Rice planting and management in China

Rice is the largest food source in China and 65% of the population survive on it. According to the National Bureau of Statistics, in 2019, the rice plantations in China measured 29.694 million hectares, accounting for around 30% of the total growing area of food crops. In 2019, the yield per hectare of rice was 7059 kg/ha, which is 32.4 kg/ha higher than the figure in 2018 and recorded another high in history. The annual total output reached 209.61 million tons, maintaining a level of over 200 million tons for nine consecutive years, accounting for about 40% of the total grain output.

According to statistics, in 2019, China imported 2.55 million tons of rice, a year-on-year decrease of 530,000 tons or 17.2%. The main sources were still Southeast Asian and South Asian countries such as Vietnam, Thailand, Pakistan, Myanmar and Cambodia. Also in this year, China exported 2.748 million tons of rice, a year-on-year increase of 659,000 tons or 31.5%, and the main destinations were Cote d'Ivoire, Egypt and other African countries. The year 2019 also witnessed rice exports overtaking imports and achieving a net rice export for the first time since 2011.

Strategies for the control of diseases, pests and weeds in rice

The management strategies for diseases, pests, weeds and nutrition in growing of rice is differentiated, subject to different rice varieties, growing modes (direct seeding in water, direct seeding in a dry field, seeding in a dry field and cultivating in water, artificial seedling throwing, mechanical transplanting, etc.), climatic conditions and soil properties. 

However, there is also something common among them. In China, rice blast, sheath blight, rice false smut, brown streak, bacterial root rot and white leaf disease are the main rice diseases. Rice sheath blight and rice blast occur in six provinces along the Yangtze River generally to a moderate degree, and rice false smut outbreaks are severe all year round in some areas, while fairly severe bacterial streaks appear during some years. 

Rice leaf folder, white-backed planthopper, brown planthopper, smaller brown planthopper, stem borer, yellow stem borer, etc. are the main pests, among which rice leaf folder outbreaks are severe every year in some provinces, and the fairly severe stem borer, which has developed resistance to various agrochemicals, occurs in hybrid rice-growing areas all year round. 

Besides, rice also faces the invasion of broadleaf weeds, Cyperaceae weeds, various barnyard grass and other weeds. In paddy fields, there exist challenges of large weed population, expanding resistant weeds, inferior effect in stem and leaf treatment in the later stage, and an increasing amount of weedy rice, etc.

To reduce use of chemicals and increase efficiency of chemical control, China is gradually adopting a technical strategy of lessening and simplifying the use of pesticides for rice, and a scientific prevention and control strategy with “prevention” as the core and “control” as the support.

To tackle the issue of weeds in paddy fields, such as direct seeding field (the method is different in transplanting rice), a weeding mode of “Pre-emergence weeding + Post emergency weeding + Supplementary weeding” has been mainly adopted, which reduces the weed population in the early stage and kills the weeds in the middle and late stages. 

Pre-emergence weeding mainly refers to the use of herbicides with wide herbicidal spectrum and good soil treatment effect to contain the first peaking of weeds by making use of the soil potential difference between weeds and rice seeds after seeding and before emergence. Post emergency weeding refers to weeding operations around the 3-leaf stage of rice and the 2-3-leaf stage of weeds, which is a critical period for rice weeding, including controlling the remaining older weeds of the early stage and effectively containing the occurrence of the second peak of weeds. Supplementary weeding refers to clearing malignant weeds and remaining weeds of the second weeds occurrence peak with selected herbicides 30-35 days after seeding.

For the prevention of rice diseases and pests, preventative measures, that is seed treatment before seeding, transplanting with pesticides applied and pesticide application for rice panicle protection before breaching, are the keys to solve these problems, for which, no control indicators are specified, the decision-making process for pesticide application is simplified and the application time is shifted forward.

Seed treatment is an important way to reduce pesticide use and improve efficiency. According to statistics, in 2018, the crop growing area after seed treatment reached 1 billion mu in China, accounting for 45% of the cultivated area and 12.5% of the disease and pest control area nationwide. The active ingredients of rice seed treatment agents are mainly insecticides, fungicides and the mixture of insecticides and fungicides. Compared to its ratio of 15-20% in pesticides in developed agricultural countries, seed coating accounts for only 5% of the total in China, representing a good development potential.

Before transplanting, the application of pesticides on the seedling tray can effectively prevent and control rice diseases and pests, and the lasting period can reach 50-60 days in some regions. Application on seedling trays can avoid premature application infield, and greatly reduce labor input and application times infield. One day before transplanting, spraying or spreading pesticides (preferably long-lasting, slow-controlled release granules) evenly on seedling trays can prevent diseases and pests for 40-50 days after transplanting. High use of pesticides in the seedling stage can improve the prevention and control effect against diseases and pests, reduce the use of pesticides and save labor. However, attention should be paid to the development of resistance. Taking the control of rice stem borer as an example, the resistance of the pest population to organophosphorus pesticides, such as chlorpyrifos, is at a medium level in Zhejiang, Jiangxi and Hunan provinces, with a resistance multiple of 12-64 times. The resistance to diamides, such as chlorantraniliprole, is at a moderate to high level in Zhejiang, Jiangxi, