Common Rice Diseases and a Detailed Guide to Chemical Control Methods

Rice is a species of the grass genus Oryza, and it is also the most important and longest-cultivated species in the genus used as a food grain. It is a direct cash crop.So what are the common rice diseases? What chemicals should be sprayed? How should they be controlled?Let's take a look below.

Throughout its entire growth period, rice can be affected by many diseases, but the common diseases include rice blast, bacterial leaf streak, bacterial leaf blight, sheath blight, and rice false smut.

I. 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 stem base of diseased seedlings near the ground turns grayish black, while 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 gray mold.

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

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

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

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

(4) Panicle blast: also called neck blast, 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 in length. When the disease occurs early and severely, it causes white heads, and neck blast often causes the panicle stalk and branches to break.

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

2. Occurrence characteristics

The pathogen overwinters on rice straw and diseased grain and is mainly spread by airflow and rainwater. High temperature and high humidity make the disease likely to occur, and excessive nitrogen fertilizer applied later in the season makes the disease more severe.

3. Control measures

(1) Select disease-resistant varieties.

(2) Disinfect seeds. Prochloraz can be used for seed soaking, with each 10 ml mixed with 20 kg of water (2000-fold solution) for soaking.

(3) Strengthen cultivation management by applying fertilizer reasonably, paying attention to the combined application of nitrogen, phosphorus, and potassium, maintaining reasonable planting density, and irrigating properly.

(4) Chemical control: 75% tricyclazole wettable powder 30 to 50 g per mu can be used, mixed with 45 kg of water, and sprayed evenly for control.

II. Rice bacterial leaf streak

1. Symptoms mainly damage leaves and sometimes leaf sheaths. The lesions first appear as dark green water-soaked small spots. After expansion, they are limited by leaf veins and form dark green streaks that appear transparent against light. The surface of the lesions often secretes abundant yellow bacterial ooze, which after drying forms small yellow gum-like particles.

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

3. Control methods: (1) Select disease-resistant varieties. (2) Disinfect seeds by soaking them in agricultural streptomycin for 2 hours, then washing them clean before sowing. (3) Chemical control: agents for controlling bacterial diseases such as agricultural streptomycin and leaf blight ning can be used alternately, sprayed 1 to 2 times for control, and then controlled later according to disease development.

III. Rice bacterial leaf blight

1. Symptoms are divided into two types: leaf blight-type symptoms and wilt-type symptoms. Among leaf blight-type symptoms, the most common is that the lesion starts from the leaf tip or leaf margin, initially as a dark green linear short streak, and then spreads and expands along both sides, forming a long strip-like lesion with wavy edges. Wilt-type symptoms often occur 3 to 4 weeks after transplanting seedlings; first one or two young leaves wilt, then it develops to all leaves and spreads to other tillers, and finally the whole plant or even the whole clump wilts, loses water, and dies.

2. Control methods: for chemical control of bacterial leaf blight, use 20% thiodiazole-copper suspension concentrate 60 g to 80 g per mu, mixed with 45 kg of water, and spray evenly for control.

IV. Rice bakanae disease

1. 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.

2. Occurrence characteristics: the pathogen overwinters on diseased rice 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.

3. Control methods: (1) Select disease-free varieties and avoid saving seeds from diseased fields and nearby fields. (2) Disinfect seeds with carbendazim, prochloraz, and other agents for seed treatment. If diseased plants are found, pull them out immediately.

V. Rice sheath blight

1. Symptoms: the lesion edges are brown, and the centers are light brown or grayish white. When moist, the lesions are grayish green, water-soaked, and semi-transparent. The lesions develop from the bottom upward.

2. Occurrence characteristics: the pathogen overwinters in the soil and directly invades through stomata or lenticels. After the rice canopy closes, high field humidity, excessive planting density, and poor ventilation and light penetration make the disease likely to occur.

3. Control methods: (1) Eliminate the source of inoculum. (2) Maintain reasonable planting density, irrigate reasonably, irrigate frequently with shallow water, and dry the field moderately to reduce field humidity, which can reduce the occurrence of sheath blight. (3) Chemical control: from canopy closure to before maturity, use 4% validamycin · 1.6 billion Bacillus cereus 48 g per mu, mixed with 45 kg of water; alternatively, use 30% hexaconazole suspension concentrate 20 g per mu, mixed with 45 kg of water, and spray for control.

VI. Rice false smut

1. Symptoms damage individual grains. At first, mycelium forms inside the grain and gradually enlarges, causing the lemma and palea to open and expose a pale yellow mass, namely the pathogen's spore ball.

2. Control methods: (1) Choose disease-resistant varieties. (2) Disinfect seeds, the same as for rice blast and sheath blight. (3) In combination with sheath blight control, spray validamycin 3 to 4 times from canopy closure to before maturity.