Symptoms of the disease include wheat leaf blight, which commonly occurs during the heading stage of wheat. It primarily affects the leaves and leaf sheaths. Initially, small yellow or pale green spots appear on the lower leaves, which quickly expand into irregular yellow to white patches. In severe cases, large brown lesions may develop and spread upward from the lower leaves. During late autumn and early spring, the bacteria can invade the root canopy, leading to the death of lower leaves, weakening the plant, and even causing its death. Lesions on the stems and ears are usually less noticeable and smaller compared to those on the leaves. Conidia production is also limited.
Morphological characteristics: The conidia are spherical to oval in shape, with a brown to black wall and a slightly raised pore. They are often found within the stomata beneath the host’s epidermal tissue. Two types of conidia are produced—large spores that are slender and colorless, containing 3–7 septa and circular ends, while microspores lack septa, are curved, and remain colorless.
Disease characteristics: In winter wheat regions, pathogens survive on wheat residue or seeds during summer and begin infecting seedlings in the fall. Most of the bacterial population dies off during winter. In the following spring, the pathogen produces conidia for transmission. In spring wheat areas, conidia and mycelium overwinter on crop residues and become active after planting in the next spring. This disease thrives under low temperature and high humidity conditions. There is significant variation in resistance among different wheat varieties against leaf blight.
Control methods:
1. Use disease-free seeds and plant them at an appropriate density. Apply sufficient base fertilizer and manage NPK levels to control plant population density, improving air circulation and light penetration in the field.
2. Seed treatment: Dress seeds with 0.2%–0.3% of 50% thiram wettable powder or 33% mancozeb WP at a rate of 0.2% of the seed weight.
3. The critical period for controlling leaf blight is from the filling to flowering stage of wheat. Apply 12.5% diniconazole WP at 25–30 grams per 50 kg of water, or 20% triadimefon EC at 100 ml per 50 kg of water. Alternatively, use 50% carbendazim WP diluted 1000 times, 50% thiophanate-methyl WP diluted 1000 times, 75% chlorothalonil WP diluted 500–600 times, or 50% iprodione WP diluted 1500 times. Spray once or twice depending on the field condition.
Source: Xihua County Agricultural Bureau, Henan Province
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