Advertisement

No need to step out of the box, but this landscape staple isn’t without problems

Boxwood is a staple evergreen in many landscapes. Its pleasing form, dark green foliage, and versatility make it a popular choice. Unfortunately, like many plants, it is not trouble free. The challenges with boxwood can have numerous causes, ranging from our variable weather extremes to insects and disease.

Environmental stress

The most commonplace condition is caused by our ever-changing weather patterns. Durable as well as adaptable, it does have its limits. The most common issue is winter injury, which results when our temperatures change rapidly in the fall while the plants are going into dormancy.

A rapid drop in temperature will damage the vascular system or result in leaf burn. Vascular system damage symptoms appear as peeling bark lower in the branches. This damage blocks the flow of water. Winter leaf burn symptoms on the foliage result in twiggy stem and leaf browning, usually a light straw tan color.

The best defense against winter temperature changes is to maintain good consistent soil moisture. Dry conditions, such as our dry spell last fall and winter, can also result in dieback in the plant. Water deeply and thoroughly during times of drought. While boxwood do have some drought tolerance, for best results avoid moisture stress and deficiencies both during the heat of summer and in the fall and winter.

Insect issues

Boxwood is relatively pest free, but we need to address one common pest, boxwood leaf miner. This fly lays eggs on the leaf. When the tiny larvae hatch, they tunnel into the leaf and feed between the upper and lower surfaces of the leaf. The resulting damage is a blistering or puckering to the leaf which will cause it to eventually drop from the plant.

Control of boxwood leaf miner is recommended if you identify the issue. Insecticide sprays can be applied in late May around the time the landscape shrub weigela first flowers. These treatments kill the larvae before they enter the leaf. The other option is a systemic soil drench applied in March and April. These chemicals are taken up by the plant and offer control as insect feeding begins.

Diseases

Boxwood is fairly disease free but not entirely immune. Volutella blight is most common on stressed plants, often due to environmental conditions or poor care. The blight can often be confused with winter injury since similar symptoms appear as stem cankers. Cankers are areas of loose bark which girdles the stem. Other symptoms are tan foliage which can be cupped or curled. Orange rusty pustules can be seen on the underside of the dead foliage.

Control is difficult and not recommended in the home landscape. Prune out any dead wood, provide good care and in most cases the plant will recover.

Blight is the most serious of all boxwood issues. Blight results in defoliation and death of the plants. The classic symptom is black cankers and streaks on the stems. This issue is most common in nursery production and parts of the country where conditions are more favorable for disease development. Boxwood blight cases in the Kansas City area are extremely rare and highly unlikely.

Boxwood is a good choice for the landscape even with these problems. We have few options for evergreens and given appropriate care the boxwood will add beauty with minimal effort.

Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Have a question for him or other university extension experts? Email them to garden.help@jocogov.org.