I have a 15-year-old box hedge (Buxus sempervirens). In the past five years I’ve fertilised it with chicken pellets around the roots each March and also sprayed it with TopBuxus every five weeks from March to September, followed by pruning every October. This year I noticed that a two-metre section of the hedge had brown leaves with a white tip or edge. According to the RHS website, this could be Eurytetranychus, a mite specific to box. But I’m also concerned that it might be the start of the dreaded box blight.
There are so many different types of advice given, from pruning the centre and cutting back the foliage to using anti-caterpillar spray, to checking by scratching the stems for green bark as an indication of how far the plant has been affected. I would really appreciate your advice on this. John Duggan, Co Clare, Ireland
Grown in many Irish gardens and traditionally considered a reliably handsome, hardy evergreen shrub suitable for tight clipping, box (or Buxus sempervirens as the most commonly used species is properly known) has come under serious attack from a few very destructive non-native pests and diseases in recent years. One of these is box blight, a fungal disease (technically two closely related diseases) most active in wet weather. It causes patchy dieback, browning of leaves and defoliation. Left untreated, it will eventually kill even well-established plants. Once a plant is infected, the disease can’t be eradicated but can still be effectively controlled by regular use of either liquid seaweed or a proprietary product such as TopBuxus Healthmix as a foliar spray throughout the growing season, combined with fastidious garden hygiene.
Annual pruning in late July/early August is also advised, using sharp, clean clippers regularly dipped in disinfectant throughout the process. It’s also very important to immediately collect and bin all prunings and fallen leaves that could act as a source of infection.
TopBuxus Grow is recommended as a fertiliser to use in combination with TopBuxus HealthMix. But avoid the use of chicken pellets, which are high in nitrogen and encourage the production of soft, sappy growth that’s particularly vulnerable to attack.
A multipronged approach with very carefully timed interventions is essential to disrupt their life cycle
Box caterpillar (Cydalima perspectalis), or box moth as it’s also known, is another relatively newly introduced threat to box. The damage is caused by caterpillars, which either overwinter in a hibernatory state on the underside of the foliage where they are protected by dense webbing or else hatch out from eggs laid by the adult female moth. Once they start actively feeding in March on the leaves of the plants, they can rapidly defoliate an established hedge in a matter of days. Again, a multipronged approach with very carefully timed interventions is essential to disrupt their life cycle.
As soon as you see signs of the caterpillar feeding in early spring, the organically acceptable biological insecticide (Bacillus thuringiensis, Bt) needs to be applied as a foliar spray at regular intervals starting in March-April, then again in mid-July, mid-August, mid-September and mid-October. Choose a dry day (minimum of 15 degrees) with no rain forecast to fall for at least six hours after spraying. All parts of the plants must be sprayed.
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This biological insecticide is available as LepinoxPlus from fruithillfarm.com and as TopBuxus Xentari from most good garden centres. It’s also effective against box mite (Eurytetranychus buxi), although the latter isn’t considered a serious threat. Pheromone traps that obstruct the male box moth from mating with the female are also very useful. So is handpicking and disposing of the caterpillars.
For more detailed advice on effectively managing these pests and diseases, visit ebts.org as well as topbuxus.com and betterbuxus.com
