Boxwoods are commonly used as a hedge or screen in many landscape designs. According to NC State University, there are more than 160 registered boxwood cultivars. Boxwoods are susceptible to certain pests and conditions that cause leaves to turn orange or bronze.
Cold Weather Damage
Boxwoods can develop discoloured foliage if damaged by cold weather. Boxwoods exposed to cold temperatures, frost and blowing wind can sustain winter injury. Winter weather is more likely to affect plants under stress from drought or low pH. The primary symptom associated with winter injury in boxwoods is foliage turning orange, yellow or red known as bronzing. According to NC State University, it is normal for certain boxwoods such as the Japanese boxwood to develop symptoms of bronzing each year. Planting your boxwood in a shady area protected from the bitterly cold winds reduces bronzing. After winter bronzing, boxwoods usually develop healthy, green leaves the following spring.
English boxwoods are susceptible to decline, which occurs slowly over the course of time. The symptoms associated with English boxwood decline include light-coloured leaves in certain areas of the plant that gradually turn orange, bronze, green and brown. Leaves fall from the shrub and continue until the boxwood is bare. Providing the best growing conditions possible is often effective in reducing English boxwood decline. Preventing stress from drought and avoiding winter injury often reduces the risk of decline. Good sanitation practices such as removing and destroying plant debris can also prevent English boxwood decline.
Nematodes can adversely affect the boxwood. The most common nematode in boxwoods is the lesion nematode, followed by root knot, ring and boxwood spiral. Nematodes are very small, unsegmented roundworms that live in wet soil particles. The symptoms associated with nematodes in boxwoods include stunted growth, leaf drop and orange or bronze foliage. Preventing nematode infestation in boxwoods is best accomplished by fertilising regularly and frequent watering to avoid stress from drought.