Ginkgo Bark

Botanical Information

Botanical Classification

Ginkgo, a plant of the Ginkgoaceae family.

Morphological Characteristics

A deciduous large tree with a breast height diameter of up to 4 meters; the bark of young trees is nearly smooth and light gray, while that of mature trees is gray-brown, irregularly fissured longitudinally, and rough; it has long branches and slow-growing, spur-like short branches. The crown of young and middle-aged trees is conical, becoming broadly ovate with age; branches are nearly whorled and extend obliquely upward (the large branches of female trees are often more spreading than those of male trees).Leaves are alternate, arranged in a radiate pattern on long branches; they have slender petioles, are fan-shaped, and are pale green and glabrous on both surfaces. They are scattered on long branches and clustered on short branches. The venation pattern is “dichotomous.” On long branches, the leaves are often bifid, with a broadly wedge-shaped base.The plant is dioecious, with unisexual spherical flowers arising in clusters from the axils of scale-like leaves at the tips of short branches. It blooms in April and matures in October; the seeds have long stalks and hang downward, typically being elliptical, oblong-obovate, ovoid, or nearly spherical. The seed coat is fleshy and covered with a white powder; the outer seed coat is fleshy and turns yellow or orange-yellow when ripe.

Distribution Area

It is primarily distributed in Shandong, Jiangsu, Sichuan, Hebei, Hubei, Henan, Gansu, and other regions. The largest ginkgo cultivation base in China is located in Tancheng County, Shandong Province.

Growth Habits

It thrives in subtropical monsoon regions with favorable water and heat conditions. The soil is yellow soil or yellow-brown soil, with a pH of 5–6.

Propagation Methods

1. Propagation by Cuttings Propagation by cuttings can be divided into hardwood cuttings and softwood cuttings. Hardwood cuttings are suitable for propagating seedlings for large-scale landscaping, while softwood cuttings are suitable for propagating small quantities of seedlings for home or landscaping use.Mature-branch cuttings are typically taken in the spring, from March to April. High-quality branches that are 1 to 2 years old are selected from established nurseries or mature trees, then cut into 15–20 cm long cuttings. The upper cut should be smooth and rounded, while the lower cut should be made in a “horse-ear” shape.After cutting, bundle the cuttings in groups of 50, rinse them thoroughly with clean water, then soak them in a 100 ppm solution of ABT rooting powder for 1 hour before planting them in fine yellow sand or loose seedbed soil. Water thoroughly after planting and keep the soil moist; roots will form in about 40 days. Once established, provide normal care, and the seedlings can be transplanted in the following spring.Softwood cuttings are taken from late May to mid-June. Cut non-lignified shoots from around the Ginkgo root zone or from branches that have produced panicles but have not yet lignified (cuttings should be about 2 cm long, with 2 leaves left attached). Place the cuttings in a container and position them in diffused light, changing the water approximately every 3 days until callus tissue forms. They can then be transplanted into fine yellow sand or nursery bed soil; however, shade must be provided around noon on sunny days,Spray the foliage 2 to 3 times, and once the cuttings have taken root, resume normal care. 2. Division Propagation Division propagation is generally used to produce rootstocks and seedlings for landscaping. Ginkgo trees readily produce suckers, with trees aged 10 to 20 years producing the most.In spring, Ginkgo biloba can be propagated by division using these suckers. The method involves removing the soil around the root collar, cutting the sucker with fibrous roots from the mother plant with a knife, and planting it separately for cultivation. Suckers from female trees can accelerate the onset of fruiting. 3. Grafting Grafting is primarily used in fruit production. Greenwood grafting can be performed from late May through early August; however, it should not be carried out during periods of high temperatures and drought, especially at midday on sunny days, and should also be avoided on rainy days.The specific method is as follows: First, collect vigorous, multi-year-old branches from a high-quality ginkgo mother plant. Trim one leaf from the scion, leaving only the petiole, and cut a segment containing 2 to 3 buds. Then, dip the lower end of the scion into water or wrap it in a damp cloth; it is best to graft immediately after collection. Rootstocks can be selected from 2- to 3-year-old seedlings grown from seed or cuttings.For early-bearing, high-density plantings, the grafting position should be around 1 meter. For All-Red Poplar, cleft grafting or side grafting is generally used. The cut surface of the scion should face inward and be inserted into the rootstock’s cut, ensuring the two fit together with the cambium layers aligned. Secure the graft with a plastic tape, and the tree will begin bearing fruit 5 to 8 years after grafting. 4. Propagation by Seed Propagation by seed is primarily used for large-scale landscaping or for creating clump-style bonsai. After harvesting seeds in the fall, remove the outer seed coat and sun-dry the seeds with their fruit peel intact; they can be sown in winter of the same year or in the following spring. If sowing in the spring, germination must first be induced through stratification in sand.When sowing, place the seed embryo horizontally in the sowing furrow. Cover with 3–4 cm of soil and firm it down; seedlings can grow to 15–25 cm in height within the same year. After the Red Poplar loses its leaves in the fall, the seedlings can be transplanted. However, it is important to select a seedbed in a well-drained area to prevent waterlogging, which can cause the parts of the seedlings near the ground to rot.

