Occurrence and Control Methods of Common Diseases in the Middle and Late Growth Stages of Salvia miltiorrhiza
I. Phytophthora Blight
1. Symptoms and Causes
In the early stage of the disease, the lower leaves of the aboveground plant turn yellow, and the top leaves lose water and wilt at noon during high temperatures, but can still recover in the morning and evening; in the later stage, the entire plant's leaves wilt and no longer recover, and rotting begins from the base. When the underground root and rhizome of Salvia miltiorrhiza are pulled out, the main root epidermis appears water-soaked and turns pale yellow; peeling back the epidermis reveals that the pith is completely rotted, with the rotted pith retaining its color, having a slight odor, and appearing as a wet rot. This disease spreads rapidly, and generally infected plants die within 1—2 weeks. When soil moisture is high, it can occur shortly after transplanting Salvia miltiorrhiza seedlings and spread quickly, with white mold-like substances intermittently produced on the roots, which are the mycelium or fruiting bodies of the pathogen. The pathogen is Phytophthora cactorum (Leb.et cohn) Schroet., commonly known as Phytophthora cactorum, a fungus belonging to the subphylum Mastigomycotina. It spreads through irrigation water and rainwater to the sprouting buds of Salvia miltiorrhiza, and under high temperature and high humidity conditions, lesions appear within 2—3 days, spreading through wind and rain. The severity of this disease is directly related to the timing of the rainy season, temperature levels, and rainfall amounts in that year. If the temperature is high in early spring, there is abundant rain, and frequent flood irrigation is used, the disease incidence is severe and spreads widely.
2. Control Methods
(1) Implement crop rotation of more than 3 years. Plots with a history of the disease must strictly avoid continuous cropping.
(2) After selecting the soil, carry out winter plowing and sun-drying of the soil clods in winter. It is best to apply compost fermented with effective microorganisms, increase the application of phosphorus and potassium fertilizers, and control nitrogen fertilizer.
(3) Adopt raised bed cultivation and use plastic film mulching, which can effectively reduce the chance of pathogen infection.
(4) After heavy rain or irrigation, promptly spray pesticides for prevention, or broadcast quicklime for disinfection.
(5) After discovering diseased plants, use pesticides for treatment and to prevent spread.
A. Spray with 72% cymoxanil mancozeb (Kekangling) wettable powder at 800 times dilution.
B. Spray with 72% DuPont Curzate or 72% Keshuangqing wettable powder at 1000 times dilution.
C. 18% metalaxyl mancozeb wettable powder at 600 times dilution.
D. 70% ethylicin mancozeb wettable powder at 500 times dilution.
Any one of the above pesticides, mixed well as required, use 50 kg of the prepared solution per mu, spray once every 7 days, alternating sprays for 3 times. Note that spraying must be uniform, ensuring no repeated spraying and no missed spraying.
II. Sclerotinia Rot
1. Disease Symptoms
The stem base, root buds, and rhizome area of diseased plants gradually rot, turning dark brown, and the plants wilt and die. On the diseased parts, inside the stem base, and on the nearby soil, there are sclerotia that are black, mouse-dropping-shaped, and accompanied by white mycelium.
2. Control Methods
(1) Maintain soil moisture content, control excessive soil moisture, and promptly carry out soil cultivation and loosening.
(2) During the disease period, mix 0.5 kg of 50% chlornitrofen with 10 kg of quicklime to make a sterilizing agent, and broadcast it on the base of diseased plants and the nearby soil.
(3) Drench the base of diseased plants and the nearby soil with 50% Sumilex at 1000 times dilution.
III. Salvia miltiorrhiza Root Rot
1. Disease Symptoms
In the early stage of the disease, individual lateral roots or fibrous roots turn brown and begin to rot, then gradually spread to the main root, the outer skin turns black, and the entire root rots. Individual stems and branches of the aboveground plant die first, and finally the entire plant dies. This disease mostly occurs from May to November.
2. Control Methods
(1) Pay attention to selecting propagation materials for planting. In recent years, artificial cultivation of Salvia miltiorrhiza mainly adopts a combination of sexual reproduction and asexual cultivation (i.e., raising seedlings from seeds and transplanting), which effectively solves the problem of disease carried by traditional pure asexual propagation old seed roots, and is the foundation for controlling Salvia miltiorrhiza root rot.
(2) Disinfect seedlings before cultivation. Soak seeds with 50% thiophanate-methyl for 6 hours or with 5% plant ash solution for 2 hours.
(3) Strictly select soil and terrain. Choose plots with high terrain and good drainage for planting. The soil must be medium loam or loam, ensuring good water permeability and aeration; the terrain should preferably have a slope of 10-15 degrees. If the terrain is flat, deeper and densely distributed drainage ditches must be dug.
(4) During continuous rainy weather and when the soil is relatively moist, as long as field cultivation is possible, carry out various forms of cultivation and soil loosening multiple times to break the compacted soil layer, allow harmful gases in the soil to escape, let fresh oxygen from the air enter, and increase gas exchange between the soil and air. This measure can effectively prevent and reduce the occurrence of Salvia miltiorrhiza root rot. Also promptly spray fungicides for prevention.
(5) In the early stage of the disease, drench diseased plants and the surrounding area with 50% thiophanate at 800—1000 times dilution.
IV. Leaf Spot Disease
1. Disease Symptoms
Leaf spot disease is a bacterial disease that mainly harms leaves. On the upper surface of Salvia miltiorrhiza leaves, nearly circular or irregular dark brown lesions appear. In severe cases, the lesions expand and merge, causing the leaves to wither and die. It begins to occur in May and continues until late autumn, with severe incidence in June—July.
2. Control Methods
(1) Strengthen management and implement crop rotation.
(2) Increase the application of phosphorus and potassium fertilizers, or spray 0.3% potassium dihydrogen phosphate foliar fertilizer to improve the disease resistance of plants.
(3) In the early stage of the disease, spray 50% carbendazim at 500—1000 times dilution or thiophanate-methyl at 800 times dilution, once every 7 days, for 3 consecutive sprays.
V. Root-Knot Nematode Disease
1. Disease Symptoms
Root-knot nematode disease is a parasitic disease. Many tumor-like growths form on the roots, causing plants to be stunted, develop slowly, and leaves to lose green color and gradually turn yellow, eventually the entire plant withers and dies. When diseased plants are pulled up, there are many gall-like tumors on the fibrous roots. When picked open with a needle, small white dots can be seen with the naked eye; these small dots are female nematodes. Generally, when cultivating Salvia miltiorrhiza on soil with high sand content and good aeration, the disease is likely to occur.
2. Control Methods
(1) Avoid continuous cropping as much as possible; rotate with gramineous crops as the preceding crop.
(2) During land preparation, apply 5 kg of 3% isofenphos-methyl per mu and mix it into the soil.
(3) Mix 2—3 kg of 80% dibromochloropropane with 100 liters of water, open furrows and apply it into the soil 15 days before planting, then cover with soil to prevent the liquid from volatilizing and improve the control effect.