I have boxwood hedges with periwinkle growing inside, but the boxwood looks sparse with yellowing leaves. It’s facing the East so it gets morning sun, and doesn’t appear to have a pest problem. Can it still be salvaged?
Thank you for contacting Toronto Master Gardeners about your Boxwood problem. If you have looked closely at the leaves and there are no white cocoons or individual leaves attached together with webbing – then hopefully your hedge is not infested with Box Tree Moth. I have included links to this pest because it is decimating hedges at an alarming rate.
Yellowing of leaves can be caused by:
1. Root Rot which results from a fungus (Phytophthora) manifesting as yellowing leaves. They curl inwardly and the plant does not thrive. Increasing drainage around the plant’s roots and reducing watering may help. There is no chemical to aid in recovery.
2. Nematodes are microscopic roundworms that also attack the root system. Plants will yellow and die back. Even if you water and fertilize the plants, they will not survive in the long run. Replacing them with nematode-resistant American boxwood or holly is an option.
3. Macrophoma Leaf Spot shows up as yellow or tan coloured leaves with black fungus in small spots on the leaves. Prune out diseased branches to improve air circulation.
4. Volutella Stem Blight or Canker causes leaves to go from green to a straw colour. Prune out diseased branches to improve air circulation. Below is a detailed description of common boxwood afflictions:
Unfortunately in Toronto and surrounding area, Box Tree Moth is prevalent. Gardeners are trying to cope with this recent threat to boxwood. Landscape Ontario is doing its best to research and combat this pest. They defined the difference between Box Tree Moth and LD Moth in the link below:
Toronto Master Gardeners have received many questions about this problem and links are below:
Toronto Master Gardeners developed a definitive Gardening Guide on Box Tree Moth:
Identifying the boxwood problem is your first job. If there is any doubt then consult a landscape professional. Landscape Ontario can recommend reliable contractors. Best of luck with your boxwood and remember there are always native and disease resistant alternatives in the future.