Cultivation Techniques

1. Site Selection

Ginkgo trees have a long lifespan, and a single planting provides long-term benefits; therefore, site selection is critical. As a sun-loving species, ginkgo should be planted on sunny slopes with gentle gradients. While not particularly demanding regarding soil conditions, it thrives best in neutral or slightly acidic soils that are deep, moist, fertile, and well-drained.

2. Planting

(1) Proper Placement of Pollinator Trees

Ginkgo is a dioecious plant; to achieve high yields, pollinator trees must be appropriately arranged. Select male trees that match the female variety and have the same flowering period, with a male-to-female ratio of 25–50:1. The arrangement can follow a square center pattern with 5 or 7 trees, or a four-corner configuration.

(2) Optimal Planting Density

Ginkgo grows relatively slowly in its early stages; dense planting can improve land utilization and increase yield per unit area.Typically, plant spacing of 2.5 × 3 m or 3 × 3.5 m is used, with 88 or 63 trees planted per mu. After the rows have closed, transplant the trees by removing every other row to create a spacing of 5 × 3 m or 6 × 3 m, resulting in 44 or 31 trees per mu. Every few years, repeat this process by removing every other row from the original spacing to achieve a spacing of 5 × 6 m or 6 × 7 m,resulting in 22 or 16 trees per mu.

(3) Seedling Specifications

High-quality, vigorous seedlings are the foundation for early fruiting and high yields in ginkgo. Select seedlings with a height-to-diameter ratio of 50:1 or higher, a taproot length of 30 cm, well-developed lateral roots, and new shoot growth of at least 30 cm in the current year for planting.In addition, seedlings must have a vigorous terminal bud, plump and well-developed lateral buds, and be free of pests and diseases.

(4) Planting Time

Ginkgo is primarily planted in the fall while the leaves are still on the tree or in the spring before leaf emergence. Fall planting takes place from October to November, allowing the seedling’s root system a longer recovery period and preparing it for above-ground bud break the following spring.Planting in the spring before bud break results in poorer growth compared to fall planting, as the above-ground parts sprout quickly, leaving the root system insufficient time to recover.

(5) Planting Method

For ginkgo planting, dig planting holes according to the designed spacing between rows and plants, with dimensions of 0.5–0.8 × 0.6–0.8 meters. After digging the holes, backfill with topsoil and apply fermented fertilizer containing superphosphate.During planting, spread the seedling’s roots naturally, align it with neighboring seedlings in all directions, and then backfill with topsoil while firming it down. The optimal planting depth is when the backfilled soil reaches 2–3 cm above the seedling’s original soil mark; do not bury the seedling too deeply. Water the seedlings promptly after planting to improve survival rates.

Pest and Disease Control

Stem Rot

1. Distribution and Damage: This disease is widespread in all ginkgo seedling propagation areas. It most commonly affects 1- to 2-year-old ginkgo seedlings, with 1-year-old seedlings being particularly severely affected, often resulting in mass seedling mortality.

