Latest Technical Methods Tutorial for the Prevention and Control of Rice Seedling Blight

Rice seedling blight is one of the most important diseases of dry-raised rice seedlings. Its main causes are excessively low temperatures, excessive day-night temperature differences, alkaline soil, insufficient light leading to weak and spindly seedlings, and excessive seeding rates. The main field symptoms are wilting of seedlings after emergence, easy breaking when pulled, rotting at the base of the stem, a rotten pear smell, and in severe cases the entire patch dies off. Diseased plants often have reddish mold-like growth at the base.

Occurrence Period of Rice Seedling Blight

When seedlings are at the 2-3 leaf stage, the endosperm is nearly exhausted, and cold resistance is at its weakest. When the daily average temperature falls below 12-15~C, growth is impeded, disease resistance is significantly weakened, and pathogens easily invade. At this time, if low temperatures and overcast rain occur, seedling blight is most likely to develop. Therefore, the 2-3 leaf stage of dry-raised seedlings is the main period for seedling blight epidemics.

Harmful Symptoms of Rice Seedling Blight

1. Bud rot: occurs before emergence or just as seedlings emerge. The young buds or young roots of seedlings turn brown, and diseased buds twist, rot and die. Mold layers form on the seeds or at the base of the buds.

2. Needle rot: mostly occurs from the needle stage to the 2-leaf stage. The central leaf of diseased seedlings turns yellow and withered, leaves do not unfold, the base turns brown, sometimes brown spots appear on the leaf sheath, and diseased roots gradually turn yellow-brown. Mold layers form at the junction between the seed and the seedling base, the stem base is weak and easily broken, and seedlings in the seedbed often occur and die in clusters and patches.

3. Yellow wilt and green wilt: mostly occur around the 2.5-leaf stage. Diseased seedlings do not exude water from leaf tips, leaf color turns yellow and withered, and they wilt, rapidly expanding outward in patches. The base and roots of seedlings break off very easily, and leaves curl. When the weather suddenly clears, seedlings rapidly show green wilt, with the central leaf and upper leaves “curling”. The seedling leaves remain green, and finally the whole plant wilts. After transplanting, patches of green withered and dead plants appear in the main field.

Causes of Rice Seedling Blight

1. Climatic conditions: low temperature, overcast rain and insufficient light are important conditions that trigger seedling blight, among which low temperature has the greatest impact. Under low temperature conditions, seedling disease resistance decreases, which favors disease occurrence. Excessively low temperatures have little effect on pathogen development and infection, but are unfavorable for seedling growth, causing poor root development and reduced nutrient uptake capacity, which further promotes disease development. If the weather remains low temperature or suddenly clears after overcast rain, soil moisture is insufficient, seedling physiology is disrupted, and disease occurrence worsens.

2. Infection cycle: rice seedling blight is a soil-borne disease. It is caused by infection by multiple pathogens, mainly including Fusarium oxysporum, Fusarium graminearum, Fusarium equiseti, Fusarium solani, Fusarium moniliforme of the genus Fusarium, order Tuberculariales, subdivision Deuteromycotina, as well as Rhizoctonia solani of the genus Rhizoctonia, order Mycelia Sterilia, and Pythium spp. of the genus Pythium, order Peronosporales, subdivision Mastigomycotina, among other fungi. Fusarium generally overwinters as mycelium and chlamydospores in the diseased residues of various hosts and in soil. When environmental conditions are suitable, it produces conidia that spread through airflow and cause infection and damage. Rhizoctonia overwinters as mycelium and sclerotia in host diseased residues and in soil, and spreads among seedlings by mycelial growth to cause infection and damage.

3. Seedling quality: pathogens of rice seedling blight such as Rhizoctonia and Fusarium are widely present in soil and are all weak parasites, generally able to live saprophytically in water or soil. These pathogens are not highly pathogenic and generally do not readily infect healthy and vigorous seedlings. Only when adverse weather and improper management cause seedlings to grow weakly and resistance to decrease do various weak parasites take the opportunity to invade and spread. Therefore, poor seedling quality, weak growth, and poor disease and stress resistance are the direct causes of seedling blight occurrence.

Integrated Prevention and Control of Rice Seedling Blight

Prevention and control of seedling blight should focus on prevention, combining prevention with control.

1. At the 1-2 leaf stage of rice seedlings, use 50ml of Aolike (Qingku Lijing) + 15ml of garlic oil, dilute with 15 kg of water and spray, once every 5-7 days, for 2 consecutive sprays. To enhance plant disease resistance, it is recommended to add 25ml of foliar fertilizer (Wofengsu) per 15 kg of water when spraying. In the middle to late stages of disease: use 100ml of Aolike Qingku Lijing + 15ml of garlic oil for spraying, once every 3 days, for 2 to 3 consecutive sprays.

2. Carefully select seeds and sun-dry them. Improve germination techniques, prevent seed injury, and enhance seed vitality and disease resistance.

3. Sow at the appropriate time, and do not sow too densely. Sow when the temperature steadily passes 6°C; do not blindly rush to sow early. Theoretically, the sowing density should be 300 g/m2. However, in actual production, farmers often increase the seeding rate in order to save on production costs such as agricultural film, as well as considering germination rates and the use of rice transplanters. Even so, the seeding rate must absolutely not exceed 500 g/m.

4. Seedbed management. Do a good job in cold protection, heat preservation, ventilation, and seedling hardening, improve seedling disease resistance, and prevent and reduce the occurrence of seedling blight and bakanae disease.

5. Strengthen field management. Do a good job in cold protection, heat preservation, ventilation, and seedling hardening. Achieve early protection (heat preservation before emergence), mid-stage control (temperature control from emergence to the 3-leaf stage), and late hardening (temperature regulation from the 3-leaf stage to before transplanting). Advocate sparse transplanting and early seedling raising, and control temperature and humidity to prevent excessive growth. At the 1-leaf-1-heart stage, maintain a temperature of 25-30~C and water as little as possible. After the 2nd leaf stage, seedlings must gradually adapt to cold conditions. At the 3-leaf-1-heart stage, the temperature should not exceed 25°C, and soil moisture should be sufficient but not overly wet. After the 3-leaf stage, the film should be uncovered during the day for ventilation and hardening. At night, if there is no frost, it is best to also uncover the film so that seedlings experience low temperatures. This can cultivate strong seedlings with high cold resistance.

6. For seedbed soil disinfection, spray with 300-fold dilution of 3.2 e-jia aqueous solution; soak seeds with Guangmieling aqueous solution for 24-48 h, or spray with 500-1000-fold dilution at the 1-leaf-1-heart stage. At the 1-leaf-1-heart stage of rice seedlings, spray each tray with 0.9 g of 15% Likuiling liquid diluted in 1 L of water. Spray with 500-fold dilution of 70% Dexon powder or 1% ammonium sulfate, and pay attention to maintaining seedbed soil moisture to effectively prevent the harm of seedling blight. In the early stage of seedling disease, apply Likuqing at 1-1.5 g per square meter, mix with water and spray evenly on the seedbed.