Osmanthus breeding techniques and pest control
Osmanthus fragrans is a distinctive ornamental plant native to China, widely used in garden design. It is often integrated with buildings, hills, and rocks, creating harmonious landscapes. Tufted shrubs are commonly planted near pavilions, buildings, and house corners, while also appearing scattered or grouped in parks and gardens, adding fragrance and visual appeal.
Propagation of Osmanthus can be done through several methods, including cutting, layering, grafting, and sowing. Among these, cuttings are the most frequently used technique due to its high success rate and ease of implementation.
Cutting is typically performed between June and July or September and October. Semi-woody branches from the current year, especially the top ones, are ideal for this process. After planting, it's essential to provide timely shade, regular watering, and proper fertilization. Rooting usually begins within 20 days, and full rooting takes about 30–40 days. In winter, protection against cold is necessary. By the following year, the seedlings can reach a height of approximately 30 cm.
Layering involves two main types: aerial layering (high pressure) and ground layering. Aerial layering is best done in early April, while ground layering is suitable for early April or during the rainy season. Both methods require wounding or ring-barking the branch before it is separated from the parent plant after one year. The layer should be buried about 4–5 cm deep, and the bent part in the soil helps promote root development.
Grafting is usually carried out from March to April. Common rootstocks include Ligustrum lucidum and Ligustrum japonicum. Techniques such as cleft grafting, whip grafting, and splice grafting are commonly used. When grafting, it’s important to keep the scion and rootstock moist. The graft union should be as low as possible, and the rootstock should be cut 3 cm above the ground. After wrapping the area with soil, the scion can develop roots, improving the survival rate.
Sowing is typically done in winter or early spring. Seeds are sown in rows spaced 15–20 cm apart, with 30–40 seeds per meter. The recommended sowing rate is 8–10 kg per acre. The seeds are covered with a thin layer of humus or fire soil, about 1.5 cm thick, and then topped with grass. Germination usually starts 40–50 days after sowing and lasts 50–60 days. Seedlings may not emerge uniformly. From July to September, when growth is vigorous, additional fertilizer and drought resistance measures are needed. Seedlings reaching over 30 cm in height can be transplanted from the nursery.
When transplanting seedlings, care should be taken to preserve the root system. They should be planted immediately after emergence. If long-distance transport is required, moisture must be maintained to prevent damage.
Pest and disease control is crucial for healthy growth. Common pests include scale insects, which can be managed by scraping them off manually, applying 5% oil emulsion or 5° lime sulfur before bud break, and spraying malathion or imidacloprid solutions when the scales are young.
Another common issue is the starry smudge, which affects buds, leaves, and flowers, causing discoloration and wilting. Spraying 3–5° lime sulfur before sprouting or 0.3–0.5° lime sulfur before flowering can help manage this problem.
Leaf spot disease causes severe leaf loss, especially under high humidity and temperature. Applying 80% mancozeb WP at a rate of 0.5 kg per 250–300 liters of water before flowering, and using a 1:1:100 Bordeaux mixture during the growing season, can effectively control the spread of the disease.
Root rot disease affects the trunk and large branches. Preventive measures include proper fertilization and irrigation to strengthen the tree. Early detection and treatment are essential. Scraping the affected areas and applying a 5° lime sulfur mixture in early spring or autumn can significantly improve recovery.
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