2. Symptoms: In the early stages of infection, the base of the seedling turns brown, the leaves lose their normal green color and droop slightly, but do not fall off.The infection rapidly spreads upward, eventually causing the entire plant to die. The bark at the base of infected seedlings becomes shriveled; the inner tissue rots, taking on a spongy or powdery texture, turning grayish-white and containing numerous tiny black sclerotia. The pathogen can also invade the xylem of the seedlings, so small sclerotia are sometimes observed within the brown, hollow pith.The pathogen subsequently spreads to the roots, causing the root cortex to rot. If a diseased seedling is pulled out by hand, only the xylem is removed, while the root cortex remains in the soil. Stem rot can also occur in ginkgo cuttings under high or low temperature conditions, causing the cuticle of the cutting to form a tubular sheath around the xylem, while the phloem parenchyma turns completely black and rots.

3. Pathogen: The pathogen responsible for ginkgo stem rot is the charcoal rot fungus Macrophomia phasoli (Maubl.) Ashby, belonging to the order Sphaerocarpales, family Sphaerocarpaceae, and genus Macrophomia. This fungus thrives in high temperatures, with an optimal growth temperature of 30–32°C; it is not particularly sensitive to pH and can grow well within a range of pH 4–9.

4. Disease Development: The stem rot pathogen typically lives saprophytically in the soil and is classified as a weakly parasitic fungus. Under favorable conditions, it invades through wounds on the seedlings. Therefore, the occurrence of the disease is related to the host and site conditions. The fundamental cause of damage to seedlings is excessive surface soil temperature, which causes heat scorch at the base of the seedlings, allowing the pathogen to invade. The lower the degree of lignification in the seedlings, the higher the incidence of this disease.The incidence rate also increases significantly when water accumulates in low-lying areas of the seedbed. For Ginkgo cuttings, when seedbed temperatures reach 30°C or higher between June and August, symptoms begin to appear 10–15 days after planting; in severe cases, large areas of scions turn black and die. Experiments have shown that antagonistic actinomycetes can effectively inhibit the spread of the pathogen.

5. Control Methods: Based on the causes of ginkgo stem rot, prevention should be the primary focus.

(1) Early sowing: Aim to sow as soon as the soil thaws. This measure promotes early lignification of the seedlings, enhancing their resistance to high surface soil temperatures.

(2) Appropriate sowing density: Dense sowing helps leverage the collective effect of the seedlings, strengthening their resistance to adverse environmental conditions.Experiments have shown that the lower the seedling density, the higher the incidence rate; conversely, the higher the density, the lower the incidence rate. Practice has also demonstrated that when the seeding rate was increased from 25–40 kg per mu to 80–100 kg per mu, not only did the incidence rate decrease, but the yield per unit area also increased, thereby conserving land and reducing disease incidence.

(3) Control of Soil-Borne Pests: Seedlings damaged by soil-borne pests are highly susceptible to infection by stem rot pathogens; therefore, it is essential to pay constant attention to eliminating soil-borne pests before and after sowing.

(4) Prevention of Mechanical Damage to Seedlings: When loosening soil, weeding, or transplanting seedlings—whether from the current year’s sowing or one-year-old transplants—care must be taken not to damage the roots or stems, as this can easily lead to the occurrence of stem rot.

(5) Shading and Cooling: To prevent soil temperatures from rising due to solar radiation, measures such as erecting shade structures, mulching between rows, planting corn, or using branches for shade should be taken in the nursery to reduce harm to the seedlings.

(6) Irrigation and Spraying: During hot seasons, timely irrigation and spraying should be carried out to lower surface temperatures. Where conditions permit, sprinkler irrigation is recommended, as it is more effective in reducing the incidence of disease.

(7) Chemical and Biological Control: In conjunction with irrigation, various fungicides such as Topsin, Carbendazim, and Bordeaux mixture can be sprayed. Alternatively, antagonistic actinomycetes can be added when applying organic fertilizer in mid-June, or wood ash/superphosphate (1:0.25) mixed with antagonistic actinomycetes can be applied as a top dressing.

