The borer is correctly called boxwood borer and is a pest introduced from Asia. It can colonize a box tree with countless caterpillars and eat it bare within one season. If it is not stopped, the tree can die. Cutting is a measure.
When and how do pruning measures help with borer infestation?
Overwintering larvae have thick pupae, which is why spraying does not help. You can “cut them away” with early pruningbetween January and Marchbefore they become active again. In summer you should cut back damaged boxwoods vigorously to remove damage and stimulate new growth.
Can I cut the boxwood in any weather?
In winter, the boxwood (Buxus) must not be cut when there is frost. Be sure to wait for a longer frost-free period. Otherwise, the cutting day must befree of rain and overcast, otherwise the risks of burns and fungal diseases are high.
By when does the early pruning have to be done?
As soon as it is warmer than 7 °C outside for a longer period of time, the larvae wake up from their hibernation and begin to eat. In mild years, overwintering can end as early as March. That's why it's important to pruneby March at the latest. The recommendations are even increasingly suggesting that cutting can be carried out as early as January. But since early pruning can lead to frost damage, it is only recommended for infected shrubs.
How do I cut back the boxwood correctly?
In January or February, you can keep pruning minimal by cutting out only areas covered in webbing. To discover them all, you also have to look inside the crown. In March the pruning can be more extensive. The more you cut away, the more larvae you can remove. Box trees damaged by boxwood borer infestationmust be radically cut backby half, both in width and height. Disinfect the pruning tool before and after pruning.
Can I prevent a severe boxwood borer infestation?
There are some preventative measures that can help to detect the boxwood borer early or reduce its population:
- promote natural enemies: great tits, sparrows, predatory spiders, wasps
- Check regularly for infestation from spring to autumn
- Set up pheromone traps in mid-May
- Cover with plant protection nets from mid-May to September (makes egg laying more difficult)
- Sprinkle algae limestone
- inject with Bacillus thuringiensis
Tip
Fertilize weakened boxwood after cutting
After you have cut back an infected boxwood vigorously, it will need plenty of nutrients for new growth. Therefore, fertilize it with a portion of horn meal immediately after pruning.
