In my last post I introduced you to two of the most common and nasty pests which destroy buxus plants, namely the Box Tree Caterpillar – Cydalima perspectalis and Box Blight – Cylindrocladium buxicola. In this post I will look at identification, treatment and prevention of these two pests.
Box Blight Cylindrocladium buxicola
Cylindrocladium buxicola is a fungal disease. Colonies of dormant mycelium can exist on plants for up to six years waiting for the ideal conditions to send out spores and spread infection. Telltale signs of infection to look out for are:
- Brown spots on your buxus leaves
- Black streaks on stems
- Severe die back leading to bare dead looking plants
- In wet conditions you may even notice white spore masses of the fungus on the underside of infected leaves
If you have identified any of the above symptoms you must act quickly to avoid further spread of the disease. Here are some of the steps I recommend:
- Remove and burn any infected foliage
- If any plants are severely infected you may want to uproot the entire plant to avoid spread to other healthy plants
- Remove dead leaves and the first layer of top soil from under any infected plants
- Once you’ve removed infected plants, spray remaining foliage with a fungicide.
The old adage “prevention is better than a cure” couldn’t be more apt when it comes to box blight. Here are some relatively simple recommendations many of which are part of a good gardening hygiene regime which can help across the board when it comes to horticultural pests and diseases:
- Quarantine any new commercially sourced plants for 3 to 4 weeks before adding them to your garden
- Only prune your buxus during dry weather. Box blight spores spread best when it is warm and damp and freshly pruned plants are most susceptible to airborne infection.
- Use a fungicide for preventative spraying both a week before pruning and a week after pruning.
- Water your buxus at root level – do not water from above – try to keep the foliage as dry as possible
- Use a straw based mulch around the roots
- Disinfect tools before and after pruning
Box Tree Caterpillar – Cydalima perspectalis
The brown and white box moth lays its pale yellow flattish eggs in overlapping sheets on the underside of box leaves. The young caterpillars are light green with a black head and develop into 3-4cm green adults with black stripes. You will notice your bush is infested very quickly as it withers under the caterpillar attack with only the leaf veins and stems remaining. You will also see white webbing which is produced by the caterpillars festooning your buxus bush.
Manual removal of the caterpillars obviously helps but it is painstaking and time consuming. There is a product only available to agriculture in the UK called XenTari which is really good at eradicating these caterpillars. You can however buy it from Europe and get it shipped to the UK.
As with most garden pests it is difficult to prevent. Keep your eyes out for signs of the caterpillar and destroy them at first sight. Pheromone traps may be used to trap adult moths and prevent them from laying eggs.