How to Treat and Prevent Boxwood Diseases

Hubert Fontaine discusses the primary insects and diseases that affect boxwood plants. This summary provides an in-depth look at the main fungal diseases and pest issues, as well as prevention and treatment methods to ensure healthy boxwood growth. *Fungal Diseases Affecting Boxwood* Two major fungal diseases commonly attack boxwoods: 1. **Volutella Buxi**: This fungus targets the roots, causing the boxwood to wither and turn reddish-brown. While it may appear that the plant is either thirsty or suffering from spider mites, the actual cause is Volutella Buxi. 2. **Cylindrocladium buxicola**: This fungus affects the foliage and stems. The initial symptoms include light spots on the young leaves, surrounded by a reddish ring. These spots quickly merge, leading to the drying and eventual fall of the leaves. The disease thrives in stormy weather conditions characterized by high temperature and humidity. *Combatting These Fungal Diseases* **Moisture Control**: Avoid excessive moisture, as boxwood plants in clay soil are prone to yellowing. **Nitrogen Levels**: High nitrogen levels exacerbate fungal attacks. Boxwoods planted near lawns are more susceptible. **Pruning Practices**: Prune less frequently and avoid cutting too short. Ensure cutting tools are well-disinfected. **Weather Considerations**: Never prune during rainy weather, as water helps to spread fungi. **Removing Infected Plants**: Uproot and discard any dead plants. **Fertilization**: Use specialized boxwood fertilizers and avoid nitrogen-rich lawn fertilizers. **Planting Conditions**: Space plants adequately during planting and avoid damp soils during winter. **Leaf Management**: Regularly rake fallen leaves around the base of the boxwoods. For enthusiasts of topiary art, sick boxwoods can be replaced with Lonicera nitida, which are easy to grow and prune. *Prevention Measures* **Soil Drainage**: Ensure well-drained soil during planting, as boxwoods do not tolerate overly wet soils. **Organic Amendments**: Provide annual organic amendments to prevent nutrient deficiencies that weaken the shrubs. **Irrigation Practices**: Avoid watering the foliage. **Tool Sanitation**: Always disinfect pruning shears before use. **Disposal of Infected Parts**: Cut and burn all diseased parts. **Replanting Protocol**: Do not replant in soil where a diseased plant was recently removed. **Equisetum Decoction**: Water with horsetail decoction every ten days in spring and summer. **Bordeaux Mixture Treatment**: Treat with Bordeaux mixture at the end of winter. *Boxwood Moth Control* **Trapping Males**: From March to late September, the boxwood moth can produce 2 to 4 generations, depending on weather conditions. Prevent egg-laying on the underside of boxwood leaves by setting up pheromone traps to capture as many male moths as possible, thus stopping them from mating. **Caterpillar Elimination**: Inspect previously affected boxwoods and nearby healthy plants every 2-3 weeks for young caterpillars, looking at the core of the boxwood clumps. Treat caterpillars measuring about 1 cm with Bacillus thuringiensis solution—a later treatment will be ineffective. Repeat treatment with each new generation of caterpillars. *Selecting Resistant Boxwood Varieties* Most Buxus sempervirens varieties (except ‘Dee Runk’ and ‘Fastigiata’) are vulnerable to fungal diseases. Slow-growing shrubs such as B. microphylla ‘Green Beauty’, which are not over-fertilized or frequently pruned, tend to have greater resistance. In summary, maintaining healthy boxwoods requires vigilant care in terms of planting conditions, moisture control, proper pruning practices, and timely treatments against pests and diseases. By adhering to these guidelines, it is possible to mitigate the impact of fungal diseases and pests on boxwood plants.