Leaf Blight

(1) Distribution and Damage:This disease occurs to varying degrees in major ginkgo-producing regions such as Guangxi, Zhejiang, Jiangsu, and Shandong. Generally, incidence is more severe in established production areas than in newer ones. Reports indicate that ginkgo trees cultivated near Metasequoia trees exhibit significantly more severe symptoms, and the incidence rate is higher in female trees than in male trees. In mild cases, some leaves wither and fall prematurely; in severe cases, all leaves are shed, leading to weakened tree vigor and stunted growth and development.

(2) Symptoms: In the early stages of the disease, yellowing of the leaf tips is common. Around June, the yellowed areas gradually turn brown and die off, spreading from localized spots to the entire leaf margin, forming brown to reddish-brown marginal lesions. Subsequently, the lesions gradually spread toward the base of the leaf until the entire leaf turns brown or grayish-brown, withers, and falls off.From July to August, the boundary between diseased and healthy tissue is distinct; the margins of the lesions are wavy and darker in color, with a narrow or wide band of bright yellow visible along the outer edge. Beginning in September, the lesions enlarge significantly, their spreading margins become irregular, and the boundary between diseased and healthy tissue gradually becomes indistinct.In addition, from September to October, leaves on shoots sprouting from the base of seedlings or mature trees develop several irregular, discolored spots at random locations, with brown centers. Although these spots do not expand significantly, they often merge with the spreading marginal lesions.

(3) Pathogens: The pathogens responsible for ginkgo leaf blight are relatively complex. According to research, at least three pathogens have been identified: Alternaria alternata (Fr.) Keissl, Glomerella tacingulate (Stonem) Spauld. et Schrenk, and Pestalotis ginkgohori.In addition, fruiting bodies of various fungi, such as Alternaria, Colletotrichum, Pestalotia, and Trichoderma, can be observed on the lesions.

(4) Relationship Between Disease Incidence and Environmental Factors: Observations have shown that mature trees are more resistant to the disease than seedlings, and the incidence rate in female trees increases significantly as fruit yield rises.Furthermore, waterlogging at the roots, leading to root rot or weakened tree vigor, can result in earlier and more severe disease onset. Generally, trees fertilized with base fertilizer show milder symptoms than those receiving topdressing; the incidence rate is lower for trees fertilized in winter than in spring. The disease is milder when ginkgo is intercropped with soybeans but more severe when intercropped with pine trees; incidence is severe near Metasequoia trees but milder at a distance. This may be related to the fact that the pathogen causing this disease is the same as that affecting the intercropped tree species(such as Metasequoia red rot).

