Boxwoods are a staple in many landscapes. These ornamental, evergreen favorites make excellent hedges or edging, but can also serve as foundation plants. However, this popular plant is not without its issues. There are a number of common problems, which include insect pests and diseases. As with any plant in your landscape, it’s important to understand the issues that can impact their health.
Pests of Boxwood
Psyllids, mites and leafminers all feed on the foliage of boxwoods. An infestation of boxwood psyllid is generally less serious. While the presence of these insects isn’t devastating, the damage resulting from feeding can be unsightly. Leaves, particularly young, new growth, will have a cupped appearance. Nymphs may be visible inside the cupped leaves. Another pervasive pest is boxwood mite. As they feed, they inject a toxic saliva into the leaves. As a result, leaves will become stippled with small white or yellow marks. Mites are tiny and infestations sometimes go unnoticed until damage is widespread.
Depending on geography, the most destructive and serious foliage feeder is often boxwood leafminer. Some cultivars are more resistant than others. Larvae feed and live inside the leaves. A single leaf can contain ten or more larvae. A major infestation left untreated can lead to death of the plant.
Another pest to watch for is box tree moth. It is a widespread invasive pest in Europe that has now been found Canada in 2018 and the United State in 2021.
Diseases of Boxwood
Boxwood is susceptible to phytophthora root rot. This fungal disease develops primarily on wet, poorly drained soils and is a leading cause for the death of this species. Boxwood blight is another fungal disease that poses a serious threat. It causes leaf spots, defoliation, twig and branch cankers, dieback and death of plants. Consequently, it is critical to be careful when adding new plants to a landscape. Planting a boxwood species that is more resistant to the boxwood blight is a smart choice.
Additional diseases such as volutella blight are also relatively common for both American and English boxwood. The latter is susceptible to what is commonly referred to as “boxwood decline.” This disease causes a progressive deterioration in vitality. American and littleaf as well as hybrids appear to be resistant.
Other Common Concerns
Boxwoods prefer partial shade and protection from the afternoon sun. When planted in full sun, winter injury, sunscald and desiccation are more prevalent concerns. Further, these plants have a shallow root system. Soil should be well drained and a light layer of mulch applied to encourage root growth. Regular pruning to remove small branches in the outer canopy will help allow light and air to penetrate to the center. The dormant season is the best time to prune.
Ultimately, remember that consideration of your site and planting conditions as well as routine care of boxwood will help keep these plants healthy year-round.