Diagnosing Boxwood Problems
Although boxwood are known for having few pests and disease problems, there are a few issues you could run into. This page highlights a few common problems you could run into, and the proper way to identify and treat them. Read through each group and click through the photos for more details.
One of the most common insect pest for boxwood, especially in the Mid-Atlantic region of the United States is Boxwood Leafminer. This small midge-like insect completes its life cycle once per year, emerging in the early spring to mate and lay eggs. This pest is easy to treat with a single, properly timed, insecticide application, or can be prevented by selecting cultivars of boxwood that are genetically resistant. Saunders Genetics has spent many years researching, and learning about this pest. You can read more about Boxwood Leafminer and how to treat it on this page.
This fungal disease that is relatively new to the U.S. might be one of the more severe boxwood problems. First found in North Carolina in 2011, after spreading around Europe for 15 years, this disease can be diagnosed by its distinctly round leaf spots, dark stem lesions, and rapid defoliation, particularly after periods of heavy rainfall and prolonged wet periods. The heavy, sticky spores of this disease spread as water splashes from plant to plant, or on debris and tools. Because of the nature of this disease, there are many biological, chemical, and cultural practices that can help prevent the infection and spread of the disease. Saunders Genetics has spent many years researching, and learning about this disease. You can read more about the biology of Boxwood Blight and how to combat it on this page.
Phytophthora root rot
Phytophthora Root Rot is a soil borne, fungal pathogen that affects the roots of the plant. It is a relatively common disease that affects many different plant species. The pathogen can exist in the soil, but does not become active until proper conditions arise. Prolonged period of wetness, and soil that is saturated with water on a regular basis cause the symptoms to show up. Planting boxwood higher in the soil or even in a raised bed provide proper drainage and minimize chances of getting this disease. Symptoms of the disease start with sections of the boxwood turning off color and leaves feeling dry. Leaves begin to curl and turn brown, but hang on the plant. Stems will also appear to collapse and looks dark and off color. If you cut into the cambium layer of the stem you will see the inside has turn brown and is beginning to rot. The roots of the plants will also turn brown and brittle and the outer layer of the root hair will slough off easily when pulled. See Fig. ** below for examples of healthy and unhealthy roots. There are some chemical control option but the best way to combat this disease is to minimize over-watering and facilitate proper drainage. For more information about site selection and irrigation of boxwood, check out this article.
Boxwood Decline is a bit different than the other pests and diseases that affect boxwood. This issue effects only Buxus sempervirens ‘Suffruticosa’ (English Boxwood) and it is less clear what the cause is. Some believe that it is a single disease and others believe it is most likely the result of multiple stressers, weakening the plant and eventually resulting in death. This problem kills boxwood slowly, starting as a discoloration of foliage, progressing in die-back and eventually killing the plant. This may take months starting on a single branch or section of the plants, and over time it spreads to the entire plant. This should not be confused with Boxwood Blight, which can cause severe damage in a matter of days or weeks.
Stresses that can cause this problem to arise include; losing or removing a large tree that has shaded a plant for many years and is now in full sun, heavy snow causing damage to the branches, severe drought or excessive water, poor soil pH or lack of nutrients, old age, lack of mulch to regulate soil temperatures, or even soil nematodes. Once a plant is stressed, then multiple factors may only worsen the problem. Unfortunately there is nothing to cure the disease, so the focus is to prevent stress that may cause the disease. Focus of proper soil pH between 6.5-7.0 and supply supplemental water in times of drought. If Boxwood Decline decimates a plant, do not replant with another English Boxwood. Look for cultivars such as ‘Winter Gem,’ ‘Green Beauty,’ or other B. microphylla species. NewGen Independence® and NewGen Freedom® are also great replacements for sites that have been effected by Boxwood Decline.