(5) Control Measures: ① Strengthen management to enhance tree vigor. For example, aim to apply fertilizer in winter, avoid waterlogging, eliminate intercropping with pine and Metasequoia, improve the quality of seedling planting, and shorten the acclimatization period to enhance the seedlings’ disease resistance. Additionally, control excessive fruiting on female trees to prevent the spread of this disease in mature ginkgo trees.② Chemical control: Spray broad-spectrum fungicides such as Topsin-M before the onset of disease. Alternatively, starting in early June, spray a 500-fold dilution of 40% Carbendazim suspension concentrate or a 1,000-fold dilution of 90% Propiconazole, repeating every 20 days for a total of six applications, which can effectively prevent the occurrence of this disease.Early Yellowing Disease (1) Distribution and Damage: This disease occurs to varying degrees in all major ginkgo-producing regions. Furthermore, yellowed plants are more susceptible to leaf blight, leading to premature defoliation and a significant slowdown in height and girth growth. Seed yield decreases, and in severe cases, the entire plant may die. (2) Symptoms: In Shandong and Jiangsu provinces, this disease typically appears around early June, mostly in scattered outbreaks.From late June through July, the number of yellowed plants gradually increases, forming small patches. In mild cases, only the tips of the leaves turn a bright yellow; in severe cases, the entire leaf turns yellow. This early leaf yellowing also leads to the premature onset of ginkgo leaf blight; by August, the entire leaf turns brown, withers, and falls off in large numbers.(3) Pathogenicity Studies suggest that early yellowing disease in ginkgo is caused by abiotic factors. The primary causes of the disease include: water deficiency, damage from soil-dwelling pests, waterlogged soil, root damage during seedling lifting or planting, and zinc deficiency in the soil.(4) Control Measures: ① Apply Multi-Effect Zinc: Applying 141 g of Multi-Effect Zinc per seedling in late May can reduce the incidence rate by 95% and significantly lower the disease index. ② Promptly control soil-dwelling pests such as wireworms, mole crickets, and golden wireworms. ③ Prevent waterlogging, increase soil aeration through loosening and weeding, and improve soil permeability.④ Protect seedlings from damage; prevent root damage and improper planting during transplantation. ⑤ Irrigate at appropriate times to prevent severe drought. Ginkgo Wilt (1) Distribution and Damage: Also known as Ginkgo stem rot, this disease is found in Hebei, Henan, Shaanxi, Shandong, Jiangsu, Zhejiang, Jiangxi, and Guangxi provinces (autonomous regions). In addition to ginkgo, it also affects tree species such as chestnut.The disease occurs on the main trunk and branches. Once infected, lesions rapidly encircle the branches and trunk, often resulting in the death of the entire branch or the whole tree. (2) Symptoms: After the pathogen enters the main trunk or branches through wounds, it produces discolored lesions on smooth bark. These lesions are round or irregular in shape; on rough bark, the edges of the lesions are indistinct.The lesions continue to expand and gradually swell, causing the bark to crack longitudinally. In spring, numerous withered, yellow, wart-like fruiting bodies, 1–3 mm in diameter, can be seen on the affected bark. During humid weather, pale yellow or yellow, tendril-like conidial horns can be squeezed out from these wart-like fruiting bodies. After autumn, the fruiting bodies turn orange-red to dark reddish-brown. Subsequently, ascomata gradually form.A feathery, fan-shaped mycelial layer is visible between the bark and xylem of diseased trees; it is initially off-white and later turns yellowish-brown. Ginkgo (3) Pathogen: The pathogen responsible for Ginkgo dieback is the chestnut blight fungus (4), belonging to the genus Endocystis within the order Sphaerocystales of the class Ascomycetes. Disease Progression: Both the conidia and ascospores of the pathogen can cause infection.The fungus overwinters on diseased branches as mycelium and conidiophores; it becomes active when temperatures rise the following spring. In the Yangtze River Basin and areas south of the Yangtze River, symptoms begin to appear from late March to early April; lesions expand significantly after late June, with the fastest expansion occurring between July and September. In the Yangtze River Basin, the asexual stage of the pathogen begins to appear from late April to early May.Conidia are dispersed by rain, insects, and birds, enabling repeated re-infections. From October to November, orange-red asci embedded in the ascocarps appear on the bark; ascospores mature in early December. Ascospores are dispersed by wind and invade the host through wounds.The fan-shaped mycelial layer beneath the bark of infected trees is highly resistant to adverse environmental conditions and can survive the winter. (5) Control Methods: ① Since the pathogen is a weak parasite, infection occurs only when the tree is severely weakened. Therefore, proper management should be implemented to strengthen the tree’s vigor and reduce the incidence of the disease. ② Thoroughly remove diseased trees and branches; infected branches should be burned promptly.③ Chemical control. For isolated lesions on the trunk or branches, scrape away the affected tissue and disinfect the wound promptly. Scrape the bark down to the xylem, then apply a 0.1% HgCl₂ solution or Shengping solution (0.5 liters of mercury + 0.2% Pingpingjia + 97.5 liters of water) to the wound to kill the pathogen.After scraping, apply a 400–500-fold dilution of Antibacterial Agent 401 mixed with 0.1% Pingpingjia to the wound; alternatively, applying the fungicide methyl thiophanate or a 10% alkaline solution to the wound also yields good results.