Yellow spots on thuja

Yellow spots on thuja

Yellow spots on thuja - causes and rescue measures for the hedge

Tuyata (especially the varieties Thuja occidentalis 'Smaragd’ and 'Brabant') is the most used evergreen plant for building dense hedges in Bulgaria. When they are healthy, thuja form a perfect emerald wall. However, very often the owners face an unpleasant surprise: the appearance of yellow, brown or black spots on branches, which quickly grow and lead to partial or complete drying of the plant.

The massive mistake at this point is panicked and indiscriminate watering or buying random fertilizer. Yellow spots are just a symptom – they can be caused by a fungal infection, pest attack, watering mistakes or pets. Here's how to perform a quick diagnosis and what rescue measures to take right away.

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Fungal diseases (Didimela and Kabatina)

If the yellowing starts from the tips of the young twigs and gradually turns brown, and along the transition between healthy and diseased tissue, small black dots are visible, it is most likely a fungal infection. These fungi thrive best in warm, humid weather (frequent spring rains, combined with high temperatures) or in densely planted plants with poor air circulation.

  • Rescue measure: Cut all badly affected and withered branches with disinfected scissors and burn them (do not throw them in the compost!). Treat the entire hedge with a professional fungicide (for example Topsin M, Skor or Switch) at least twice in 10-14 days.

Pest attack: Mites and thuja scale louse

If the yellowing of thuja is accompanied by fine, barely noticeable cobwebs on the inside of the branches, and the leaves appear grayish-brown and lifeless, your hedge is attacked by red spider mite. These microscopic pests suck sap from the needles and literally dry up the plant for a season.

  • Rescue measure: Spray the inside of the crown liberally and deeply with a specialized acaricide (for example Masai, Sanmayt or Nisoran). The shield louse can be recognized by the small brown "shields" on the stems - a systemic insecticide is used against it.

Black spots at the base: The influence of dog urine

If the spots on thuja are located entirely in the lower part of the plants (to 50-60 cm from the ground) and are deep black, charcoal color, the problem is not biological.

  • The reason: This is clearly the result of male dogs or cats urinating on the plant. Pet urine contains an extremely high concentration of nitrogen and salts, which literally “they burn” the delicate tissue of thuja.
  • Rescue measure: Immediately wash the area thoroughly with clean water, if it is fresh. The only permanent way of salvation is to install a low decorative fence or mesh, which physically stops animals from accessing the trunk.

Physiological stress: Watering errors and dry air

Withering of thuja is often due to both extremes in maintenance:

  • Water shortage: Newly planted thuja have a shallow baled root system. If the drip hose does not run regularly in the summer, they dry from the inside out.
  • Overwatering and swamping: If the soil is heavy and clayey, and the drip works without stopping, thuja roots rot from lack of oxygen. The plant begins to yellow massively, as the damaged root stops feeding the crown.

Frequently asked questions

1. Is it normal for thuja to turn brown deep on the trunk in the fall??
Yes, it's completely normal. This process is called “autumn cleaning” or internal exposure. The thuja is replacing its old needles (of age 3-5 years), which are deep in the crown and have no access to light. In the spring, just clean these dry parts with a glove.

2. Can we save this one?, which has turned yellow on 80%?
If most of the crown is completely dry, brittle and brown, the root is probably dead and the plant cannot be saved. The most pragmatic solution is to replace it with a new one.

3. What fertilizer to use to restore yellowed thuja?
Use specialized mineral fertilizers for coniferous plants, which contain a high amount of **Magnesium ($Mg$)**. Magnesium is a key element for photosynthesis in conifers and quickly restores the rich green color of the crown.

Conclusion

The problem of the drying of thuja and the appearance of yellow spots requires a quick response. Don't wait for the spots to cover the entire hedge. Make a correct diagnosis - whether it is a fungus, mites or wrong watering – and apply the right detergent. With regular prophylaxis, proper magnesium fertilization and controlled drip irrigation, your hedge will stay thick, healthy and impeccably green.

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