Boxwood Decline

From the Pests of Ornamental Series

John F. Baniecki, Ph.D.
WVU Extension Service
Plant Pathology and Entomology Specialist

The symptoms of this decline are the loss of color in definite areas of the plant with the foliage becoming gray-green, then yellow or even straw colored. This results in the death of entire branches, generally in the apical and middle portion of the crown. The bark of these branches becomes separated from the wood in most instances, and when cut, the wood is discolored by brown streaks. This condition generally results in death of whole plants.

The decline of boxwood has been attributed to various causes, such as poor soil drainage, infertility of the soil, poor rooting of transplants, setting plants too deep in the soil, or winter injury. However, more recently nematodes and soil fungi have been suspected of being causal organisms.

In general, vigorous growing plants are less subject to insects and diseases and the following facts are presented to help you grow more vigorous boxwoods:

  1. Boxwood roots require moist, cool growing conditions, so mulch with peat or leaf mold.
  2. A well-drained soil is required, so do not plant in poorly drained locations.
  3. Water boxwood plants only when necessary, being careful to soak the soil completely. Frequent light spraying is detrimental. Slack off watering after midsummer so plants will not be "soft" when entering the cold weather.
  4. Plants should be protected from drying winter winds or severe low temperatures by the use of screens. Be sure that there is an air space between the plants and the screens.
  5. Young plants should be shaded from hot sun in the heat of summer for the first year or two after transplanting.
  6. It may be helpful to spray the foliage of recently transplanted specimens on summer evenings to keep foliage in good condition during the first dry months of growth in the new location.
  7. Do not plant boxwood too deeply--be careful to keep. the original soil line level when transplanting.
  8. Two species of fungi, Volutella buxi and Macrophoma candollei, are common saprophytes on dead and weakened plant parts. To eliminate this problem, the interior of boxwood plants should be cleaned annually of all accumulated debris, such as dead branches and leaves. This practice will also increase the aeration of the interior of the plant and result in healthy interior growth.
  9. Boxwood is a heavy feeding plant and should be liberally fertilized in order to develop a -vigorous growing plant. The amount of fertilizer applied depends upon (1) the size of the plant being fed, and (2) the rate of growth desired by the grower.
  10. To obtain overall vigorous growing boxwood plants, apply commercial fertilizer (5-10-5, 5-10-10, etc.) in holes approximately one foot apart and eight to twelve inches deep. These holes should be made within the crown area as well as around the periphery of the plant. Use care in making holes so as not to injure the larger roots of the plant. Do not fertilize late in the growing season.