Detailed Explanation of the Key Technical Points for the Prevention and Control of Panax notoginseng Diseases and Pests
Disease Control
(1) Panax notoginseng Root Rot
Symptoms: The field symptoms of this disease often present in two forms: (1) In the early stage, the above-ground leaves show abnormal color, the leaves wilt, turn yellow and fall off, and the underground parts rot; (2) The underground root system is affected locally, the leaves droop to one side and wilt. If the plant is pulled out in time, it can still be processed and used; otherwise, the entire root tuber rots. Disease pattern: Infection occurs through seedlings, diseased root residues, and soil-borne bacteria. The disease can occur throughout the year, with two peak periods in March—April and August—October. Because this disease is soil-borne, the pathogenic factors are complex. Four types of pathogens have been identified so far, including bacteria and fungi. Among the four pathogens, bacteria have the strongest pathogenicity, and infection can occur from the emergence of seedlings in early spring until withering.
Inadequate land preparation, heavy clay soil, poor drainage, damage to seedlings, and a history of the disease can all lead to the occurrence of root rot.
The occurrence and development of Panax notoginseng root rot depend to a large extent on environmental conditions. When the temperature is 15—20°C and the relative humidity is greater than 95%, root rot will break out or become epidemic. If the light transmittance of the shade shed is too high, the disease will be severe. Continuous cropping land has more severe disease than rotation land and newly planted land, and the longer the continuous cropping period, the more severe the disease. Fertilizer type, fertilization methods, and field management measures all directly affect the occurrence and spread of the disease, so a single chemical control measure is often difficult to effective in production. At present, the most ideal approach is to adopt comprehensive management measures combining agricultural control and chemical control.
Control measures:
1. Select suitable plots. The most suitable soil for planting Panax notoginseng is sandy loam with a pH of 6—7 (neutral to slightly acidic soil). The plot should have a certain slope to facilitate drainage during the rainy season; do not choose plots where Panax notoginseng has been planted within 5 years.
2. Select healthy seedlings for transplanting. Seedlings carrying bacteria or stored too long after digging are a major cause of root rot. Therefore, selecting healthy seedlings and transplanting them at the right time is very important. When selecting healthy seedlings, also check whether there are rotten diseased plants among the seedlings and whether diseased plant residues exist in the seedling field. If so, remove them in time, and treat the seedlings with 1:300 diluted Ridomil MZ plus Thiophanate-methyl or Carbendazim for 30 minutes, then transplant with the pesticide.
3. Apply decomposed fertilizer and irrigate at the right time. Applying inadequately decomposed farmyard manure is one of the causes of root and bud rot. Therefore, if using farmyard manure such as pig manure or oil cake, it must be composted for more than 3 months to make it fully decomposed, and nitrogen chemical fertilizers should be applied sparingly.
4. Strengthen winter management. Remove diseased residues in time and carry out disinfection treatment, which can be done with Carbendazim or Ridomil MZ at 1:500 dilution.
5. Chemical control. This is an auxiliary measure for preventing and controlling Panax notoginseng root rot. Bactericidal agents such as Yekujing and Yekuning and fungicidal agents such as Dexon and Carbendazim can be used in combination. According to experiments: applying 1 kg each of 10% Yekujing (Yekuning) plus 70% Dexon per mu made into medicinal soil and broadcast applied achieved a control effect of more than 70%.
(2) Panax notoginseng Black Spot Disease
Symptoms: In the early stage, the affected part shows elliptical light brown lesions, which then turn dark brown. The lesions expand upward and downward, become sunken, and produce black mold-like substances, finally causing twisting and breaking followed by death.
Disease pattern: Diseased seeds and bacteria-carrying seedlings are the main routes of transmission of black spot disease. When the temperature is 18°C and the relative humidity is 80%, it can germinate and infect plants. High temperature and high humidity cause severe disease, and continuous rainfall or typhoon rainstorms will intensify the epidemic. The light transmittance of the shade shed, fertilization, and other cultivation measures directly affect the occurrence and development of the disease.
Control measures:
1. Select and retain disease-free seeds. When collecting seeds, select seeds from disease-free fruits and eliminate diseased fruits and seeds.
2. Seed and seedling treatment. Seeds and seedlings are sources of pathogens, so seed disinfection must be carried out when sowing. Soak seeds in 58% Ridomil MZ or 64% Sandofan at 1:500 dilution for 20—30 minutes.
3. Eliminate and block infection centers. Check frequently, and when central diseased plants are found, immediately remove them and carry out chemical protection around them. Only in this way can the development of the disease be effectively controlled.
4. Strengthen cultivation management. Reasonably dense planting and ensure uniform light transmission in the Panax notoginseng garden. Excessive light transmission easily induces disease occurrence, so it is best to use shade nets for cultivation.
5. Maintain field sanitation. After the plants are set, promptly remove dead branches, fallen leaves, and mulch from the Panax notoginseng garden, and spray pesticides for prevention.
6. Chemical control. During the seedling emergence and leaf unfolding stage of Panax notoginseng, finding black spot diseased plants indicates an infection center. Treating the central diseased plants is the best time to start spraying. The number of sprays and interval time should be determined according to forecasts and climatic conditions. Generally, spray once every 7—10 days. There are many pesticides used to control black spot disease. In the early stage of the disease, use the following pesticides alternately or mix two of them (except Polyoxin): 64% Sandofan wettable powder at 1:300—500 dilution, 64% Ridomil MZ wettable powder at 1:300—500 dilution, 40% Dimethachlon wettable powder at 1:400 dilution, 1.5% Polyoxin wettable powder at 1:500 dilution, 40% Daconil wettable powder at 1:500 dilution.
Appendix: Routine inspection method for Panax notoginseng black spot disease
1. Inspection instrument: Microscope
2. Inspection reagents: 95% alcohol, glacial acetic acid, saturated chloral hydrate
3. Inspection method: Randomly cut 4—5 Panax notoginseng leaves in the field, place them in a mixed solution of equal amounts of 95% alcohol and glacial acetic acid, fix for 24 hours, then immerse them in saturated chloral hydrate solution. After the tissue becomes transparent, the conidia of black spot disease can be observed, thereby predicting the occurrence trend of black spot disease and guiding field pesticide application.
(3) Panax notoginseng Damping-off and Seedling Blight
Both are major diseases in the seedling stage of Panax notoginseng, and their symptoms are similar and difficult to distinguish.
Damping-off generally occurs at the base of the seedling stem, that is, at the boundary between dry and wet soil 3—5 cm from the surface soil layer. After the pathogen invades, the tissue at the affected site softens. In the early stage, the stem base shows yellow-brown sunken elongated lesions, which gradually penetrate into the stem and rot, causing the seedling to lodge and die.
Seedling blight generally occurs near the ground surface in the early stage of disease. The affected part shows water-soaked dark lesions, and the stem shrinks, softens, lodges, and dies; when humidity is high, a layer of gray-white mold often appears on the surface of the affected part. Both damping-off and seedling blight occur on the stems of Panax notoginseng seedlings, but damping-off occurs at the boundary between dry and wet soil 3—5 cm from the surface soil, while seedling blight occurs near the ground surface on the above-ground stem. This is one of the main characteristics for distinguishing the two different diseases.