How to prevent and control southern blight? A detailed guide to practical control techniques
Southern blight, also known as sclerotial root rot and sclerotial seedling blight, damages the root collar of seedlings and young trees. It mainly affects many tree species such as oil tea, tung tree, catalpa, citrus, apple, Chinese parasol, paulownia, walnut and masson pine, and can also cause disease in many crops such as peanut and Welsh onion. It is mainly distributed in southern and southwestern Henan Province. Let us take a look at the control techniques for southern blight below!
Symptoms of southern blight
Southern blight usually occurs at the root collar or base of the stem of seedlings. The cortex of the affected root collar gradually turns brown and necrotic, and in severe cases the cortex rots. After a seedling is affected, the absorption of water and nutrients is impaired, resulting in poor growth: the aboveground leaves become smaller and yellow, the internodes of the shoots shorten, and in severe cases the branches and leaves wither. When the lesion encircles the stem completely, the whole plant dies. Under humid conditions, the surface of the affected root collar or the soil surface near the ground is covered with white silky mycelium. Later, many small sclerotia the size of rapeseeds form within the mycelium, initially white, then gradually turning pale yellow to yellowish brown, and later tea brown. The mycelium gradually extends downward to the roots, causing root rot. The leaves of some tree species can also be affected, showing concentric-ring-shaped brown lesions on the diseased leaves, on which small sclerotia grow.
The pathogen of southern blight
The asexual generation of the pathogen causing southern blight in trees is Sclerotium rolfsii. The optimum temperature for the development of the southern blight pathogen is 30°C, the maximum is about 40°C, and the minimum is 10°C. It can grow at a pH between 1.9 and 8.4, and reproduces best at pH 5.9. Light promotes the production of sclerotia. The sclerotia germinate under suitable conditions and have no dormant period; under unfavorable conditions they can enter dormancy. The 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 land with fertile soil, loose texture and good drainage. A nursery with a severe disease history in the previous crop should be rotated with grass-family crops for more than 4 years before seedlings can be raised there 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 planting trees, 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 pits. For lightly affected seedlings, the soil at the root collar can be dug open, the root collar exposed to the sun for several days, or quicklime spread, to disinfect the soil.
4. Strengthen management: During the seedling growth period, timely fertilization, watering, drainage, and intertillage weeding should be carried out to promote vigorous seedling growth and improve disease resistance. In summer, protect against intense sun exposure to reduce scorch damage and reduce opportunities for pathogen infection.
5. Chemical control: In the early stage of the disease, use Fengqia Genbao at 600 to 800 times dilution, or irrigate the roots of diseased plants with 1% copper sulfate solution, or use 50 grams of 25% carboxin wettable powder, add 50 kg of water, and irrigate the roots of diseased plants. Alternatively, use 50 milliliters of 20% tolclofos-methyl emulsifiable concentrate per mu, add 50 kg of water, and spray once about every 10 days.