Box tree pests: box tree moth & co.

Box tree pests: box tree moth & co.

As robust as the box tree sometimes seems, it is not completely immune to pests. Here is our guide to recognising symptoms and treating box tree pests.

The first box tree (Buxus) pest that comes to most people’s minds is usually the notorious box tree moth (Cydalima perspectalis).Unfortunately, the box tree moth is not the only one who loves to attack the beloved shrub. Let us introduce you to the different pests and give you tips on how to get rid of them as soon as possible.

Box tree pests

It is not just diseases that affect the trees and annoy their owners, it is also pests. Various small animals feed on the plant and usually leave behind a sad picture of what once had been a beautiful bush. What to do and which pests you might be dealing with is explained in the following.

Box tree moth

The caterpillars of the box tree moth (Cydalima perspectalis), which originates from East Asia, are often the reason for the destroyed box trees. This article on box tree moth will teach you how to identify the moth and its caterpillars with certainty.  

Box tree moth: symptoms

The insatiable caterpillars occur on the boxwood bushes from mid-March. The adult moths, on the other hand, are rather inconspicuous with their white wings and brown tips. Their ravenous offspring are all too fond of the box trees. The up to 5 cm long green caterpillars have striking black spots on their bodies as well as a black head. First, they make holes in the box tree leaves and with time the caterpillars devour all of the foliage and even the shoots. Because the box tree moth plague begins from the inside of the bush it might go unnoticed at first. The caterpillars later weave webs so the box hedge becomes covered with a silvery coating.

Box tree moth: treatment

If you regularly take a close look at your box tree and also inspect the inside the shrub, you will hopefully recognize the infestation early, because then you can still fight it without any problems. A natural spraying agent is ideally suited for this purpose. There have already been some sightings that native birds have eaten the caterpillars, but this is usually not enough. In addition to natural spraying agents, you can also try to collect the box caterpillars manually or spray them with a jet of water from the garden hose, but always use gloves for safety, as the caterpillars absorb toxins from the box tree. The extent to which these toxins are released by caterpillars is not yet known. You should therefore be cautious when handling box tree caterpillars. You can read more about how to get rid of the box tree moth here.

Mites

Twisted shoots and leaves are caused by a type of mite (Eriophyes canestrinii), which belongs to the gall mite family . Unlike other gall mites, it does not cause galls on the leaves, but deformations.

Mites: symptoms

The mites cause a deformation of the boxwood shoots by feeding on sap out of the plant cells. This causes the leaves and shoots of the box tree to become malformed and the leaves remain small, thin and twisted.

Mites: treatment

In general, mites do not pose a serious threat for the buxus, they are more of an aesthetic problem. If you prune your plant regularly, you shouldn’t have any major problems with mites. If you find individual shoots affected by the mites, simply remove them.

‘Green Mountain’ is a particularly susceptible box tree variety for these gall mites, but there are also varieties that are less sensitive to these mites – such as ‘Herrenhausen’, ‘Faulkner’, ‘Hollandia’ or ‘Handsworthiensis’.

Spider mites

The spider mite (Eurytetranychus buxi) has been introduced to Europe from North America. In 2000, it was first detected on box trees in Germany.

Spider mites: symptoms

Even though they are only 0.35 to 0.48 mm in size, the spider mites are still detectable with the human eye. The boxwood spider mite can multiply extremely rapidly and there can be up to eight generations per year. The damage of these spider mites can be recognized by the bright dots and short lines that look like a comma. This damage is caused by the feeding of the animals because they puncture and damage the plant cells. If the infestation is very strong, the entire leaves become light in colour and, in the worst case, the box tree loses them completely. The mites reproduce best on box trees in sunny and warm locations. They can also be present in places with more shade, but then their reproduction is slower.

Spider mites: treatment

These mites are often preyed upon by beneficial insects such as green lacewings (Chrysopidae) or ladybirds (Coccinellidaei). They can also get washed away from the leaves during summer thunderstorms. However, if you are dealing with a severe infestation or want to prevent an outbreak next season, you can use oil-containing sprays. Using oil products in autumn or spring will eliminate the overwintering eggs of the spider mites.

Boxwood psyllid

Another sucking pest that can infect the box shrub is the boxwood psyllid (Psylla buxi). The larvae and the adult animals are greenish. The larvae form white webs reminiscent of wool under which they hide.

