How to prevent and control rice false smut? Key technical points explained in detail

Rice false smut is a rice disease with a wide range of damage, occurring in all major rice-producing regions of the world, and both northern and southern rice in China are affected by it. After rice false smut occurs, the rice becomes moldy and the rate of empty and shriveled grains increases, thereby affecting grain quality, reducing commercial value, and affecting human health. So how can it be prevented and controlled?

Prevention and control methods for rice false smut

1. Select high-yield, disease-resistant varieties: generally, loose-panicle and early-maturing varieties have milder incidence; dense-panicle and late-maturing varieties have more severe incidence. For example, select new varieties Chujing 28 and Yunjing 26.

2. Remove diseased residues: diseased grains found early should be picked off promptly; after harvest in heavily diseased fields, deep plowing should be carried out so that sclerotia and smut balls rot in the soil; before spring sowing, clean up field debris to reduce sources of inoculum.

3. Fertilize scientifically and reasonably: where conditions permit, field fertilization should be based mainly on farmyard manure and organic fertilizer, with nitrogen, phosphorus, and potassium fertilizers used in combination; do not apply excessive or late nitrogen fertilizer.   

4. Scientific water management: field water management should be carried out scientifically according to the water requirements of rice growth, that is, shallow water for transplanting, one-cun water for regreening, thin water for tillering, drying the field when enough seedlings have developed, one-cun water to promote heading, and moist conditions to plump the grains.

5. Chemical control: 7-10 days before rice heading (the booting stage) and at the full heading stage, use 100 grams of 40% dimethachlon or 100 grams of 20% jinggangmycin per mu, mixed with 60 kg of water, and spray evenly twice to control rice false smut.

What is rice false smut?

Rice false smut is an important disease that occurs on the panicle in the late growth stage of rice. This disease mostly occurs in years with a good rice harvest and is often mistaken by farmers as a sign of a bumper year, so it is called the “bumper harvest fruit”. Rice false smut mainly infects during the heading and flowering stage. The pathogen damages some grains on the panicle. Usually there are one to several grains affected on a panicle, and in severe cases more than a dozen.

At first, a pale yellow-green block-like substance appears at the seam of the glumes, gradually swells, and finally covers the entire glume shell. It is 3—4 times larger than a healthy grain, dark green, with a smooth surface, then cracks, showing a cracked-like pattern, and releases dark green powder, which is the thick-walled spores of the pathogen.

Rice false smut not only destroys the diseased grains, but also consumes the nutrients of the entire diseased panicle, causing other grains to be unfilled. As the number of diseased grains increases, empty and shriveled grains rise markedly, the 1000-grain weight decreases, and rice quality declines severely. The toxins produced by rice false smut contaminate rice. After humans and livestock consume it, poisoning can occur, seriously harming human and livestock health. In recent years, in Hongta District, due to the increase in the area planted with high-quality rice and continuous rainy weather during the rice heading and flowering stage, rice false smut has occurred to varying degrees.

Symptoms of rice false smut damage

Rice false smut is a fungal disease that occurs only on the panicle. After the pathogen invades the grain, it forms a mycelial mass inside the glume. After destroying the internal tissues of the diseased grain, the mycelial mass gradually enlarges. First, a pale yellow-green block-like spore cushion is exposed from the seam of the inner and outer glumes, then it turns dark green or olive-colored, wraps the glume, is nearly spherical, and its volume can reach several times that of a healthy grain. Finally, the surface of the spore cushion cracks and scatters dark green powdery thick-walled spores.

When a diseased grain is cut open, the center is a white fleshy mass composed of mycelial tissue, and the outer part can be divided into 3 layers: the outer layer is the earliest-matured thick-walled spores, dark green; the middle is mycelium and gradually maturing thick-walled spores, orange-yellow; the inner layer is radial mycelium and thick-walled spores in the process of formation, pale yellow. In the late stage of disease, 2-4 black, slightly flattened, hard sclerotia may form on both sides of some spore cushions. The sclerotia easily fall off into the field and overwinter.

Causes of rice false smut occurrence

The epidemic of rice false smut mainly depends on factors such as the amount of sclerotia in the field, the susceptibility of varieties, the coincidence of the rice heading stage with the period of sclerotial germination and spore spread, and the rain and humidity coefficient during the heading stage.

1. Host resistance: under natural conditions, the resistance and susceptibility reactions among varieties differ significantly. Late-heading varieties tend to have major outbreaks. Japonica rice is more severely affected than indica rice, and hybrid rice is more severely affected than conventional rice. Diseased grains mainly occur in the middle and lower parts of the panicle, followed by the upper part; large-panicle and dense-panicle varieties with many stem grains have a high incidence. Varieties with slow heading rate and a long heading period also have a long disease period and severe incidence.

2. Environment: when heading and flowering encounter abundant rain and low temperature, especially continuous overcast rain, the incidence is severe. During the rice flowering stage, an average daily temperature of 25-28°C and 3-5 consecutive overcast and rainy days easily induce this disease.

3. Cultivation: ① In fields with severe incidence in the current year, because the amount of seed-borne inoculum in the field is large, the incidence may be severe the following year.

② Excessive application of nitrogen fertilizer and excessive use of panicle fertilizer, without applying phosphorus and potassium fertilizer, cause severe field shading, poor ventilation and light transmission, and high relative humidity, all of which aggravate the occurrence of the disease.

③ Flooding, continuous irrigation, and flood irrigation are important reasons for the spread of rice false smut. Near water inlets, field edges, and improper field management, with water drained too late in the later stage, result in severe incidence.

The above is our introduction to rice false smut. We have learned about the causes of the disease and prevention and control methods. In order to ensure the rice harvest, everyone must pay attention to preventing the occurrence of some insect pests and diseases, and must continuously learn techniques to achieve high and high-quality yields. We also wish everyone a good harvest here.