Leaves on boxwood shrubs turn yellow and leave the plant looking diseased for many reasons, including damage from the cold weather, root rot and nematodes. English boxwood decline causes the leaves to bronze and then turn orange, yellow and brown before falling off the shrub. leaving only the stems.
Yellowing due to harsh weather conditions most often occurs with Japanese boxwood plants. They suffer from frost and wind combined with bright sun exposure. When the plant exits the dormant season, it normally replaces the damaged leaves with new growth. Moving plants to a shaded location or providing a windbreak helps to prevent this damage.
Root rot is a fungal disease affecting boxwood. Without intervention, it causes the death of the plant. Planting boxwood in well-drained soil or raised beds helps to prevent root rot. Early treatment of the soil with a fungicide sometimes saves a plant showing signs of damage.
Nematodes are parasites that feed on the roots of a plant. They are difficult to control and chemical treatment requires hiring a licensed professional. Healthy plants can survive some damage from nematodes, so it is important to plant them in well-drained soil and provide sufficient irrigation during dry weather.
The best prevention for English boxwood decline is establishing healthy plants. Owners should provide protection from the cold, water the plants and remove plant debris, which sometimes harbors the disease.