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Powdery mildew is a common disease that affects young seedlings in nurseries. It typically occurs under high temperature and humidity conditions, especially when the seedlings are densely packed and ventilation is poor. The symptoms first appear as gray-brown spots along the main veins on the underside of young leaves, which then spread across the entire leaf surface. A white powdery layer can also be seen on severely affected shoots and stems. To manage this disease, it's important to maintain good sanitation in the nursery, thin out the seedlings, and promptly remove or burn any infected plants. Additionally, applying a 0.3–0.5° solution of lime sulfur at intervals of 10 days, for three to four applications, can effectively control the infection. Black spot disease commonly affects eucalyptus seedlings after they have developed 1 to 4 leaves. The disease causes the tips of the shoots to turn dark brown and eventually die. Prevention starts with disinfecting seeds, soil, and coverings before sowing. When the disease appears, infected seedlings should be removed immediately, and the area should be treated with 0.5% potassium permanganate or formalin to prevent further spread. Alfalfa weevil is another pest that can cause significant damage to one-year-old eucalyptus seedlings, leading to severe mortality. Once trees are established, adult weevils feed on the upper canopy leaves, which can hinder tree growth. Control measures include spraying seedlings with 0.5 kg of Yanghua flower or Tripterygium powder mixed with 75–100 liters of water. Alternatively, 90% trichlorfon or 50% marathon emulsion diluted at 2000 times can be used for effective control. The leaf roller moth is a recurring pest that attacks eucalyptus shoots through its larvae, affecting the tree's growth and causing bending or drying of new shoots. During January and March, when new shoots emerge, the first generation of larvae can be controlled by spraying 90% trichlorfon, 50% dibromophosphorus emulsion, or 50% marathon emulsion diluted at 10,000 times, repeated every five days for two to three applications. If larvae have already invaded new shoots, 40% dimethoate emulsion diluted at 200–300 times can be used. In smaller nurseries or forest areas, burning winter litter can help eliminate overwintering pests. Fruit pod borer is a serious threat to eucalyptus seedlings and saplings under 20 years old, with two generations per year. The first generation of larvae is active from late May to mid-July, while the second generation appears in August and September. These larvae feed on shoots and roll leaves into bulbous shapes, damaging terminal buds and even killing new shoots or entire plants. Early intervention is key—when larvae have not yet formed nests, spraying 90% trichlorfon diluted at 4000–5000 times can kill them. If nests are already formed, it's best to cut and burn the infested branches. Hao Tianniu (a type of longicorn beetle) lays eggs during the adult spawning period, which runs from early May to early June. During this time, adults lay eggs or newly hatched larvae can be found near the base of the tree. Infested branches can be manually cut and treated by injecting dichlorvos or similar agents into the entry holes to kill the larvae.

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