Identification and Control Methods of Common Rice Diseases
1. Rice blast
(1) Damage characteristics: Rice blast, also known as rice fever disease, commonly called fire blast, dangling-head blast, neck-pinching blast, etc., is one of the most widespread and most damaging fungal diseases worldwide, mainly harming the aboveground parts of the host plant. Because the damage period and site differ, it can be divided into seedling blast, leaf blast, neck blast, branch blast, grain blast, etc. Its host range includes rice, @#@245@#@, crabgrass and many other grass family plants. The rice blast pathogen mainly overwinters on diseased rice straw, and in the second year spreads from the diseased straw into rice fields to infect and cause damage. Pathogen transmission mainly relies on wind, and rain, water flow and insects can also transmit it. When the weather turns warm and there is rain, the overwintering pathogen will revive and multiply in large numbers, transferring from the diseased rice straw piled at the field edge to rice plants to cause damage.
(2) Control methods: ① Select good varieties, plant disease-resistant varieties, and use multiple combinations in a reasonable mix. ② Disinfect and sterilize seeds; soak 1 kg of seeds in 3 grams of 20% tricyclazole for 24 hours. ③ Strengthen cultivation management. ④ Soak seedlings in medicinal solution; soak seedlings in a 750-fold dilution of 20% tricyclazole wettable powder, or use 40% isoprothiolane emulsifiable concentrate at 100 ml per mu, or 100 ml of Fuji-One emulsifiable concentrate mixed with 60 kg of water for spraying. For prevention of neck blast, at the booting and breaking stage use 75% Fengdeng wettable powder at 25-30 grams per mu or 20% tricyclazole at 100 grams; for treatment of leaf blast, use rice blast-type pesticides for control.
2. Bacterial leaf blight
(1) Damage characteristics: Rice bacterial leaf blight is also called fire seedling. Bacterial leaf blight is a disease that spreads very quickly. At present, many rice-growing areas do not yet have this disease, so it is designated as a domestic plant quarantine object.
After a rice plant is infected with bacterial leaf blight, green or dark green spots appear at the leaf tip or leaf margin, and the lesions expand along the midrib or leaf margin, forming clearly defined lesions. After the lesions cause the leaf to wither and die, they appear grayish white, hence the name bacterial leaf blight. Generally, the lower and middle leaves of rice become diseased first, then it spreads to the upper leaves. This disease occurs from the seedling stage, develops commonly at the tillering stage, and reaches a peak at the booting stage, especially after heading. If the disease occurs early, the leaves wither and die, and heading cannot occur; if the disease occurs later, it affects flowering and grain filling, increases empty grains, and the stalks of diseased plants become weak and prone to lodging.
Bacterial leaf blight is easily confused with other diseases and difficult to identify clearly. You can cut a small segment from a diseased leaf, place it on a glass slide with water, then press another small piece of glass on top. After about 1 minute, place it in a slightly dim place. If a cloudy or milky white liquid flows out from the cut, this is the bacterial leaf blight pathogen.
(2) Control methods: ① Strict quarantine and use disease-free rice seed. For seed disinfection, filtered 1% limewater can be used for soaking seeds; at a temperature of 25°C, seeds can be soaked for 3-4 days. The soaked rice seed should always be kept 10-12 cm below the water surface, and the water surface must not be stirred, so as not to break the limewater film and reduce the disinfection effect. ② Select varieties resistant to bacterial leaf blight. ③ Tillering fertilizer and ear fertilizer should not be excessive. Irrigate frequently with shallow water, drain the field in a timely manner, promote robust rice growth, and improve disease resistance.
3. Sheath blight
(1) Damage characteristics: Sheath blight is also called cloud-pattern disease, with common names such as eyebrow-eye spot, flower-foot blast and moldy green stem, and is one of the important diseases of rice.
The disease begins to occur from the tillering stage, and becomes more severe the later it gets. It mainly damages the leaf sheaths and leaves near the water surface, and in severe cases also damages the upper leaf sheaths and leaves. The lesions are initially oval, with the center of the leaf grayish green, and then continuously expand into streaky irregular lesions. After the lesions expand, the leaf sheaths and leaves wither and die, tillers die, and in severe cases the rice plants cannot head or can head but cannot set grain, or early lodging is caused; mild occurrence increases empty and shriveled grains and reduces grain weight.
(2) Control methods: ① Strengthen cultivation management. Irrigate frequently with shallow water, drain the field in a timely manner, and fertilize according to the seedlings' condition, so as to promote robust rice growth and improve disease resistance, while also reducing rice field humidity, improving ventilation and light penetration, inhibiting pathogen growth and transmission, thereby effectively controlling the occurrence of the disease. ② Eliminate sclerotia, combining autumn and winter deep plowing to bury sclerotia deeply. When irrigating and preparing the field, before transplanting rice, remove the floating debris containing large amounts of sclerotia. ③ Chemical control, (A) per mu, use 50% thiram wettable powder prepared as a 1500-fold dilution for spraying, or use 150 grams added to 500-1000 kg of water for splashing irrigation; 150-200 grams can also be added to 20 kg of fine soil for broadcasting. (B) Per mu, use 500 grams of validamycin added to 50 kg of water for spraying or splashing irrigation. When applying the pesticide, the rice field should be irrigated with a 2-3 cm deep water layer.