Thuja hedge: tips against brown shoots


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The Thuja, also called tree of life, is appreciated by many hobby gardeners as a hedge plant. It belongs like the spruce and pine to the Nadelgehölzen, although it does not possess any needles as Zypressengewächs (Cupressaceae). Instead, she wears small leaves that fit closely to the shoot. In technical jargon these are called scale blades. Thuja has many advantages as a hedge plant, because it grows quickly, forms an absolutely opaque, evergreen wall and is extremely hardy for an evergreen plant. Nevertheless, she occasionally develops into a problem child: She suddenly gets brown scales leaves or shoots and sometimes even completely dies. In the following sections, we will introduce you to the most common causes of brown shoots on Thujas.

winter coloring

If your thuja hedge suddenly assumes a uniform russet hue in winter, that is no cause for concern - it is the normal winter hue of the plants. Bronze foliage in particular shows the wild species Occidental Tree of Life (Thuja occidentalis) and Giant Tree of Life (Thuja plicata). The cultivars 'Brabant', 'Columna' and 'Holstrup' are less discolored, the 'Emerald' variety retains its fresh green color even in heavy frost. The brownish color of the Thujas is an adaptation to the extremely cold and dry winters in their North American homeland.

Road salt and over-fertilization

Thuja, like almost all conifers, is very sensitive to salt. Therefore, Thuja hedges, which are close to a road, often carry damage from road salt in winter. Typical symptoms include browned branch tips near the ground, which are caused by excessive salt concentrations in the soil and in spray water. Incidentally, the thuja also shows similar symptoms if you meant it too well with the blue grain, because mineral fertilizer also increases the salt concentration in the soil water. In case of salt damage, you should first cut back the plants with a hedge trimmer and then rinse thoroughly and water, so that the salt shifts into deeper soil layers.

dryness

All Thuja species and varieties are sensitive to dryness. As is the case with evergreen plants, the symptoms - dried-on, yellow-brown shoots - are delayed and can therefore often no longer be clearly assigned. Thoroughly soak a thuja hedge kept too dry and mulch the soil with bark mulch to prevent it from drying out. In addition, if the soil is too dry, occasionally foliar burns occur after pruning in June in strong sunlight.

Acid soil

On very acidic soils, thuja often shows brownish-black needle staining, which in most cases is responsible for too high a level of free manganese in the soil. Provide the soil first with carbonic lime and two to three months later with mature compost to create a balanced nutrient ratio and to increase the humus content in the long term. Important: Before limescale, it is essential to check the pH value of the soil with a test kit from the garden retailer.

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Dead shoots should be pruned immediately with pruning shears to healthy wood

Leaf and shoot diseases

There are a number of fungal diseases in Thuja that are more or less common. The most common is the so-called Pestalotia dying. The fungus Pestalotiopsis funerea is a weak parasite that characteristically turns the branches inward from the outer tips and causes them to die. On the affected shoots form round, about pinhead-sized, black-brown fruiting bodies that form numerous spores.
Also common is the needle or scaly tan, which is triggered by the fungus Didymascella thujina. Predominantly older leaves shed brownish on their own or in small contiguous areas. In spring appear on the affected scales up to two millimeters large, round to oval, brown-black fruiting bodies. They release spores, which then infect new plants again. Above all, the lower, shadowed branches are affected, since in this area the humidity is higher. A third common disease is Kabatina instinct (Kabatina thujae). The fungus usually only attacks the young, still soft shoot tips and lets them die off.Striking is the sharp demarcation to deeper, healthy branches. Especially plants that grow on very acidic soil and therefore suffer from calcium and magnesium deficiency, are prone to this disease.

Tusk on Thuja

Thuja dandruff (Didymascella thujina)

Most leaf and shoot diseases cause no major damage to the Thuja, if they are detected in time and consistently fought. Cut back on infested plants as far as possible (not down to the old wood!) And treat the plants every two weeks with suitable fungicides such as "Ortiva" or "Duaxo". Since weakened plants are particularly susceptible, you should make sure already during the planting that the soil is sufficiently loose, humus rich and not too dry. A good water and nutrient supply also contributes to the prevention of fungal diseases.

Thuja root rot

Root rot is the most dangerous Thuja disease. The fungus Phytophtora cinnamomi invades Thuja as well as a number of other plant species. It destroys the bark tissue of the plant roots (rhizodermis) up to the root neck. The shoots turn pale pale yellow, later uniformly brown and the plants usually die completely - young Thujas usually within a gardening season. Often in a hedge only individual plants are infected, but the fungus can quickly spread to the neighboring, healthy plants. An indication of a phytophthora infection provides the bark tissue of the root neck: It is no longer cream-colored in Phytophthora infestation, but brownish discolored.

If individual plants in your hedge are infected with the Phytophthora fungus, you should immediately remove them with their root ball and dispose of them with the household waste. A successful control of the disease in the home garden is only possible if you recognize the infection in good time. To combat the fungicide Aliette can be used in the casting process. Before replanting a soil replacement is recommended, because the pathogen can persist in the soil over long periods of spores and usually also infects the new plants. Phytophthora fungi infest mainly plants that are weakened by heavy, compacted soil. Therefore, if necessary, a soil improvement and a good care of the Thuja hedge are the best prevention.

insect infestation

Also different insects may be responsible for brown needles on your thuja. Occasionally, black-eared weevils feed on the bark of the young shoots and ensure that the shoot tips turn brown. The larvae of the Thuja miner's moth (Argyresthia thuiella) feed into the leaf scales, which also leads to the browning of individual shoots. The insects usually do not cause any major damage and can be well controlled by the use of nematodes or a more frequent pruning (miner moth).
In contrast, a problem with the thuja bark beetle (phloeosinus) is problematic because it can damage the bark tissue so severely that the plants enter. Small holes in the trunk are a sure sign of the pest. As a precaution, you should excavate, chop and dispose of severely affected plants or plant parts. At the same time, look for the other Thujas in your hedge to symptoms of symptoms such as single yellowed shoots. If possible, dispose of infested wood in winter, as this will eliminate the wintering bark beetle.

Video Board: How to grow Green Giant Thuja (Arborvitae) with detailed description.

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