1, the main pathogenic fungi are Alternaria alternata, which can infect ginkgo trees and cause leaf blight, and can infect both leaf orchards and old fruit trees. June is the initial period of onset, and July-September is the peak period of onset. The symptom is that the initial leaf edge turns yellow, and then turns into a reddish-brown leaf edge lesion, which is wavy. At the initial stage, the junction between disease and health is obvious, and sometimes there are bright yellow lines with different widths on the outer edge, and then the lesion gradually extends inward, making the junction between disease and health blurred until the whole leaf turns brown, grayish brown and withered. This bacterium can also harm poplar, cypress and Metasequoia.
2. The main pest causing the yellowing of Ginkgo biloba leaves is tea thrips, belonging to thyme wing thrips, which can damage from April to September and reach its peak in the middle and late July. In southern Shandong and northern Jiangsu, thrips Camellia occurred for 4 generations in 1 year (1 generation from late April to early June; The second generation from mid-June to mid-July; The third generation is from late July to mid-August; The fourth generation occurs from late August to early September), with the first and second instar nymphs as the damage and pupae overwintering in the soil. File suction device mainly harms the new shoots and leaves of seedlings and mature trees. They often gather on the back of leaves to suck juice. After drying, the leaves appear silvery white spots, which gradually turn into yellowish brown spots, and the leaves become thick, uneven or slightly curled forward. In severe cases, the leaves are dry and broken, leading to early defoliation. In addition, underground pests bite the bark of seedlings, which is easy to cause yellow leaves.
3. The yellowing of leaves is caused by lack of fertilizer or unreasonable fertilization. Lack of fertilizer, such as lack of nitrogen, leaves are yellow, dull and small. Without phosphorus, the old leaves turn into yellow-green flowers with purple or red spots on them. Lack of potassium, the leaves at the base or middle of new branches turn yellow, stop growing early, and brown spots appear at the tip or edge of leaves. In severe cases, the leaves will scorch from the outside to the inside. Calcium deficiency, brown-green or brown necrotic spots on leaves. Magnesium deficiency, basal leaves fade and fall off, and a small number of thin light green or yellowish brown leaves remain at the top. Under the condition of sulfur deficiency, young leaves first turn green and yellow, and then mesophyll turns yellow. In severe cases, reddish-brown focal spots often appear at the base of leaves. Iron deficiency causes new leaves to turn yellow. Without manganese, the early leaf margin changed from green to yellow-green, then the whole leaf turned yellow-green, and brown spots appeared on the leaf margin. Boron deficiency, new leaves are small, old leaves shrink and turn yellow, and the edges are brown and curly. Lack of copper, thin plants, green and yellow leaves, deformity, dryness and loss. Lack of molybdenum, light leaf color, yellow tip. Zinc deficiency, small leaves and green veins. In addition, unreasonable fertilization, such as excessive fertilization, or only nitrogen fertilizer without organic fertilizer, leads to yellowing.
4. Yellow water includes drought yellow and waterlogging yellow.
Drought and yellow: the soil water supply is insufficient to meet the growth and development needs of ginkgo trees, resulting in weak or wilting leaves and yellow edges, resulting in early defoliation. According to the experiment, the yellowness of the leaf-picking nursery of 3-5-year-old seedlings is smaller when watered from mid-May to mid-June, and the yellowness of watering twice is smaller than that of watering 1 time. Waterlogging yellow: poor drainage in ginkgo orchards and water accumulation in soil lead to long-term anaerobic respiration of roots, excessive alcohol accumulation and root poisoning. Or the soil is hardened and the ventilation is not smooth, resulting in yellowing of the leaves. The results showed that the yellow leaves of flooded ginkgo seedlings were heavier than those of flooded ginkgo fields within 5 days, and the soil compaction was heavier than that of loose yellow leaves.
5. Dense yellow refers to the over-dense planting of ginkgo leaf-picking nursery, which has poor ventilation and light transmission, and the plants compete for fertilizer, water and shade, which affects photosynthesis, consumes a lot of breath and is vulnerable to the harm of tea thrips, leading to yellow leaves and early defoliation. For example, the dense part of the leaf picking garden is heavier than the sparse part of yellow leaves, and the inner room is heavier than the peripheral yellow leaves.
6. The yellow field caused by improper management. For example, the roots are damaged when seedlings are raised, nested when planted, animals bite branches or artificially damage the skin, resulting in yellowing of leaves.