Eucalyptus is widely used as a street tree in urban areas and for garden landscaping. Known for its elegant shape, lush green foliage, and evergreen nature, it's a popular choice for many landscapes. However, eucalyptus trees are sensitive to alkaline conditions, have poor cold tolerance, and are prone to various pests and diseases. One of the most common issues they face is yellowing disease, also known as chlorosis.
Yellowing disease is a physiological condition that occurs when eucalyptus trees grow in alkaline soils. These trees prefer acidic soil, and prolonged exposure to alkaline conditions can hinder their ability to absorb essential nutrients like iron. This deficiency leads to yellowing of the leaves, which is essentially a sign of iron deficiency. In northern China, where most soils are alkaline, eucalyptus trees are particularly vulnerable to this issue. Additionally, with the expansion of urban development and the transformation of old cities, construction debris and harmful substances have been introduced into the soil, altering the natural growing environment for eucalyptus. This further contributes to the occurrence of yellowing disease.
The symptoms of eucalyptus yellowing disease typically start at the top of the tree, with new leaves showing more severe damage than older ones. The leaves gradually turn yellow, develop white or pale spots, and the veins become very light green. In severe cases, the leaves may become completely pale, with some parts turning necrotic. The condition tends to worsen during winter and spring, making it more noticeable in these seasons.
To manage yellowing disease, it's important to adjust the soil pH and increase the availability of iron. One approach is to apply sulfur powder to the soil, which helps lower the pH. Another method is to pour a diluted ferrous sulfate solution (1:20) around the roots. For more severe cases, trunk injections can be effective—mixing 15 grams of ferrous sulfate, 50 grams of urea, and 5 grams of magnesium sulfate in 1 liter of water and injecting it into the trunk. Foliar sprays using a 0.1–0.2% ferrous sulfate solution can also help improve leaf color and overall health. Regular monitoring and timely intervention are key to maintaining healthy eucalyptus trees in urban and garden settings.
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