What are the reasons why rice seedlings are slow to tiller?
1. Rice bakanae disease:
Disease pattern and transmission routes: The pathogen of rice bakanae disease overwinters on grains and rice straw. The following year, when diseased seeds or straw are used, the pathogen multiplies as the seeds germinate, invading through the seedling coleoptile or wounds, causing the seedlings to develop the disease and become leggy. Diseased seedlings often wither and die. Diseased seedlings that do not die are pale yellow-green, grow thin and elongated, generally about one-third taller than healthy seedlings; their roots develop poorly, with few tillers or even no tillering. After diseased seedlings are transplanted, they carry the pathogen to the field, causing rice plants to develop the disease. When rice heads and flowers, the pathogen is transmitted by wind and rain to the floral organs, causing grains and straw to carry the pathogen, cyclically infecting and damaging rice. The pathogen readily invades through wounds; sowing mechanically damaged rice seeds, or seedlings with severe root injury, results in more severe disease. Dry-raised seedlings often develop more severe disease than water-raised seedlings.
Control methods: The focus of controlling rice bakanae disease is on seed treatment.
(1) Select disease-free seeds for seed saving. This is a relatively reliable and most effective method.
(2) Strictly disinfect seeds. Soak seeds with strong chlorine essence; or soak seeds with 100 g of 50% carbendazim in 50 kg of water; or soak seeds with 120 g of 35% bakanae-ling in 50 kg of water; or soak seeds in 3% quicklime water for 48 hours. When soaking seeds in the chemical solution, it must be noted that the liquid level must be 15 cm-20 cm above the seed layer for the seeds to absorb. At the same time, during the soaking process, the liquid surface must remain still; it must not be stirred midway, nor reused, to ensure the pathogen is suffocated.
(3) Whether in the seedling bed or the field, diseased plants should be pulled out promptly to prevent further infection.
(4) Properly handle diseased rice straw; it must not be discarded casually, nor piled at the field edges or corners, nor used as a cover for seed germination, nor used to tie seedling bundles. It can be gathered for high-temperature composting, and in severe cases burned.
2. Rice akagare disease:
Rice akagare disease is a physiological disease, commonly known as "red stunted seedlings" or "rust disease." In recent years, the disease has worsened in various places, with affected fields generally suffering a 10-20% yield reduction.
The disease generally begins to occur 10-15 days after seedling transplanting, with a short course of about 1 month and a long course of up to two months. Symptoms are that the seedlings are slow to turn green, or after turning green grow poorly, remain stunted and do not develop, and may even die. The aboveground part of diseased plants is short, with reduced tillering or no tillering. At first the leaf color is dark green, then reddish-brown spots appear along the midvein of the lower leaves and gradually expand, causing the entire leaf to dry up and scorch, looking like a "burned field" from a distance. Rice roots are initially dark brown, then turn black, rot, and smell foul.
The causes of akagare disease are: first, applying too much raw fertilizer, poisoning the rice seedling root system; second, severe soil deficiency in phosphorus, potassium, and zinc, causing nutritional imbalance in the rice plants; third, long-term deep-water irrigation, making the plow layer muddy and rotten, preventing roots from penetrating downward, and causing soil oxygen deficiency; fourth, poor, cold, compacted, and lean soil, resulting in poor development of the rice root system.
Control measures: ① Immediately after seeing the disease, spray Huimanfeng, using 100-125 ml per mu, diluted 500 times with water, and at the same time apply 1 kg of zinc sulfate per mu to degrade toxic substances, enhance root vitality, and promote seedling recovery. ② Increase application of phosphorus, potassium, and zinc fertilizers. For phosphorus deficiency, apply 25 kg of calcium superphosphate per mu; for potassium deficiency, apply 10 kg of potassium chloride or potassium sulfate per mu; for zinc deficiency, apply 1 kg of zinc sulfate per mu. Basal application of phosphorus, potassium, and zinc fertilizers is advocated, because akagare disease mostly occurs at the seedling stage, and basal application is effective. It can also be applied as a topdressing after the disease appears. ③ Drain and expose the field to aerate and increase oxygen. If the rice field has deep floating mud, bubbles, and a foul odor, drain and let it dry slightly in time to improve soil aeration and promote new root growth in the seedlings. ④ Apply organic fertilizer only after it is fully decomposed. ⑤ Vigorously promote straw return to the field.
3. Zinc deficiency
After rice seedlings are transplanted, they are slow to grow, or even fail to turn green, or after turning green do not tiller and even shrink. Farmers generally call this "sitting." "Sitting" fields mostly occur in low-lying, damp areas and cold, rotten, lean fields, but sometimes also occur in fertile fields. There are many reasons for this phenomenon, and zinc deficiency is one very important reason.
The symptoms of zinc deficiency "sitting" in rice are: the leaf tips of the leaves at the base of the rice plant dry up, and yellow-brown to reddish-brown irregular patches appear in the middle section of the leaves, gradually spreading from old leaves to adjacent leaves above. When the disease is severe, the rust spots on old leaves expand into patches and become strip-shaped, the leaf emergence rate slows significantly, newly emerged leaves become smaller, fade and turn white, the plant becomes stunted, and the leaf color fades.
Soils prone to zinc deficiency symptoms mainly include: relatively fertile fields, where calcareous paddy soil with soil organic matter content greater than 1% or with heavy application of green manure is prone to zinc deficiency; strongly leached acidic soils, especially sandy soils with low zinc content, are prone to zinc deficiency; uneven fields that previously showed no zinc deficiency, where during large-scale land leveling in recent years of comprehensive agricultural development, soils that lost much topsoil and low-temperature cold seepage fields are also prone to zinc deficiency; and after many years of phosphorus and potassium supplementation, soils with high available phosphorus content, where heavy application of nitrogen fertilizer increases crop zinc demand, are prone to zinc deficiency.
Zinc deficiency can lead to declines in crop yield and quality, so zinc must be supplemented in time. However, excessive zinc content in the soil can also cause crop poisoning. Therefore, when supplementing zinc in zinc-deficient fields, the amount and concentration used must be strictly controlled; otherwise, it will overcorrect and produce the opposite effect.
The correct method of applying zinc is: when zinc deficiency "sitting" in seedlings is confirmed, use a 0.1%-0.3% zinc sulfate solution and spray the affected rice seedlings 2-3 times consecutively, with an interval of 7 days each time; or apply 1-1.5 kg of zinc sulfate per mu, mix it with dry fine soil, spread it evenly on the field surface, and cultivate the field once by hand. Using the above methods, we successfully solved the zinc supplementation problem for more than 2,000 mu of rice fields, with obvious results.