Illustrated Guide to Symptoms and Control Methods of Southern Blight in Plants

Southern blight, also known as sclerotial root rot and sclerotial seedling blight, affects the root crown of seedlings and young trees. It mainly damages many tree species such as oil tea (Camellia oleifera), tung tree (Vernicia fordii), catalpa (Catalpa), citrus, apple, Chinese parasol (Firmiana simplex), paulownia, walnut, and Masson pine (Pinus massoniana), and can also cause disease in many crops such as peanut and scallion. It is mainly distributed in southern and southwestern Henan Province. Let's take a look at the control techniques for southern blight below!

Symptoms of Southern Blight

Southern blight usually occurs at the root crown or stem base of seedlings. The cortex of the infected root crown gradually turns brown and necrotic, and in severe cases the cortex rots. After seedlings are affected, the absorption of water and nutrients is impaired, resulting in poor growth. The aboveground leaves become smaller and yellow, and the internodes of branches and shoots shorten. In severe cases, the branches and leaves wilt, and when the lesion encircles the stem completely, the entire plant dies. Under humid conditions, the surface of the affected root crown or the soil surface near the ground is covered with white silky mycelium. In the later stage, many small sclerotia resembling rapeseeds form within the mycelium, initially white, gradually turning pale yellow to yellowish brown, and later turning tea-brown. The mycelium gradually extends downward to the roots, causing root rot. Some tree species can also be affected on their leaves, with concentric-ring-patterned brown lesions appearing on diseased leaves, and small sclerotia growing on the lesions.

Pathogen of Southern Blight

The asexual generation of the pathogen causing southern blight in trees is Sclerotium rolfsii. The optimal temperature for the development of the southern blight pathogen is 30°C, with a maximum of about 40°C and a minimum of 10°C. It can grow at pH values between 1.9 and 8.4, with pH 5.9 being most suitable for reproduction. Light can promote the production of sclerotia. Sclerotia germinate under suitable conditions and have no dormant period; they can become dormant under adverse conditions. Sclerotia can survive in soil for 5 to 6 years, and survive even longer under low-temperature and dry conditions.

Control of Southern Blight

1. Nursery site selection: The seedling-raising site should be chosen as land with fertile soil, loose texture, and good drainage. Nurseries with severe disease in the previous crop should be rotated with gramineous crops for more than 4 years before seedlings can be raised again.

2. Deep plowing in winter: In affected nursery sites, deep plowing should be carried out every winter to bury diseased plant residues deep in the soil and eliminate sources of infection.

3. Soil disinfection: Before raising seedlings or afforestation, use 1000 grams of 70% quintozene wettable powder per mu, add 20 kg of fine soil, mix well and spread it in the sowing furrows or around the tree holes. For lightly affected seedlings, the soil around the root crown can be dug open, the root crown exposed to the sun for several days, or quicklime can be spread for soil disinfection.

4. Strengthen management: During the seedling growth period, timely fertilization, watering, drainage, and cultivation with weeding should be carried out to promote vigorous seedling growth and improve disease resistance. In summer, protection against intense sunlight is needed to reduce sunscald damage and decrease opportunities for pathogen infection.

5. Chemical control: In the early stage of disease, use Fengqia Genbao at 600-800 times dilution, or irrigate the roots of diseased plants with 1% copper sulfate solution, or use 50 grams of 25% carboxin wettable powder mixed with 50 kg of water to irrigate the roots of diseased plants. Alternatively, use 50 mL of 20% tolclofos-methyl emulsifiable concentrate per mu mixed with 50 kg of water, spraying once every 10 days or so.

Symptoms and Control Methods of Southern Blight in Climbing Fig (Ficus pumila)

[Symptoms] The disease occurs at the base of the plant. Initially, the area where the leaf base meets the soil becomes water-soaked; soon it turns brown, rots, and produces a white silky mycelial layer that mostly spreads radially toward the soil surface near the roots; ultimately the entire leaf cluster dies. Within the white mycelial layer of the diseased area, sclerotia the size of oil seeds are also produced, initially yellowish-white and later turning yellowish-brown.

[Pathogen] Southern blight is caused by infection from a fungus called Sclerotium rolfsii. The pathogen survives in soil as sclerotia and has strong resistance to adverse environments, able to survive in soil for 3-5 years. However, under waterlogged conditions, it can only survive for 3-4 months.

[Occurrence pattern] High temperature and high humidity conditions are favorable for disease occurrence, so the disease is severe in the hot and rainy months of August to September; acidic sandy soil, as well as pathogen-contaminated potting soil or continuous cropping land, is prone to the disease, and the damage is also severe.

[Control methods] 1. Eliminate infection sources: Promptly remove diseased leaves and diseased plants and burn them centrally to prevent sclerotia from entering the soil. After removing diseased plants, the diseased holes can be disinfected by spreading lime or other medicated soil.

2. Strengthen cultivation management: Planting or flower pot placement should not be too dense, and good ventilation conditions should be maintained. In severely affected planting areas, rotation with gramineous plants for more than 4 years should be carried out to reduce the damage of this disease.

3. Chemical control: Fungicides such as quintozene, dexon, thiram, or carbendazim can be used at 5-10 grams per square meter, mixed with an appropriate amount of fine soil, and evenly spread into the soil or

Symptoms and Control Methods of Southern Blight in Peony (Paeonia)

The scientific name of southern blight in peony is Sclerotium rolfsii. The disease mainly damages the stem base of medicinal plants, affecting their normal growth. Growers should promptly understand the symptoms and control methods of southern blight in peony.

Symptoms of southern blight in peony:

The affected parts are the stem base and roots. In the early stage, the stem base becomes water-soaked, reddish-brown, and irregular in shape. In severe cases, the stem base and roots turn brown and rot, growing a white silky mold layer and simultaneously producing nearly spherical reddish-brown sclerotia. The aboveground parts turn yellow and wilt. Leaf lesions are nearly circular, brown, slightly concentric-ringed, and water-soaked.

Occurrence environment and conditions of southern blight in peony:

It overwinters in the soil as sclerotia or mycelium with diseased residues. Mycelium can also spread directly through soil cracks on the surface, and sclerotia are transferred by flowing water. Acidic soil, poor drainage, heavy clay soil, and poor plant growth are conducive to the disease, and high temperature and high humidity favor its occurrence.

Control methods for southern blight in peony:

(1) Plant at a reasonable density to create conditions for ventilation and light penetration.

(2) Before planting, soak the rhizomes and reed heads in 800 times dilution of 50% carbendazim wettable powder for 5 minutes.

(3) Upon finding diseased plants, immediately pull them out and burn them, and spread quicklime in and around the diseased holes for disinfection, or use 1000 times dilution of 70% thiophanate-methyl wettable powder to drench the diseased holes and the root crown area of surrounding plants.