Unlike other pests, rice grain smut is caused by many factors. Therefore, finding the cause and preventing rice grain smut causes many difficulties for farmers.

What is rice grain smut?

Rice grain smut is the general name for the phenomenon of rice grains being half-shelled (with very little rice inside) or being empty (with no rice inside at all). When rice grains are smut, it may be accompanied by symptoms of discolored hulls and rice grains depending on the pathogen. Rice grain smut not only reduces yield but also reduces the quality of rice grains, causing economic losses to farmers.

When does grain rot appear?

The most susceptible period is from the flowering stage to the milky maturity stage, which falls in the months with low temperatures, high humidity, high rainfall and many rainy days. It is difficult for any rice variety or crop to avoid the harmful effects of grain smut, the only difference is in the severity depending on weather conditions and the ability to control and prevent the disease. If the rice is smut early and meets favorable weather conditions for the disease to develop and farmers do not spray pesticides in time, the rate of half-sucked grains will be very high, causing great losses in yield.

What causes grain bulge?

There are many factors that cause grain smut. Timely and correct detection of the cause of the disease will help farmers choose effective prevention measures. There are 3 main causes of grain smut in rice:

1. Fungal grain rot

Currently, there are more than 11 different types of fungi that cause grain smut in rice such as Pyricularia oryzae, Alternaria padwickii, Tilletia barclayana, Bipolaris oryzae, Phoma sp, Ustilagonoides virens... Among the causes of grain smut in rice, fungi are the most important factor.

Black smut is a sign of rice grain smut caused by fungi. Fungi that cause damage to grains have purple to dark purple, light brown to dark brown spots. When the humidity is high, these colors will be covered with a layer of white powder on the outside.

2. Bacterial grain rot

The bacteria that causes rice grain to be smutty is Pseudomonas glumae (or Bukhoderia glumae) which survives from the previous crop or exists in soil and water. When rice is infected, the grain will rot black or have diseased spots on the grain shell.

Yellow smut is a symptom of the disease caused by bacteria. When the rice blooms, the husk opens, and the bacteria will attack the inside of the rice grain. The spikes with infected rice grains that cannot be pollinated will be smutty, the husk will not change color or will be yellow or light green. When the grain is firm, the branches that are not infected will be heavy and bent down. On the contrary, the diseased branches will stand straight, which is often called shooting airplanes. When separating the husk of the diseased grain, the endosperm will be rotten and cannot enter the rice grain.

3. Seed rot caused by insects (spider mites)

Rice panicle mites usually live in the leaf sheaths. When the density of mites increases, they can crawl up the rice panicles and suck the developing rice panicles, causing the rice to grow upright and most of the grains to be empty.

Prevention measures

- Select rice varieties that are resistant to pests and diseases; treat seeds before planting.

- Soak and wash away salt, detoxify the soil;

- Plant at the right time with appropriate planting density;

- Fertilize adequately and in balance, provide additional medium and micronutrients; effectively prevent insects, spider mites and other harmful diseases.

- In fact, the main cause of rice grain sterility is caused by microorganisms and spider mites. Therefore, when weather conditions are suitable for diseases and spider mites, spray chemicals specifically for each type of pest; when the disease appears, maintain a water level of 2-3 cm on the field surface; then immediately use pesticides in the List of pesticides permitted for use in Vietnam to spray to prevent diseases...

Note: Using plant protection drugs (PPE) to spray to control diseases is most effective 3-5 days before and after rice flowering when microorganisms have not yet parasitized the rice panicles. At the same time, it is necessary to spray early, when the disease has just begun to cause damage; use PPE according to the "4 rights" principle; should rotate the drugs between sprays, need to spray thoroughly on the rice stalks and panicles; spray in the cool afternoon to avoid affecting the drying process of the rice.