How to Treat Rice Diseases? A Complete Guide to Practical Control Methods

Rice is one of China's main food crops, widely grown in the southern regions, and also grown in riverside areas in the north. If rice is not managed properly, diseases can occur. So, how do you treat rice diseases?

It depends on what disease the rice has. There are three main diseases, namely rice blast, bacterial leaf blight and sheath blight; other important diseases include rice false smut, bakanae disease, downy mildew and so on. The treatment methods differ for each disease, so they must be handled differently.

1. Rice blast

Rice blast is one of the important diseases of rice, occurring throughout the entire growth period, mainly damaging leaves, stems and panicles. Depending on the period and part affected, it can be divided into seedling blast, leaf blast, node blast, neck blast and grain blast. In epidemic years it generally reduces yields by 10-20%, and in severe cases by 40-50%, or even causes total crop failure.

Control: when the disease occurs, spray 30% kitazin EC at 500 times dilution, 50% xiaojunling water-soluble powder at 500 times dilution, 40% carbendazim suspension concentrate at 500 times dilution, 25% prochloraz EC at 1500 times dilution or other agents for control.

2. Bacterial leaf blight

Bacterial leaf blight occurs mainly on leaves and leaf sheaths. At first, translucent yellow spots appear on the leaf margins, then develop along one or both sides of the leaf margin or along the midrib into wavy yellow-green or gray-green lesions. After a few days the lesions turn gray-white and curl inward, looking withered from a distance.

Control: in the early stage of the disease, spray rice seedlings with 20% flusilazole + prochloraz at 800-1000 times dilution, and observe the changes; depending on the disease severity, apply once every 5-7 days; in the middle stage of the disease, use 20% flusilazole + prochloraz at 1000 times dilution + 2% amino-oligosaccharin at 1200 times dilution, applying once every 5-7 days for 2-3 consecutive applications.

3. Sheath blight

Sheath blight is one of the most common major diseases of rice, occurring from the seedling stage to the panicle stage, most prevalent around heading. It mainly damages leaf sheaths and leaves, and in severe cases invades the stems and spreads to the panicles. It often results in unfilled grains and an increased rate of empty shells, and in severe cases can cause plants to lodge and die.

Control: apply the first treatment when 20-30% of clumps are diseased, and the second treatment after 12-15 days; in dry weather, apply when 40-50% of clumps are diseased.

4. Rice false smut

Rice false smut occurs only on the panicles, damaging some grains. Inside the affected grains, a mycelial mass forms and gradually swells, splitting the lemma and palea and exposing a pale yellow mass, namely the spore cushion, which later covers both sides of the lemma and palea and turns dark green. It is initially covered by a thin membrane, which then ruptures and scatters dark green powder, namely the chlamydospores of the pathogen; on some, black flat sclerotia form on both sides, easily dislodged by wind and rain.

Control: prevention is the priority. The best timings are, first, when the last leaf of more than 1/3 of the stems in the whole field has fully emerged, commonly known as the “boot stage” or “big belly stage” (about 7-10 days before heading), which is the peak period of initial infection by the pathogen; second, at the stage of panicle emergence after the collar breaks, generally applying 3-5 days in advance.

5. Bakanae disease

Bakanae disease occurs in all rice-growing regions nationwide. Mildly affected plants head earlier, with small and unfilled panicles. Grains can also be affected at the heading stage, turning brown in severe cases and failing to set seed, with pale red mold growing in the gaps of the glumes; mildly affected plants show no symptoms, but mycelium is already latent inside.

Control: strictly disinfect seeds, soaking seeds with 100 g of 50% carbendazim in 50 kg of water; or 120 g of 35% emiaoling in 50 kg of water; or soaking seeds in 3% quicklime water for 48 hours.

6. Downy mildew

Downy mildew is severe in the late seedling stage and early main-field stage, damaging rice leaves. On leaves, small yellow-white spots appear at first, then form irregular stripes on the surface, producing a mottled mosaic. The young leaves of affected plants are pale yellow, curled and difficult to emerge, the lower old leaves gradually wither and die, the root system develops poorly, and the plants are stunted. Affected leaf sheaths are slightly soft, with irregular ripples on the surface or becoming wrinkled, brittle and twisted, and tillering is reduced.

Control: in the early stage of the disease, spray 25% metalaxyl wettable powder at 800-1000 times dilution, 90% shuangyijing wettable powder at 400 times dilution, 80% kelü wettable powder at 700 times dilution, 64% sandofan wettable powder at 600 times dilution, 58% metalaxyl · mancozeb or 70% phosethyl · mancozeb wettable powder at 600 times dilution, or 72.2% propamocarb (Previcur) aqueous solution at 800 times dilution.