How to carry out reasonable remedial measures after early rice is flooded

Reasonable remedial measures after early rice is flooded

June to July is the rainy season in southern China, and local areas may experience heavy rain or torrential rain, causing flood disasters. Early rice, middle rice and late rice seedling fields may all suffer catastrophic damage. Rice plants in flooded paddy fields have damaged root systems and may even show large numbers of dead seedlings. Corresponding remedial measures should be taken according to the degree of flooding and the growth condition of early rice.

1. Characteristics of flooded early rice

Early rice has different tolerance to waterlogging at different growth stages, shows different symptoms after flooding, and suffers different degrees of loss. After flooding at the seedling stage and tillering stage, thin and weak seedlings are often caused, the basal leaves turn yellow-brown, and leaf collapse occurs after the water recedes, but growth can generally recover. Flooding at the jointing stage of early rice often affects internode elongation; after the water recedes, the internodes are shorter than normal, the plants appear dwarfed, thin and curved, and there are more rotten leaves and black roots. When early rice is flooded at the booting stage, in mild cases the empty grain rate increases and maturity is delayed; in severe cases, spikelets and branches degenerate, causing young panicles to die, white panicles to appear, and serious yield reduction. Flooding at the grain-filling and milk-ripe stages causes most leaves to wither, grains to turn black, some grains to germinate, and the 1000-grain weight to decrease, greatly affecting yield. The effects of flooding are as follows. First, the root system is seriously damaged. The number of black roots and yellow roots in flooded rice increases. According to observations, when conventional indica rice and japonica rice are submerged for 4 days and hybrid rice for 6 days, the proportion of black roots and yellow roots both reaches 100%; when rice is submerged for 10 to 14 days, the proportion of black roots alone reaches 90%, and some roots die. Second, leaves, tillers, main stems and tillering nodes die one after another. The first to die in flooded rice are the leaves submerged in water, and the affected young leaves also die; afterward tillers, main stems and tillering nodes die successively, resulting in missing hills and a serious decline in the total number of seedlings. Third, high-position tillers increase. Surviving rice plants produce tillers along with young leaves, and some even produce tillers on elongated stem nodes. Fourth, the growth period is delayed, and the heading period is prolonged. After rice is flooded, the growth period is delayed; the more days of flooding, the more obvious the delay. Generally, in fields flooded for 3 to 5 days and nights, the full heading stage and maturity stage are delayed by 1 to 2 days; for those flooded for 7 days and nights, the full heading stage and maturity stage are delayed by 2 to 3 days, and in severe cases by more than 5 days. Fifth, yield decreases. Flooded paddy fields have insufficient panicle number; tillers born after the disaster have higher node positions, panicle shape becomes smaller, the 1000-grain weight decreases, and yield declines. In severe losses, the loss can reach more than 80%.