Boxwood psyllid: symptoms

What does the infestation of the boxwood psyllid look like on the box tree? The psyllids feed on the leaves, secrete sticky honeydew and black fungi settle on it. In addition, the larvae form their white waxy wool-like mantle and thus protect themselves from predators and outside elements. By puncturing the leaves while feeding, they make the leaves bend downwards. The space between the leaves shortens and the tips of the shoots resemble small cabbage heads.

Boxwood psyllid: treatment

The boxwood psyllid usually does not make much difference to the box tree and is often eaten by beneficial insects such as spiders, ichneumon flies or lacewings. The removal of infested shoot tips is helpful in combating the disease. However, there were noticeable differences between the varieties, because ‘Blauer Heinz’, ‘Elegantissima’, ‘Angustifolia’ and ‘Herrenhausen’ showed relatively few symptoms, whereas the varieties ‘Pyramidalis’, ‘Green Mound’ or ‘Graham Blandy’ showed very strong symptoms.

Scale insects

Scale insects are sworn enemies of many gardeners. They have a particular liking for ornamental trees and shrubs, fruit trees and rose bushes. The box tree, too, can suffer a scale insect outbreak,  very often caused by the apple mussel scale (Lepidosaphes ulmi).

adult scale insect
Scale insects are common indoor plant pests but they can also target box trees [Shutterstock.com/ Cherdchai Chaivimol]

Scale insects: symptoms

The scale insect is about 2 to 3 mm long and greyish brown in colour. Unlike other species of scale insects, this species does not form honeydew or sooty mildew. However, by feeding on the plant the apple mussel scale impairs the growth of the box tree. With a very strong infestation, the box tree loses its leaves. In fact, entire shoots can die off. Because the box tree sheds its leaves, it is easy to confuse the symptoms with those of the boxwood leafminer. The difference is that you can easily spot the scale insects living on the surface of the box tree.

Scale insects: treatment

Since the insects cannot spread very quickly on the box tree, often only individual branches are affected. These can be easily removed by pruning. However, if the infestation is large and pruning is no longer an option, you can treat the plant with oily sprays shortly after the insects hatch in May or June. But be careful not to act too late, because once the protective shields of the scale insects harden, they are no longer as vulnerable and the treatment can be ineffective.

Boxwood leafminer

The boxwood trees of Europe are unfortunately often afflicted by the boxwood leafminer (Monarthropalpus flavus). 

Boxwood leafminer: symptoms

Approximately 30 eggs per one female are laid directly into the leaves. The female boxwood leafminers die after they lay eggs. These eggs then develop into small larvae that live and feed inside the box tree leaves. They mine their way through the leaves creating corridors, which can easily be overlooked at the beginning of the infestation, as they only appear as light dots on the leaves. Later in summer, the tissue thickens and light brown spots appear on the top of the leaves, which are not as sharply separated from the healthy tissue. Galls form on the underside of the leaf, in which the orange larvae can be found. The shrub can shed leaves. Exactly these galls with the larvae in them are a good distinguishing feature of the boxwood leafminer presence.

Boxwood leafminer: treatment

Normally the leafminers tend to infest older plants and this usually does not cause much damage. However, you can reduce the probability of infestation by pruning the shrub, and if the already present infestation is very strong, you can control the larvae after hatching with insecticides such as Calipso. Again there is a difference between the different varieties, as ‘Handsworthiensis’, ‘Angustifolia’, ‘Herrenhausen’, ‘Faulkner’, ‘Rotundifolia’ and ‘Suffruticosa’ are less plagued by the boxwood leafminer. The ‘Green Mound’ variety from Canada, on the other hand, is particularly badly affected by the leafminer.

A brief summary of the common pests of the box tree:

  • Box tree moth (Cydalima perspectalis)
  • Mites (Eriophyes canestrinii)
  • Boxwood spider mite (Eurytetranychus buxi)
  • Boxwood psyllid (Psylla buxi)
  • Scale insects (Lepidosaphes ulmi)
  • Boxwood leafminer (Monarthropalpus flavus)

Box tree damage: frost damage, sunburn and other

It is not only pests and plant diseases that can damage your favourite evergreen shrub. Environmental conditions can also be responsible for damage and the loss of the lush green colour of the plant. These are the so-called abiotic causes of damage, as they are not caused by living organisms. The following abiotic damage can occur on the box tree:

  • Frostbite and frost damage to leaves and roots
  • Frost drought
  • Snow injuries
  • Sunburn
  • Salt damage

Here you can learn everything you need about boxwood diseases and how to combat them.



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