What are the main diseases of rice at the seedling stage? Read this article to find out

Rice at the seedling stage requires good disease control work to ensure vigorous growth later and the production of high-quality rice ears. What are the main diseases of rice at the seedling stage? How should they be controlled?

1. Main diseases of rice at the seedling stage

1. Bakanae disease

In rice at the seedling stage, diseased seedlings are thinner and taller than healthy seedlings, with slender leaves and leaf sheaths, pale yellow leaf color, and poor root development, and some diseased seedlings die before transplanting. On dead seedlings there are pale red or white moldy powdery substances, the affected internodes are obviously elongated, the nodes are often curved and exposed outside the leaf sheath, and many adventitious fibrous roots grow in reverse from the lower stem nodes, with few or no tillers. When the leaf sheath is peeled open, there are dark brown streaks on the stem, and when the diseased stem is cut open, white spiderweb-like mycelium can be seen, after which the plant gradually dies. When humidity is high, the surface of dead diseased plants is covered with pale brown or white powdery mold, and later black small dots form, which are the fungal perithecia.

2. Bacterial wilt

There are two types of rice bacterial wilt. One is physiological bacterial wilt at the rice seedling nursery stage, which is relatively common and often occurs mixed with damping-off. Its symptom is that the aboveground part of the rice rapidly loses water and dies, and the seedlings remain green when they die; the other is bacterial foot rot occurring in the later stage of the main field, which appears sporadically in the field, even with only 1-2 plants affected in a single clump, and the stem nodes at the base of diseased plants become hard, black, and accompanied by a foul odor. Physiological bacterial wilt mostly occurs around the 3-leaf stage of rice. It is mainly due to low-temperature cold damage, sudden clearing after cold, or excessively large temperature differences, for example, when the film is not removed in time for ventilation and hardening of the seedlings in the rice nursery, causing the seedlings to grow spindly, and after the film is removed, the seedlings cannot adapt to the environment, causing an imbalance in water supply within the seedlings, which in turn causes the aboveground part to rapidly lose water and die.

3. Damping-off

Rice damping-off is caused by Pythium fungi of the Mastigomycotina. The pathogen overwinters in the soil, and after rice is sown, the pathogen begins to infect the seedlings, with the disease being most severe under water-deficient conditions. This disease mostly occurs in dry-raised rice seedling nurseries and is a common major disease in dry-raised rice seedling nurseries. Its symptoms are that after the 2-leaf stage of the seedlings, the leaf tips turn yellow and shrink, root hairs are scarce, and initially it occurs in clusters and patches on the seedbed. After the 4-leaf stage, the symptom is sudden bacterial wilt, with the leaves of clustered and patched seedlings curling lengthwise and wilting, then dying. Low temperature, overcast rain, and insufficient light are important conditions that induce damping-off, among which low temperature has the greatest impact. Under low-temperature conditions, the disease resistance of seedlings decreases, which favors disease occurrence. If the weather remains low-temperature or there is sudden clearing after overcast rain, soil moisture is insufficient, and the physiology of the seedlings is disordered, the disease occurrence worsens.

4. Rice blast at the seedling stage

Rice blast at the seedling stage is a disease induced by seed-borne bacteria and diseased rice straw, and rice blast at the seedling stage begins after the 3-leaf stage of the seedlings. Its symptoms are that the base of the diseased seedling is gray-black, the upper part turns brown, and it curls up and dies; when humidity is relatively high, a large amount of gray-black mold layer is produced on the diseased part. As for disease-inducing factors, it is favorable for disease occurrence under conditions of rain, fog, and dew, and when the temperature is 20°C-30°C, especially 24°C-28°C, with many overcast and rainy days and relative humidity maintained above 90%, it is likely to cause severe occurrence of rice blast.

2. Control of rice diseases at the seedling stage

1. Control method for bakanae disease

At the 1-leaf to 2-leaf stage of rice seedlings, use 50 ml of Qingkulike + 15 ml of garlic oil, dilute with 15 kg of water and spray, once every 5-7 days, for 2 consecutive sprays; 95% Lüheng No. 1 (hymexazol) can also be sprayed for control.

2. Control method for bacterial wilt

The control of bacterial wilt is mainly to ventilate and harden the seedlings in time after the seedlings are full, except on windy days. For water-raised rice seedling nurseries, before strong winds and temperature drops arrive, protect the seedlings by adjusting the water layer. For chemical control, 15% Lifujing can be selected, using 100 g of the agent per mu of seedling nursery, diluted with 50 kg-60 kg of water, and sprayed twice after 3 p.m. on sunny days, with an interval of 7 days; or 1.5 kg of 65% dexon wettable powder, or 2 kg of carbendazim diluted with 60 kg of water can be sprayed or drenched.

3. Control method for damping-off

After low temperature and overcast rain, check the growth of the seedlings in time. If it is found that the leaf tips of the seedlings do not exude water or the seedlings look abnormal, immediately use 25% metalaxyl wettable powder at 0.75 g per sq m or 58% metalaxyl mancozeb wettable powder at 1 g per sq m, diluted with 2 to 2.5 kg of water, and spray or drench on the seedling bed for control.

4. Rice blast at the seedling stage

To prevent rice blast at the seedling stage, generally after the 3-leaf stage of the seedlings, select 40% thiophanate-methyl, 150 g per mu, diluted with 50 kg-60 kg of water, and prevent twice, with an interval of 7 days. It is also possible to use 60 g-80 g of 75% tricyclazole or 100 ml of Fuji No. 1 diluted with 60 kg of water for spraying or drenching.

The above are several diseases that may appear at the rice seedling stage and their control methods. I hope this is helpful to everyone. If you have any questions, please consult the relevant personnel.