Identification and Control Methods of Southern Blight in Japanese Euonymus

Southern blight in Japanese euonymus is caused by a fungus and is characterized by being highly destructive and spreading rapidly. If not controlled properly, it can cause the death of all seedlings. Based on past work, we have summarized the characteristics and control methods of southern blight in Japanese euonymus.

Symptoms: In the early stage of the disease, the stem or leaf base near the soil turns brown and rots. After a few days of sun exposure, white silky mycelium appears on the diseased parts and soil surface, spreading radially through the rhizosphere soil. Later, brown, rapeseed-shaped small sclerotia grow on the stem near the soil surface, often causing the death of the entire plant. The leaves first appear darkened and lose their green color, eventually turning yellow and withering.

Disease pattern: The pathogen overwinters in the soil in the form of sclerotia (sclerotia have strong resistance to adverse conditions and can survive in soil for 5 to 6 years). In the second year, when conditions are suitable, the sclerotia germinate and grow mycelium, which spreads through the soil and infects the plant from the base, causing disease.

Disease conditions: Acidic soil is conducive to disease development (suitable pH range: 1.9-8.4, optimal pH value 5.9); high temperature and high humidity environments favor disease development (severe in August and September), with an optimal growth temperature of 30 to 35°C; continuous cropping soil has severe disease (soil contains more pathogens and they survive longer); clayey soil has severe disease; low-lying terrain, over-dense planting, and poor ventilation and light transmission lead to severe disease (the pathogen prefers moist, stagnant-air conditions).

Control measures:

① Strictly implement seedling entry and exit regulations, do not purchase seedlings from disease-affected areas, and prevent human-mediated spread of the disease.

② This disease is a soil-borne disease, so soil sterilization and disinfection is a key measure. You can use 0.2% quintozene or thiram mixed evenly with soil before planting, or apply 5 to 10 grams per square meter with an appropriate amount of fine soil and spread it into the soil. When planting, try to choose disease-free plots and avoid continuous cropping.

③ The plot should be basically level. Begin controlling watering in May to keep the soil surface relatively dry, and increase the application of phosphorus and potassium fertilizers. Pay attention to drainage during the rainy season. If it suddenly clears up after rain, drain the accumulated water in stages; do not drain it all at once.

④ Spray 1:1:100 Bordeaux mixture for protective prevention. In the early stage of the disease, you can use 50% carbendazim or 75% chlorothalonil 500 times dilution for spraying combined with root drenching, or use 25% propiconazole emulsifiable concentrate 2500 times dilution for spraying. This has a special effect on this disease, with a validity period of 2-5 weeks, high-efficiency systemic action, takes effect in 2 hours, and is resistant to rain washing.

⑤ After rain, promptly carry out intertillage and loosening of the soil, and do a good job in controlling other pests and diseases.

⑥ The plant and row spacing should not be too dense; promptly prune overly dense branches. Remove diseased leaves and diseased plants in a timely manner, remove mycelium and sclerotia from the soil surface and burn them in a centralized manner, and promptly disinfect the soil with fungicides.

⑦ In the north, do a good job of winter cold protection for diseased and weak seedlings.