across the states each year. Fungicides may prevent infections in uninfected plants. However, spraying already blighted plants is not only ineffective but expensive and harmful to the environment.
Common, and particularly English boxwood (Buxus sempervirens and B. sempervirens ‘Suffruiticosa’), are especially susceptible to boxwood blight. Some varieties, which are known to be more tolerant than others, are being studied, propagated, and hybridized. NewGenTM, a hybrid Buxus, will be introduced in the nursery trade in 2020. For established collections, do everything you can to prevent fungal spores from coming in contact with your plantings. While not wind-borne, sticky spores may move short distances in the air. Spores can come in on contaminated boxwood or other susceptible plants (pachysandra, sweet box), as well as infected holiday boxwood greenery. Pruning tools, spray hoses, clothing, shoes, and wildlife also spread the disease.
Boxwood Blight’s most characteristic symptoms include brown/black, circular leaf spots that lead to defoliation, as well as dark black streaks on the stems of the infected plant. It is a sticky pathogen that moves through splashing water, plant to plant contact, equipment, or in debris. The optimal conditions for this pathogen include damp areas with little air movement between around 70-75 F (21-23 C). Unfortunately this pathogen can survive for long periods of time in plant debris. There is no known cure at the moment, but there are lots of tips on prevention and management.
Boxwood Leafminer
Boxwood Leafminer (Monarthropalpus flavus) is one of the most destructive boxwood insect pests. First found in 1910, they can now be found anywhere boxwood grow in the United States. The eggs of this fly are laid inside the leaf where the larvae develop and feed on the tissue. This feeding results in blotchy, blistered leaves that swell, discolor, and can prematurely defoliate. The small, orange, mosquito-like fly emerge in late April or early May (in Virginia) and spend about 2 week mating and laying eggs. The larvae are the most destructive to the boxwood plant and they can feed from June through the early fall. It’s been reported in 20 US states, three Canadian provinces, throughout most of Europe, New Zealand, and the Republic of Georgia.
NEW BUXUS CULTIVARS
Cultivar: Buxus NewGen Freedom® ‘SB300’ Zone: 5-8
Growth Rate: Fast, 3 to 6 inches per year Sun Exposure: Sun, part sun, shade
NewGen Freedom® is a relatively vigorous, rounded cultivar that is slightly taller than wide. It has beautiful glossy medium green foliage. Its habit is more uniform and tighter than ‘Wintergreen’ or ‘Winter Gem’ thus making it an excellent choice for many formal and residential landscapes. Deer resistant! NewGen Freedom® should be pruned each year in late winter to early spring. If not pruned, the plant will tend to open up in the center, especially in spring when new foliage is wet and young. NewGen Freedom® is very resistant to boxwood leafminer and very tolerant of boxwood blight. It has very few disease or pest issues when planted and cared for properly. NewGen Freedom® is an excellent boxwood. It was selected due to its high tolerance of boxwood blight and resistance to boxwood leafminer. Its vigor helps it create an attractive plant quicker than many cultivars but it also makes annual pruning a must. With annual pruning, this plant makes a fabulous specimen.
Uses: Medium specimen, medium hedge, foundation plant
Substitutes: ‘Wintergreen,’ ‘Winter Gem,’ ‘Jim Stauffer,’ ‘Green Mountain’
Size: 15 years (3.5’ Tall and 3.5’ Wide) 25 years (5’ Tall and 5’ Wide)
Cultivar: Buxus NewGen Independence® ‘SB108’ PP28888 Zone: 5b-8 with continued testing underway
Growth Rate: Medium, 2 to 4 inches per year Exposure: sun, part sun, shade
NewGen Independence® is a very deep green medium sized cultivar that holds excellent color throughout the winter. It has a rounded habit that is nearly as tall as wide. NewGen Independence® can be used in formal plantings where a medium sized round plant is desired. Would be a replacement for Buxus sempervirens ‘Suffruticosa’ (English Boxwood) for foundational plantings. Branching structure is very strong allowing it to withstand most moderate to heavy snow loads. Deer resistant. NewGen Independence® should be pruned lightly in late winter to early spring to maintain uniform shape. It is not uncommon for fall frosts to burn new growth that occurred in the late summer or fall. These burned shoots can be removed in late fall after first freeze or in late winter/early spring depending on the gardener’s preference.
More information about Boxwood Blight can found in the Summer 2019 Issue of GCA’s The Real Dirt