What are the symptoms of corn banded leaf and sheath blight?
Corn banded leaf and sheath blight is a disease that occurs commonly nationwide and whose damage is becoming increasingly serious. So what are the symptoms of corn banded leaf and sheath blight? Let us take a look together.
1. Main symptoms
It mainly damages the leaf sheath, and can also damage the stalk, and in severe cases causes the ear to be damaged. In the early stage of the disease, dark green water-soaked lesions mostly appear on the leaf sheaths of the 1st to 2nd stem nodes at the base, and later expand and merge into irregular or cloud-patterned large lesions. The center of the lesion is grayish brown and the edge is dark brown, spreading and expanding from bottom to top. Infection of the husk leaves of the ear also produces the same cloud-patterned lesions. After the ear is infected, the tip is bare, and the kernels are thin and flat or turn brown and rot. In severe cases, the tissue at the base of the root and stem turns grayish white, and the secondary roots turn yellowish brown or rot. When rainy conditions and high humidity last for a long time, dense white mycelium grows on the diseased parts, and the mycelium further aggregates into multiple mycelial masses, forming small sclerotia.
2. Transmission routes
The pathogen overwinters as mycelium and sclerotia in diseased residues or in the soil. The following spring, when conditions are suitable, the sclerotia germinate and produce mycelium that invades the host, after which the diseased parts produce aerial mycelium that continuously expands near the diseased tissue. When the mycelium invades the epidermal tissue of corn, it produces infection structures. Six days after inoculation, the mycelium expands longitudinally along the junctions of epidermal cells, then branches longitudinally, transversely, and diagonally; the tips of the hyphae thicken, producing lateral branches that entangle into masses, closely attaching to the surface of the host tissue to form infection cushions and appressoria. Electron microscopy observations found that appressoria directly penetrate the host epidermis with hyphae or invade through stomata, and then expand within the corn tissue. Twelve days after inoculation, hyphae are found in the cells of the lower leaf sheaths; some fill the cells, and some penetrate the cell walls into adjacent cells, causing the protoplasm to granulate, and finally the cells disintegrate; sixteen days after inoculation, AG-IIA extends hyphal clusters from the corn stomata, and water-soaked spots appear on the leaves; twenty-four days later, AG-4 shows disease symptoms on the husk leaves and lower leaf sheaths. Reinfection occurs through contact with neighboring plants, so this disease is a short-distance infectious disease.
3. Control methods
1. Remove the pathogen and plow deeply in time to eliminate diseased residues and sclerotia. In the early stage of the disease, remove diseased leaves, and apply chemicals to the diseased parts such as leaf sheaths.
2. Select disease-resistant (tolerant) varieties or hybrids, such as Yunuo No. 2 (Henuo × Hengbai 522), Benyu No. 12, etc. Practice crop rotation, plant at a reasonable density, pay attention to ditching and drainage, reduce field humidity, and eliminate field weeds in combination with intertillage.
3. Chemical control: treat seeds with Jinzhongling at 0.02% of seed weight, then pile and cover for 24 to 48 hours. In the early stage of the disease, spray 1% jinggangmycin 0.5 kg mixed with 200 kg water, or 50% thiophanate-methyl wettable powder at 500 times dilution, 50% carbendazim wettable powder at 600 times dilution, 50% benomyl wettable powder at 1500 times dilution, 50% tuijunte wettable powder at 800 to 1000 times dilution; 40% junhejing wettable powder at 1000 times dilution, or 50% nongliling or 50% speedkel wettable powder at 1000--2000 times dilution may also be used. The focus of spraying is the base of the corn plant, to protect the leaf sheath.
4. It is recommended to spray Yizhailing mixture in the early stage of the disease; for specific methods, see the Yizhailing mixture user guide.