How to prevent and control pests and diseases in the Chinese medicinal herb ginseng?
Diseases
Damping-off: Rhizoctonia solani Kuhn. The pathogen is a type of fungus belonging to the Deuteromycetes. Also known as "soil collar rot." This disease mainly occurs during the seedling emergence and leaf unfolding stage. Ginseng aged 1 to 3 years is severely affected; the affected seedlings show brown ring-like constriction at the stem at the boundary between dry and wet soil below the soil surface, and the seedlings collapse and die.
Control methods: Before sowing, treat the soil with 3 kg of 50% carbendazim per mu; in the early stage of disease, irrigate the affected area with a 1000-fold dilution of 50% carbendazim to a depth of about 4 to 5 cm, then rinse the ginseng leaves with clean water; immediately remove and burn diseased plants, and disinfect the diseased holes with 5% lime milk or similar; strengthen field management, keep the seedbed well ventilated, and avoid excessive soil moisture.
Bacterial soft rot: It mainly damages the roots. The lesions are brown and soft-rotted, with clear edges, round to irregular in shape, varying in size, often several merging together, and eventually causing the entire ginseng root to become soft-rotted. When the lesion is squeezed by hand, white bacterial ooze exudes, with a strong pungent odor. In severe cases, the entire ginseng root tissue rots and disintegrates. In the early stage, the aboveground part of the plant shows yellowing at the leaf margins and slight upward curling; irregular brownish-yellow or red spots appear on the leaves. In severe cases, the entire leaf turns purplish-red, and finally the leaves wilt. The wilting progresses from reversible to irreversible.
Pathogens: The pathogens are two species of bacteria: (1) Pseudomonas caryophylli Starr et Burkholder, belonging to the genus Pseudomonas. The cells are rod-shaped, without capsules, with polar flagella, and Gram-negative. (2) Erwinia carotovora var. carotovora Bya., belonging to the genus Erwinia. The cells are short rod-shaped, with peritrichous flagella, and Gram-negative.
Disease pattern: Ginseng soft rot bacteria exist in large quantities in the soil, and the soil is the overwintering site and primary infection source of the soft rot bacteria. The bacteria mainly invade the ginseng root through wounds. When the ginseng root grows vigorously and has strong disease resistance, the pathogen remains in a latent state. All parts of the ginseng root can serve as latent sites for the soft rot pathogen, with the highest bacterial carriage rate in the buds. When the ginseng root grows weakly and its disease resistance decreases, or when external temperature and humidity conditions are suitable, soft rot symptoms appear on the ginseng root. In the late stage of the disease, it often co-infects with fungi such as Fusarium and Rhizoctonia, and fungal mycelium appears outside the lesions.
Control measures: (1) Choose high, dry plots for planting ginseng to prevent soil compaction and water accumulation; do not use seed roots with wounds, and prevent ginseng roots from being injured during transplanting. (2) Strengthen cultivation management, provide timely cold protection in winter, and pay attention to controlling underground pests to reduce wounds. (3) Soil disinfection: broadcast and mix 50 g of 20% copper acetate wettable powder per curtain; spray with a 1000- to 2000-fold dilution of 80% ethylicin emulsifiable concentrate; use a 1000-fold dilution of 50% chlorobromoisocyanuric acid water-soluble powder, etc.
Leaf spot (black spot): Alternaria panax Whetz. The pathogen is a type of fungus belonging to the Deuteromycetes. This disease mainly damages the leaves. Stems and fruits are also affected when mature. It begins to occur in mid-June, with the peak incidence from July to August. Leaf lesions are initially round or irregular and water-soaked, then gradually expand, becoming yellowish-brown with wavy concentric rings, and are easily broken. Affected stems and flower stalks develop dark brown elongated spots. When air humidity is high, especially during the rainy season, the disease spreads rapidly, and in severe cases causes early withering and death of the plants.
