Boxwoods are susceptible to several parasitic nematodes (microscopic round worms), including the Southern root-knot nematode (Meloidogyne incognita), ring nematode (Mesocriconema), the lesion nematode (Pratylenchus), and the stunt nematode (Tylenchorhynchus).

Symptoms consist of leaf bronzing, stunted growth and general decline of boxwood. The microscopic worms feed on the roots, which soon die and the plant forms lateral roots above the invaded area. These lateral roots in turn are infested. Repeated infestations and lateral root production result in a stunted root system resembling a witches’ broom.

Prevention & Treatment: The life of infested plants may be prolonged by providing good care (fertilization, mulching) and by watering the plants thoroughly during dry spells. American boxwood (B. sempervirens) is resistant to root-knot nematodes and tolerant to stunt nematodes. Nematodes cannot be totally eliminated from the landscape. The goal is to keep the population low enough to prevent damaging symptoms that weaken the plant. Boxwoods should not be grown in soils heavily infested with nematodes. Growing plants that are not affected by nematodes (grasses, marigolds) will reduce nematode populations in the long term.

Nematode-tolerant shrubs such as yaupon holly and Burford holly can be used to replace boxwood, which are killed by nematodes.