Green velvet boxwoods (Buxus microphylla var.koreana ×sempervirens "Green Velvet") are members of the genus Buxus, which is part of the Buxaceae plant family. Green velvet boxwoods are easy-to-grow shrubs that will grow in most soils and are hardy in U.S. Department of Agriculture plant hardiness zones 6 through 9. However, Green velvet boxwoods, like all boxwood species, are susceptible to a few insect and disease problems that can lead to decline of your shrub.
Phytophthora Root Rot
The fungi Phytophthora cinnamomi and Phytophthora nicotianae can cause boxwood leaves to turn light green and the roots to darken, peel and rot at the crown. Phytophthora root rot of boxwood plants is favored by moist, warm soil conditions, and infection is typically more serious in heavy clay or poorly drained soils. Chemicals are often ineffective to control phytophthora root rot, but it can be prevented by planting boxwoods in well-drained soil or raised beds. According to the University of California, when used in combination with proper cultural practices, fungicides containing fosetyl-al may provide preventive control for healthy boxwoods.
Boxwood canker (Volutella buxi) causes branches or entire plants to fail to produce new growth. Infected leaves also turn light green to tan in color and turn upward so that they lie close to the stem. Diseased leaves and branches may also have waxy, pinkish fruiting bodies. The bark at the base of infected branches peels away, revealing gray to black discoloration beneath. Remove dead branches and leaves, and apply fixed copper or Bordeaux fungicide to prevent spread of infection to healthy branches and leaves. Read and follow all directions on the fungicide label for rates and timing.
Several species of nematodes can be problematic for green velvet boxwoods, including Southern root-knot nematode (Meloidogyne incognita), lesion nematode (Pratylenchus), stunt nematode (Tylenchorhynchus) and ring nematode (Mesocriconema). Symptoms of nematode infestation of boxwood include bronzing of leaves, stunted growth and decline. Boxwoods attacked by nematodes will also form lateral roots above the affected area that are also infested. Good cultural practices, such as mulching, adequate water and proper fertilization, can prolong the life of boxwoods infested by nematodes, but it is extremely difficult to eradicate them from the landscape completely. The best method of managing the problem is to keep nematode populations low enough that they cannot seriously damage your plants. Grow boxwoods with plants such as grasses or marigolds, which are resistant to nematodes and will help reduce populations.
The boxwood leafminer (Monarthropalpus buxi) can be a serious problem or boxwoods. Leafminers are actually the orange-colored larvae of small flies, which are also orangish in color. Leafminers hatch inside boxwood leaves, creating mines as they feed inside. They overwinter in the leaves, and the adults emerge the following spring. Leafminer feeding causes irregular shaped bumps on the upper leaf surface and blisters on the undersides. Leaves also turn yellow or brown and drop earlier than healthy leaves. Heavy infestations can cause rapid defoliation and plant death. Chemical control of leafminers is only recommended if the infestation is severe. Insecticides such as malathion and carbaryl may be effective on adult leafminers when applied in mid-April to early May. Foliar systemic insecticides containing acephate are effective on leafminer larvae, and soil applications of dinotefuran or imidacloprid may also provide some control.
- Pascoe’s Plants: Green Velvet Boxwood
- Clemson University Extension: Boxwood Diseases and Insect Pests
- University of California Extension: Phytophthora Root and Crown Rot in the Garden
- University of California Extension: Pseudonectria Canker — Pseudonectria Rousseliana (Conidial State Volutella Buxi)
- University of California: Boxwood Leafminer -- Monarthropalpus Flavus
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