Detailed Explanation of Common Rice Diseases and Their Control Methods

Throughout the entire growth period of rice, common diseases include rice blast, bacterial leaf streak, bacterial leaf blight, sheath blight, rice false smut, and others.

(1) Rice blast

Rice can be affected from the seedling stage to the heading stage. According to the symptoms shown by the disease at different growth stages and on different parts, it can be divided into 5 types: seedling blast, leaf blast, node blast, panicle blast, and grain blast.

1. Main symptoms

(1) Seedling blast: The diseased seedling turns grayish-black at the stem base near the soil surface, and the upper part turns light reddish-brown, causing the entire seedling to curl and die.

(2) Leaf blast: It can occur on the leaves of both seedlings and adult plants. There are four different shapes of lesions:

A. Acute-type lesion: generally oval, sometimes irregular; the lesion is dark green, water-soaked, and densely covered with a gray mold layer;

B. Chronic-type lesion: the lesion is brown and spindle-shaped; the outer yellow area is the poisoning part, the inner brown area is the necrotic part, and the central gray area is the collapsed part. When the weather is humid, a grayish-green mold layer forms on the underside of the lesion;

C. Brown-type lesion: the spot is brown and very small, confined between the leaf veins, commonly seen on disease-resistant varieties;

D. White spot-type lesion: the spot is white and nearly round, about the size of 2 to 4 leaf veins.

(3) Node blast: It mainly occurs on the stem nodes and is prone to occur during the jointing stage. At first, brown dots the size of a needle head appear, and later they expand until the whole node or part of the node turns dark brown, the tissue is destroyed, and the stem is easily broken.

(4) Panicle blast: Also called neck blast, commonly known as broken-neck disease, it mainly occurs on the panicle neck and branches. When the panicle neck is affected, the lesion is brown or grayish-black and spreads upward and downward from the panicle neck, reaching up to 3 to 4 cm. When the disease occurs early and severely, it causes white heads. Panicle neck blast often causes the panicle stalk and branches to break.

(5) Grain blast: It mainly occurs on the grains and is brown or dark brown.

2. Occurrence characteristics

The pathogen overwinters on rice straw and diseased grains, and is mainly spread by airflow and rainwater. High temperature and high humidity make the disease more likely to occur. Excessive application of nitrogen fertilizer in the later stage leads to severe disease.

3. Control measures

(1) Select disease-resistant varieties, such as Yixiangyou series, Mian II You 838, and other rice seeds with relatively strong resistance to rice blast;

(2) Seed disinfection: carbendazim, formalin, strong chlorine essence, etc. can be used for seed disinfection;

(3) Strengthen cultivation management by applying fertilizer rationally, paying attention to the combined application of nitrogen, phosphorus, and potassium, maintaining reasonable planting density, and practicing rational irrigation;

(4) Chemical control: rice blast net, tricyclazole, Fuji No. 1, Daokang, Wenke, etc. can be used for spray control, once every 7 days, paying attention to alternating medications, and applying 2 to 3 treatments.

(2) Rice bacterial leaf streak

1. Symptoms: It mainly damages leaves, and sometimes also leaf sheaths. Lesions occur between the leaf veins. At first, they are dark green water-soaked small spots. After expansion, they are restricted by the leaf veins and form dark green streaks that appear transparent against light, about 10 mm long and about 1 mm wide. The surface of the lesions often secretes abundant yellow bacterial ooze, which after drying forms small yellow gum-like particles.

2. Disease characteristics: This pathogen mainly overwinters on rice seeds and rice straw, becoming the primary infection source of this disease. The transmission routes include wind and rain, airflow, and the introduction and export of infected seeds. This disease is a bacterial disease and is one of the major diseases harming rice production. If not controlled in time, it can cause large-scale spread and devastating losses.

3. Control methods: (1) Choose disease-resistant varieties; (2) Seed disinfection: soak seeds with agricultural streptomycin for 2 hours, wash them clean, and then sow; (3) Chemical control: one or two kinds of drugs for preventing bacterial diseases, such as agricultural streptomycin, Caijun, Junduqing, Yekuning, Shidaoling, Keshade, etc., can be used alternately, with 1 to 2 spray treatments, and then control according to the disease condition thereafter.

(3) Rice bacterial leaf blight

Symptoms: There are two types of symptoms: leaf blight type and wilting type. Among leaf blight type symptoms, the most common is that lesions start from the leaf tip or leaf edge, initially as dark green short linear spots, and then spread and expand along both sides, forming long strip-shaped lesions with wavy edges. The wilting type symptoms often occur 3 to 4 weeks after rice seedling transplanting. First, one or two seedlings wilt, then it progresses to all leaves and spreads to other tillers, and finally the whole plant or even the entire clump wilts, loses water, and dies.

Bacterial leaf blight is a bacterial disease, and its control methods are the same as those for bacterial leaf streak.

(4) Rice bakanae disease

Symptoms: This disease can occur from the seedling stage to the heading stage. Diseased seedlings are pale yellow-green in color, grow taller and more slender than healthy seedlings, have narrow and long leaves, and poor root development.

Disease characteristics: The pathogen overwinters on diseased rice grains and straw, or the seeds themselves carry the pathogen, becoming the primary infection source. The pathogen invades the stem base of seedlings through wounds and spreads through irrigation water and rainwater.

Control methods: 1. Select varieties free of disease and avoid saving seeds from diseased fields and nearby fields; 2. Seed disinfection: carbendazim, Quanbaike, strong chlorine essence, etc. can be used for disinfection treatment, and the key lies in disinfection; 3. If diseased plants are found, pull them out immediately.

(5) Rice sheath blight, commonly known as flower-foot stalk disease, rotten-foot blight, etc.

Symptoms: The lesion edge is brown, the center is light brown or grayish-white, and when moist the lesion is grayish-green, water-soaked, and semi-transparent. The lesions develop from the bottom upward.

Disease characteristics: The pathogen overwinters in the soil and directly invades through stomata or lenticels. After rice rows close, high field humidity, excessive planting density, and poor ventilation and light transmission make the disease more likely to occur.

Control methods: 1. Eliminate the source of infection; 2. Maintain reasonable planting density, practice rational irrigation, frequent shallow irrigation, and moderate field drying to reduce field humidity, which can lessen the occurrence of sheath blight; 3. Chemical control: spray with jinggangmycin 3 to 4 times from row closure to before maturity, which can effectively prevent and control the occurrence of sheath blight.

(6) Rice false smut, commonly known as gudan

It damages individual grains. At first, mycelium forms inside the grain and gradually increases, causing the glumes to open and exposing a light yellow block-like substance, namely the pathogen's spore ball.

Control methods: 1. Select disease-resistant varieties; 2. Seed disinfection, the same as for rice blast and sheath blight; 3. In combination with sheath blight control, spray jinggangmycin 3 to 4 times from after row closure to before maturity.

(7) Rice physiological diseases (deficiency symptoms)

Symptoms: They are mainly caused by nutritional imbalance and lack of trace elements. The leaves become variegated and faded, the plants do not tiller well, and after being pulled up there are many black roots and few white roots.

Disease characteristics: They are mainly caused by zinc deficiency. Symptoms are especially obvious in cold-waterlogged fields with poor soil permeability, deep-water irrigation, and poor drainage, where roots are poisoned.

Control methods: 1. In the early stage, practice frequent shallow irrigation and drain the water for field drying; 2. Broadcast or spray zinc sulfate or magnesium-zinc fertilizer at 1 kg per mu.