How to keep your box plants healthy
Box plants (Buxus) are incredibly versatile and attractive plants in any garden or landscape. They provide high impact evergreen structures, and their slow growth is ideal for hedges and topiary.
Unfortunately, box plants in the UK are under attack from two serious problems; the box blight fungus and the box tree caterpillar. The good news is that with a small amount of care and attention, these problems can be managed.
Managing box blight
In the same way that rose growers can expect to encounter rose blackspot, box growers will inevitably encounter box blight at some point. The fungus (Cylindrocladium buxicola) is particularly problematic in mild wet weather.
Here are some simple steps you can take to reduce the impact of box blight:
- Boost the vigour of the plant with a regular foliar feed such as Topbuxus Health mix. Vigorous healthy plants are better able to withstand disease.
- Disinfect your tools before and after working in a garden with box plants.
- Clip box hedges and topiary in dry weather between May and August. The sticky fungal spores are produced in damp conditions and are easily spread between plants on tools. Spores occur in the highest numbers in spring and autumn.
- If you notice box blight, treat it promptly with a fungicide approved for use on ornamental plants1.
- Infections on mature plants can be pruned out and disposed of. Box blight does not infect the roots of the plant, and the shoots will slowly regrow.
- Apply a protectant fungicide in spring and autumn when the blight fungus is most likely to infect your plants. It can also be beneficial to apply a preventative fungicide before clipping box plants.
- Sweep up and dispose of fallen box leaves (do not compost). The fungal spores can survive on fallen leaves for up to 6 years and act as a future infection source.
- Encourage an open structure and looser form where possible. Tightly clipped plants are more prone to blight.
- Ensure that plants are well spaced where possible and not covered by overhanging vegetation. Crowding creates humid conditions and encourages the box blight fungus to grow.
- Avoid highly susceptible box varieties, including Buxus sempervirens ‘Suffruticosa’. Buxus microphylla ‘Faulkner’ appears to be less susceptible to box blight.
Managing the box tree caterpillar
Here are some simple steps you can take to reduce the impact of the box tree moth:
- Isolated caterpillars can be removed by hand. They often shelter between leaves and webbing so careful searching is needed.
- Prune and dispose of shoot tips of infested plants in the winter. Young caterpillars overwinter between leaves in the shoot tips.
- Extensive infestations can be treated with an insecticide. The caterpillar hides within silken webbing which means that insecticide sprays need to be forceful enough to penetrate the webbing and thoroughly coat the plant.
- The natural biological insecticide Bacillus thuringiensis var kurstaki selectively kills caterpillars and is very effective in treating box tree caterpillar. This is available as a licenced professional product1.
- Organic contact pesticides are effective but will need repeated applications. More persistent synthetic insecticides are also available.
- The nematode biological control sold as ‘Fruit and Vegetable Protection’ has been shown to reduce caterpillar numbers.
- Gardeners have seen jackdaws and bluetits feeding on the caterpillars. Encouraging wildlife may therefore have the added benefit of reducing box tree caterpillar populations.
If you would prefer not to think about box blight or box tree moth, many plants can be used as an alternative.
Traditional green replacements:
- Ilex crenata
- Euonymus japonicus
- Pittosporum tenuifolium ‘Golf Ball’
- Taxus baccata
- Lonicera nitida ‘Maigrun’
- Osmanthus x burkwoodii
Or something a bit different:
- Lavandula angustifolia
- Berberis darwinii
- Photinia ‘Little Red Robin’
- Pittosporum tenuifolium ‘Gold Star’
Please note that all professional chemicals should be applied by a licenced user and applied according to the label instructions. Chemicals should be tested initially on a small area of the plant to rule out adverse reactions. Alternating between two or more different fungicides can reduce the likelihood of the fungus becoming resistant.
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Posted 6th Apr 2:22pm