How to prevent and control peanut southern blight? First, recognize the damage symptoms

Peanut southern blight is one of the main diseases harming peanuts. After the roots, pods and stem base of the peanut are affected, they initially become brown and soft-rotted. White silky mycelium appears at the root-stem area of the aboveground part. White silky threads often first form at the stem base near the ground and on the nearby soil surface, and the diseased part gradually turns dark brown and glossy. Now let us take a look at the prevention and control methods for peanut southern blight.

Damage symptoms of peanut southern blight

Under high-humidity conditions, the aboveground part of infected plants can be covered by white mycelial strands, which then spread to the nearby soil surface and infect other plants. In extremely humid environments, the mycelial clusters are not obvious, while the affected stem base is covered by long spindle-shaped lesions with light brown to red suberized raised areas. Under drought conditions, lesions on the stem occur below the soil surface, are brown and spindle-shaped, about 0.5 cm long, and bear rapeseed-like sclerotia. The stems and leaves turn yellow and gradually die, and the peanut pods rot.

Conditions for the outbreak of peanut southern blight

The pathogen overwinters as sclerotia or mycelium in the soil or on diseased residues and can survive for 5-6 years. Most are distributed in the 1-2 cm surface soil layer. For sclerotia below 2.5 cm, the germination rate decreases markedly, and at 7 cm in the soil they almost do not germinate. The next year, the sclerotia germinate and produce mycelium, which invades through the epidermis or wounds at the base of the plant's root-stem area, and can also invade the gynophore or pods. Seeds can also carry the pathogen. In the field, the pathogen spreads through flowing water or insects. High temperature, high humidity, heavy clay soil, poor drainage, low-lying land and rainy years make the disease more likely to occur. If it turns clear right after rain, diseased plants wilt and die rapidly. Continuous cropping and early sowing result in more severe disease.

Prevention and control methods for peanut southern blight

1. After harvest, promptly remove diseased residues and deep-plow, and rotate for more than 3 years with gramineous crops such as rice, wheat and corn. Encourage the application of compost fermented with effective microorganisms or decomposed organic fertilizer to improve soil aeration.

2. Sow spring peanuts appropriately later, and clear the seedlings and promote root development during the seedling stage to improve disease resistance. At the same time, select disease-free seeds and treat them with 50% carbendazim wettable powder at 0.5% of seed weight. After disease onset, use 1 kg of 50% seed-dressing dual powder mixed with 15 kg of fine dry soil to make medicated soil to cover the diseased holes, using 75 g of medicated soil per hole.

3. At the early stage of disease, spray or drench with Fengqia Genbao at 600-800 times dilution, or 50% benomyl wettable powder, or 50% iprodione wettable powder, or 50% procymidone (Sumilex) wettable powder, or 20% tolclofos-methyl emulsifiable concentrate at 1000-1500 times dilution, applying 100-200 ml of the prepared solution per plant.

Damage symptoms and prevention and control methods of plant southern blight (pictures)

Southern blight is also called sclerotial root rot and sclerotial seedling blight. It harms the root-stem area of seedlings and young trees, mainly affecting 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. Now let us take a look at the prevention and control techniques for southern blight.

Symptoms of southern blight

Southern blight usually occurs at the root-stem area or stem base of seedlings. The cortex of the affected root-stem area 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 shoots shorten. In severe cases, branches and leaves wilt, and when the lesion encircles the stem, the whole plant dies. Under humid conditions, the surface of the affected root-stem area or the nearby soil surface is covered with white silky mycelium. Later, many rapeseed-like small sclerotia form within the mycelium, initially white, then gradually becoming light yellow to yellow-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, with concentric-ring brown lesions appearing on diseased leaves, and small sclerotia growing on the lesions.

Pathogen of southern blight

The asexual generation of the pathogen causing tree southern blight is Sclerotium rolfsii. The optimum 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 1.9-8.4, and reproduces best at pH 5.9. Light can promote sclerotium production. Sclerotia germinate under suitable conditions and have no dormant period; they can enter dormancy under unfavorable conditions. Sclerotia can survive in soil for 5-6 years, and survive even longer under low-temperature and dry conditions.

Prevention and control of southern blight

1. Nursery site selection: The seedling-raising land should be chosen as fertile soil, loose in texture and well-drained. A nursery 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 land, 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 g of 70% quintozene wettable powder per mu, add 20 kg of fine soil, mix well and scatter it in the sowing furrow or around the tree holes. For lightly affected seedlings, the soil around the root-stem area can be dug open, the root-stem area sun-dried for several days, or quicklime scattered to disinfect the soil.

4. Strengthen management: During the seedling growth period, timely fertilize, water, drain and cultivate to control weeds, promote vigorous seedling growth and improve seedling disease resistance. In summer, prevent sunscald to reduce burn damage and reduce opportunities for pathogen infection.

5. Chemical control: At 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 g of 25% carboxin wettable powder added to 50 kg of water to irrigate the roots of diseased plants. Alternatively, use 50 ml of 20% tolclofos-methyl emulsifiable concentrate per mu, added to 50 kg of water, and spray once every 10 days or so.

How to prevent and control peanut southern blight with good results

Peanut southern blight causes relatively great harm to peanut plants and pods. In severe cases, it can even cause plants to wither and die, which inevitably gives farmers headaches. So how can it be controlled effectively? Let us take a look.

Prevention and control methods for peanut southern blight

(1) Deep plowing to improve the soil and strengthen field management. Before peanut harvest, remove diseased residues. After harvest, deep-plow the soil to reduce overwintering sources of the pathogen in the field. After peanut sowing, ensure the "three ditches" are complete, and promptly drain accumulated water from the field after rain.

(2) Chemical control. At the early pod-setting stage of peanut, spray 20% triadimefon emulsifiable concentrate at 1000 times dilution, or iprodione at 1000 times dilution, for control. During the disease period, root irrigation with agents such as triadimefon, Genfuling and thiophanate can also be used, and the control effect is very obvious.