Your thuja suddenly turns brown? Not always a disease is to blame. Too much sun in summer or the road salt in winter can also be responsible. How to find out what is responsible for the brown discoloration of your thuja, you will learn here.
Thuja, also called tree of life, is very appreciated in our country as a hedge plant. Although the thuja as a cypress plant does not have needles, it belongs to the conifers. It has so called scale leaves – small leaves closely attached to the shoot. The arborvitae as a hedge is a completely opaque evergreen plant screen. It grows very quickly and is also hardy. Although the habitat is considered hardy, it can also become a problem child: When the thuja suddenly turns brown dies. We explain the most common causes of brown shoots here.
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The discoloration of the Thuja in winter
As winter approaches, thuja trees change color to adapt to the extremely cold and dry weather of their native North America. So don’t fret if your thuja hedge turns rusty brown by winter. Thuja wild species, such as the Occidental arborvitae or giant arborvitae, show a bronze winter coloration. Cultivated forms discolor less or even retain their green hue.
Thuja turns brown: this may be the reason
- road salt
If your thuja hedge is close to the road, it may suffer damage when road salt is used. This is because the thuja is sensitive to salt. A typical road salt damage is the browning of the branch tips in the ground area of the plant. Here the salt concentration is very high and the thuja is also hit by splashing water. For damage caused by salt, it is best to cut the plant back thoroughly and then rinse it off. Well-intentioned watering will shift the salt to deeper soil layers. - overfertilization
The thuja can also turn brown if you have fertilized too much blue corn. This is because this fertilizer also causes the salt content in the soil water to increase. - dried up Thuja shoots
Drought does not mean good things for all Thuja species. They, like other evergreen plants, have a delayed response to the lack of water. The exact cause of the dried, yellow-brown shoots can then only be guessed at. If you have ever kept your thuja hedge too dry, water it thoroughly. In addition, the soil should be conscientiously worked with bark mulch – so you protect the hedge from drying out again. In the summer, if there is too much sun and not enough water, it is possible that sporadic leaf burn will appear. - acidic soil harms the thuja
Too much manganese in the soil also causes brown-black needle discoloration in Thuja. To save the too acidic soil, first mix it with carbonic acid lime. About three months later, add mature compost and the soil will again have a balanced nutrient ratio. However, before you just start liming, check the pH of the soil with a test kit from the garden center.
Diseases on leaves and shoots
Thuja is more or less susceptible to various fungal diseases. Pestalotia shoot dieback is probably the best known. The fungus Pestalotiopsis funerea is a weakness parasite. It is characterized by twig dieback from the outside in. Black-brown, pinhead-sized, round fruiting bodies form on the shoots. These then continue to produce spores of the fungus.
The fungus Didymascella thujina causes scale or needle blight. Mainly older leaf scales are affected by this disease. Round to oval, brown-black fruiting bodies then appear on the affected scales in the spring. These also form further spores and thus infect other plants. The fungus spreads mainly in areas of high humidity and therefore occurs more frequently on the lower, shaded parts of the thuja. Kabatina shoot dieback is another widespread disease of trees of life. This fungus usually affects the young, soft shoot tips, causing them to die. Plants on acidic soils are especially susceptible to this disease.
By timely recognition and consistent control of the diseases, they usually do not pose a major threat to the thuja. To do this, simply cut back the affected plants and treat them with appropriate fungicides at two-week intervals. To prevent fungal infestation, it is best to ensure that the soil is rich in humus and loose when planting. A good water and nutrient supply is also important here.
Thuja root rot
The most dangerous disease for thuja is root rot. It destroys the entire bark tissue of the roots. Initially, the shoots turn yellow, then brown. Finally, the thujas die completely. Young thujas usually do not survive even one season with the root rot. Even if initially only individual plants in the hedge are affected, the root rot can spread very quickly. Therefore, they should immediately remove infested plants from the hedge.
Again, timely identification of the disease is crucial for its successful control. You can fight the fungus with fungicides. However, you should replace the soil before replanting, as the fungal spores can remain in the soil for a very long time and in turn infect the new plant. You can prevent root rot by creating a good soil for the thujas and taking good care of the hedge.
Pests on the thuja
By feeding on the bark of young thuja shoots, the thick-mouthed weevil causes the tips of the shoots to brown. Against him you can act with nematodes. The larvae of the thuja leaf miner also cause brown spots on the thuja. It eats tunnels in the leaf scales. To get rid of the larvae, cut back your hedge often.
However, unlike the thuja bark beetle, these insects do not normally cause major damage. It can damage the bark tissue of the arborvitae so badly that it dies. A sure sign of this pest is small holes drilled in the trunk. Once the bark beetle has infested a thuja plant, the only thing that can be done is to dig it up, chop it up and dispose of it – if possible in winter, as this will allow you to dispose of the hibernating beetle directly.
