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Thuja or tree of life, as the plant is also called, is one of the robust plants. Nevertheless, pests can cause considerable damage to Thuja hedges and promote diseases. Therefore, it is crucial to fight parasites early. As a layperson, however, it is not always easy to identify the type of pest in question. We explain what needs to be considered and what can be done against a pest infestation.

Pests on Thuja hedges

An infestation with pests is rather rare in the tree of life. If damage to hedges or solitary plants is noticed, only a few insects come into question. These include:

  • Thuja leaf miner
  • Juniper leaf miner
  • bark beetle
  • scale insects
  • spider mites

Thuja leaf miner

The butterflies are difficult to distinguish. However, they do not damage the plants either, they only lay their eggs on them. When the larvae hatch, they feed on the leaves and shoots. The adult leaf miners fly between June and July. The larvae can also hatch between August and September in the following year. An infestation can be identified at the following points:

  • Leaves and shoots that first become transparent, then turn brown and die
  • black dots from faecal deposits
  • brown caterpillars
  • Feeding tunnels in the leaves and on the shoots
Thuja leaf miner. Argyresthia thuiella

Juniper leaf miner

The juniper leaf miner can also stray onto the thujas and can be identified by the above spots. Only the flight time of the insects differs. They are already active from May. Accordingly, the damage can occur earlier in the year. In terms of damage and control, however, it does not differ from the Thuja leaf miner.

Juniper leaf miner, Argyresthia trifasciata

Combat leaf miners

If the damage described is found on hedges or individual trees, the overall condition of the plants should first be checked. With otherwise healthy and vigorous plants, it is usually sufficient to simply cut off and dispose of the affected shoots. However, they should not end up on the compost, since the pests could spread from here again.

In the case of already weakened plants or a severe infestation, control must be carried out in two ways. On the one hand, a strong pruning must be carried out in order to remove as many of the caterpillars and other eggs as possible as well as the already damaged parts of the plant. In addition, an appropriate pesticide from a specialist dealer must be used.

bark beetle

Another Thuja pest is the bark beetle. It only affects thujas when they are already weak and suffering from drought. Therefore, hedges should also be watered regularly and abundantly if necessary and especially shortly after planting. The adult beetles bore into the bark and lay their eggs here, similar to leaf miners. The consequences include:

  • dead shoots
  • visible larvae on the leaves
  • Drill holes and discoloration on the bark of the branches
  • Traces of feeding on the leaves

The large, brown bark beetles or their larvae can cause considerable damage to the tree of life and destroy entire hedges.

Bark beetle feeding marks

Fight bark beetles

Due to the high potential for damage, an infestation with bark beetle larvae should be dealt with immediately. Similar to combating leaf miners, affected parts must be removed and destroyed. In addition, an appropriate pesticide should be used to kill any remaining eggs and larvae.
It is also important to strengthen the tree of life and water it sufficiently to prevent further infestation.

scale insects

Scale insects rarely appear on Thuja hedges and cause little damage in comparison. The small pests are visible to the naked eye and are often found on the underside of the leaves of thuja hedges. They also cause grazing marks.
On the one hand, appropriate pesticides can be used to combat it. On the other hand, natural predators can also be used. These include:

  • ladybug
  • lacewings
  • parasitic wasps
  • hoverflies
  • predator beetle

Extra tip: The beneficial insects or predators should be bought early in specialist shops or online, as they are usually available as eggs or larvae and therefore need sufficient time before they can fight the parasites.

spider mites

A spider mite infestation is expressed by white webs between the leaves of the thuja. The pests mainly appear on thuja hedges when the plants are warm and dry. A good means of prevention is therefore sufficient watering of hedges and individual plants. In addition, they can be sprayed with water occasionally, because moisture does not do the spider mites any good.

Spider mite infestation

If an infestation has already occurred, the affected parts of the plant can be cut off and destroyed. If possible, they should be burned or disposed of with household waste to prevent the parasites from spreading again. In addition, various plant broths can be used to spray the trees of life. Below:

  • tansy
  • vermouth
  • field horsetail

Alternatively, ready-made agents for spraying the plants against Thuja pests can also be purchased in specialist shops. Products with neem oil, for example, are well suited.

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