Boxwood is a popular evergreen shrub that is widely planted in residential and commercial landscapes. It’s generally free of pests and diseases and has been cultivated in this country since the eighteenth century, having been introduced from Europe by British colonists. A few years ago however, boxwood blight showed up in the United Kingdom and has since spread to other European countries, devastating boxwood forests and plantings. It was inevitable that it’d show up in the United states, and in 2011 it was discovered in North Carolina. It has slowly spread north and westward. There is no known cure, unfortunately, and it will eventually show up in the Midwest.
Gardeners in Central Indiana have been alarmed by what they think are symptoms of boxwood blight on their boxwoods, but fortunately, they are mistaken. Distinctive yellowish ringspots on the leaves are the work of boxwood leafminers, a pest whose maggots feed within the leaves and causes the leaf to blister where these blotch-like leaf mines are located. If left untreated, the boxwoods will die.
Luckily, infested boxwoods are easily cleansed of leafminers with a systemic insecticide applied in spring. The active ingredient in the insecticide is harmful to bees, so wait to treat until after the boxwood blooms in April. There are many inexpensive systemic insecticides on the market at garden centers and big box stores, and they are very easy to use. One treatment lasts for months which is long enough to eliminate all the leafminers.
Remember that weakened or stressed plants are more susceptible to pests and diseases than those kept vigorous and healthy by annual fertilizing and adequate watering during dry spells.
Happy gardening!