Rice blast may occur during the entire growth period of rice, and has the characteristics of long duration of infestation, multiple sites of infection, and multiple symptoms. According to their different time and location of damage, they can be divided into seedlings, leafhoppers, knots, leaf pillows, panicles, and grains. The incidence of leaf aphid and panicle blast is the highest and the damage is the heaviest.
1. Miao Miao: Occurred in the seedlings before the three-leaf stage. The common seedbeds in our area are not common. However, susceptible varieties may occur when the temperature is high and the humidity is high.
2. Leafhoppers: Occurrence of seedlings or adult plant leaves after the three-leaf stage. The period from the tillering stage to the jointing stage is the peak period. The lesions on the leaves are often caused by differences in the disease resistance of the climate and varieties. The lesions are in shape, Different sizes and colors can be divided into four types: chronic type, acute type, white point type, and brown point type. Chronic type and acute type are the most serious ones.
(1) Chronic type: The lesions are fusiform or spindle-shaped, generally 1 to 1.5 inches long, 0.3 to 0.5 inches wide, the lesions are gray in the center, the edges are brown, and the periphery often has pale yellow halos. A brown necrotic line extending towards the veins with a gray moldy layer on the back. The lesions are interconnected for a long time to form irregular large spots, and the leaves die when they are severe.
(2) Acute type: lesions are nearly round or oval with dark green water stains, and lesions are closely stained with gray mold layer. The appearance of acute lesions is a sign of a field popping pandemic.
(3) White point type: The lesions are mostly on the young leaves of rice, and they are nearly round white dots, and the conditions can be properly changed to acute lesions.
(4) Brown spots: Spots on the old leaves of rice produce only needle-sized brown spots, confined between the two leaf veins.
3. Frugality: It began to occur from late July to early August. It mostly occurred on the first and second sections under the flag leaf of rice after heading. It initially produced brown dots on the stem sections and gradually expanded around the section. In the end, the entire section becomes brown or black, resulting in bending or breaking of the stalk section, and the diseased part has a gray moldy layer when it is wet, which affects rice sturdiness or the formation of white spikes.
4, leaf pillow: occurs at the junction of leaves and leaf sheaths, lesions were gray-green, its appearance indicates the occurrence of panicle blast.
5. Ear and neck ridges: The symptoms appear at about 10 days after ear emergence. Rice is most susceptible to heading at the heading stage. It occurs on the neck, rachis, and branches. The diseased section becomes brown and necrotic, and the spikes and spikes are easily broken. White spike, commonly known as "æŽ neck 瘟".
6. Grain pods: Occur in the rice chaff and chert. The early lesions were oval in shape and gray in the middle. Afterwards, the whole grain turned into dark gray granules; late onset often formed irregular dark brown spots.
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