Control methods: Timely install shades and insert flower branches for rain protection, and maintain good sanitation on the bed surface and working paths; before or during disease occurrence, spray with a 400-fold dilution of 5% Tianan aqueous solution; 1:1:120 Bordeaux mixture; a 500-fold dilution of 65% wettable zineb; a 600- to 800-fold dilution of 50% wettable thiram; or a 600-fold dilution of 50% wettable carbendazim, etc.
Phytophthora blight: Phytophthora cactorum Leb. et Cohn. Also known as "drooping towel." The pathogen is a type of fungus belonging to the Oomycetes. It occurs during the rainy season from July to August. It mainly infects leaves, and stems and roots can also be affected. Plants aged four years and above are especially severely affected. Leaf lesions are water-soaked and dark green, and develop very quickly. Once infected, the leaves of the whole plant wilt and droop, as if scalded by hot water, hence the name. When roots are infected, they become yellowish-brown and soft-rotted, the root bark is easily peeled off, and the internal tissue shows yellowish-brown irregular patterns with a fishy odor. After onset, white mycelium often appears on the outer bark, adhering to soil particles and forming clumps. The disease is prone to occur during continuous summer rainfall and high humidity.
Control methods: Maintain good ventilation and drainage conditions in the ginseng beds, timely install shades and insert flower branches to prevent rain intrusion; increase the application of phosphorus and potassium fertilizers to improve disease resistance; immediately pull out and burn diseased plants, and disinfect the diseased holes with 5% lime milk; before disease occurrence, spray with 1:1:120 Bordeaux mixture or a 500-fold dilution of 65% zineb; use a 500-fold dilution of Dexon once every 7 to 10 days, for 2 to 3 consecutive applications.
Rusty root rot: Ramularia panacicola Zinss. The pathogen is a type of fungus belonging to the Deuteromycetes. It can occur throughout the year, with the peak incidence from June to July. Plants from the seedling stage to maturity can all be infected. It mainly attacks the roots, rhizome heads, and overwintering buds, and the diseased parts show yellowish-brown dry rot. After the roots and rhizome heads are affected, the lesions are initially yellowish-brown and gradually expand into the internal tissue. Soft, small granular substances appear in the diseased area, causing the epidermis to rupture. After scraping off the decayed material, sunken scars are revealed. There is a clear boundary between the diseased part and healthy tissue, but bacteria often invade through the wounds of the diseased part, accelerating root rot, and eventually causing the entire ginseng root or rhizome head to rot away. After the roots and rhizome heads are infected, the aboveground part initially shows no change, but later red or yellowish-brown lesions appear on the leaves, and finally the entire leaf turns red and wilts and dies. After the overwintering buds are affected, they turn yellowish-brown and often rot underground, unable to sprout and grow. The disease is severe when the soil is clayey, has high water content, and has poor aeration.
Control methods: Strictly select disease-free ginseng seedlings. The ginseng field should be thoroughly plowed, loosened, and shaded to prevent excessive soil moisture; when the disease is severe, dig up the ginseng plants in autumn, soak the roots in 1:1:100 Bordeaux mixture or a 100-fold dilution of 65% wettable zineb for 10 minutes without soaking the bud scales, and replant in disease-free land.
Sclerotinia rot: Sclerotinia sp. The pathogen is a type of fungus belonging to the Ascomycetes. This fungus occurs from May to June and also spreads after autumn. It mainly attacks the roots of ginseng aged four years and above, and bud scales and rhizome heads can also be affected. In the early stage of root infection, there is no abnormality in appearance, but the internal tissue is soft and easily crushed when pressed with a finger, then gradually becomes grayish-black and soft-rotted. White mycelium grows on the affected part. In the later stage, only the skin and fibrous tissue of the ginseng root remain, and finally black mouse-dropping-like sclerotia form inside the root bark, causing the root to rot away. The aboveground stems and leaves of diseased plants appear slightly shrunken in the early stage and wither and die in the later stage. The disease is prone to occur and spread in spring and autumn when temperatures are low, humidity is high, and soil aeration is poor.