2. Remedial measures

The main measures are as follows: 1) Quickly drain the accumulated water. After flooding occurs, forces should be organized immediately to drain water as quickly as possible so that early rice seedlings emerge from the water as soon as possible and the flooding time is reduced as much as possible. In the drainage process, drain high-bank fields first and low-lying fields later. On cloudy and rainy days, the field water can be drained completely in one go. If few plants in the field have collapsed leaves, the seedlings grow robustly, and there is much floating mud in the field, drainage can be combined with exposing the field to prevent seedling lodging. If drainage occurs under bright sunny weather, then when the temperature is high the drainage speed should be slowed, and an appropriate shallow water layer should be retained in the field; draining completely in one go can easily cause bacterial wilt and dead seedlings, resulting in greater losses. 2) Timely remove mud and sand. After early rice is flooded, stems and leaves are often covered with mud and sand, causing leaf collapse or lodging. To help the seedlings recover growth as soon as possible, forces should be organized to carry away the mud and sand accumulated in the field as early as possible and fish out floating debris, so as to reduce the degree of crushing injury to the seedlings. At the same time, a bamboo pole should be used to sweep back and forth to knock the mud and sand off the stems and leaves. When the water recedes and the seedling tips are exposed, wash the seedlings with clean water. After the water recedes, straighten lodged seedlings and remove rotten leaves and yellow leaves. 3) Open ditches at the proper time to control water. After the accumulated water in the paddy field recedes, the field moisture is still in a saturated state, so ditches should be opened for drainage so that water in the field soil seeps into the ditches and is discharged, lowering the field water content as soon as possible and allowing the floating mud formed by flooding to gradually settle and consolidate, thereby promoting the growth of new roots. Adhere to an alternating dry and wet irrigation method, which not only ensures the water needs of the rice plants but also ensures soil aeration and promotes a large number and strong vitality of roots at the upper nodes. If low temperature is encountered at the heading stage, deep water irrigation should be adopted; in the late stage of grain filling and ripening, take care to avoid stopping water too early. 4) Increase the application of quick-acting fertilizers. During flooding, the vegetative organs of early rice are damaged to varying degrees. After emerging from the water, roots, leaves and tillers resume growth and require large amounts of mineral nutrients. In addition, the original fertilizer in the paddy field is lost in large amounts. At this time, a combination of root topdressing and foliar topdressing should be adopted, applying quick-acting fertilizers. Topdressing should be fast and the amount sufficient to promote the rice plants to recover growth as soon as possible. After drainage, apply 5 kg and 6 kg of urea and potassium chloride respectively per mu (1 mu = 667 sq m, the same below) to the early rice field, mix evenly and broadcast. A 0.3% potassium dihydrogen phosphate solution at 50 kg can also be used for foliar spraying 1 to 2 times to meet the nutrient needs of the rice plants, improve leaf photosynthetic function, and promote the seedlings to recover growth as soon as possible. 5) Strengthen the prevention and control of diseases and insect pests in flooded early rice. After early rice is flooded, because the disease resistance of the plants decreases and the field easily forms a microclimate of high temperature and high humidity, this is conducive to the occurrence and spread of diseases and insect pests, and most easily causes the occurrence and epidemic of bacterial diseases such as bacterial brown stripe disease and bacterial leaf blight. Therefore, it is necessary to persist in rational fertilization and irrigation, strive to separate drainage and irrigation, prevent cross-irrigation among early rice fields, and achieve frequent irrigation with shallow water. Control nitrogen fertilizer application and appropriately increase phosphorus and potassium fertilizer to enhance plant disease resistance. For old disease areas and flooded paddy fields where bacterial leaf blight and bacterial brown stripe disease first occur, chemical control should be carried out in a timely manner. For affected plots, 20% Yeqingshuang wettable powder at 100 to 150 g per mu can be used, diluted with 50 kg of water, or 97% strong chlorine wettable powder at 100 g per mu, diluted with 50 kg of water, for spray control. When spraying, it is required to be uniform and comprehensive, and to spray enough of the required medicinal solution, so as to promptly control the spread of bacterial diseases. In addition, the leaves and tillers born after flooded early rice resumes growth are relatively tender and green and are susceptible to damage by the rice leaf roller. In particular, after flooded early rice resumes growth, the leaf color is tender and green, and the growth period is often delayed, making it most likely to encounter outbreak damage by the second generation of the rice leaf roller, causing large numbers of white leaves and greatly affecting early rice production. Key control should be carried out against the second generation of the rice leaf roller. Effective insecticides that can be selected include abamectin, emamectin benzoate, tetrachlorantraniliprole, chlorantraniliprole, indoxacarb, etc. In addition, because the growth and development period is delayed, opportunities for invasion by the rice planthopper and the striped stem borer increase, so insect conditions must be grasped in a timely manner for control. In the late growth stage of flooded early rice, if there are many cloudy and rainy days, close attention should also be paid to the occurrence and control of rice blast, especially panicle neck blast. Effective agents that can be selected include biological pesticides such as Bacillus subtilis, polyoxin and kasugamycin, as well as chemical pesticides such as tricyclazole and prothioconazole.