One of the most popular plants in the Midwest is, without a doubt, the beloved Boxwood. Homeowners are generally big fans of Boxwoods—and for good reason. They’re an incredibly hardy and compact plant that can perform well in a large variety of landscapes.
While Boxwoods are so appreciated for being easy, that’s not to say that they’re 100-percent foolproof. Like other plants, things can go wrong. If your boxwood is turning brown in its center or your boxwood leaves are turning yellow—or it’s experiencing some other problem—then you might be trying to figure out what to do. After all, you’re not a plant expert, nor should you have to be, and you’re really not sure what to do next.
The photos below represent 4 of the most common issues that Boxwoods in our area are incurring.
Box Tree Moth
Below are more, in depth, information on these Boxwood afflictions.
This pest is the most serious pest of this evergreen plant. It occurs everywhere in the USA from the East to the West coast. All varieties of boxwood are susceptible but the slower-growing English varieties are less susceptible than the American cultivars. The leafminer feeds between the upper and lower sides of the leaf.
Symptoms and Diagnosis
The larvae feeding between the upper and lower parts of the leaf causes blisters on the underside of the leaf. The leaves infested by this pest become yellow and smaller than a normal leaf. When the plant is severely infested, it appears completely unhealthy.
Boxwood leafminers over-winter as partially-grown larvae in the leaf blisters. When the days warm in spring, the larvae become active and grow rapidly feeding between the upper and lower leaves for the balance of the summer. In May the adults force the pupal skin out of the mine, where it hangs for a few days after the fly, a gall midge, emerges. The adult leafminer is a yellow to orange-red fly that looks like a mosquito. Adult flies swarm around boxwoods about the time that the Weigelas bloom. When the boxwood’s new growth appears in spring, the females mate, then insert their eggs into the underside of the leaves. The adult fly dies soon after. The eggs hatch in about 14-21 days into the larval stage ( a maggot) that grows and feeds for the rest of the summer. The leaves develop the characteristic blisters as the larvae feed. The larvae then develop into orange pupae which darken before the adults emerge. One generation of the pest occurs each year.
Click here to read a more in depth article on Leafminer from The Ohio State University.
Box Tree Moth
The Box Tree Moth (BTM) is an exotic insect pest native to North China and Korea which poses a threat to boxwood plantings. Box Tree Moth’s presence in Europe was initially detected in 2006, spreading throughout the continent over the subsequent 15 years primarily from nursery stock shipments. BTM first appeared in New York State in 2021, likely carried on a storm from a recent infestation just across the border in Ontario, Canada. Currently a federal quarantine prevents export of boxwood nursery stock from counties with known infestations.
Boxwoods (Buxus species) are the preferred food source for BTM. There are no native Buxus species in North America, and the lack of host plants in wild habitats limits the spread of the moth. Boxwood is a traditional plant used for topiary and hedges and is the highest-selling evergreen shrub. BTM damage threatens heritage sites, landscaping, and a boxwood nursery trade of over $140 million annually.
Click here to read a more in depth article on Box Tree Moth from The Ohio State University.
Boxwood dieback symptoms include random dieback of twigs with light tan colored foliage. Affected leaves do not defoliate and tend to stay attached to the branches. Root and crowns of affected plants look normal. These symptoms on boxwoods have been long observed in landscape plantings, but were always attributed to phytophthora root rot or volutella blight. The infection also causes bright black discoloration of stem immediately under bark. This bright black discoloration extends all along the infected twigs and differs from discoloration of the crown region caused by phytophthora root rot.
Click here to read a more in depth article on Boxwood Dieback from The Ohio State University.
Generally, boxwood will be less likely to suffer winter damage if it is hardy for the planting zone; appropriate for the environmental conditions, and properly planted and watered. In short, follow the golden rule of gardening: right plant, right place! The following tips will help you find the right place for boxwood in your garden and start you on the best course for protecting boxwoods from winter damage.
Click here to read a more in depth article on Winter Burn from Monrovia.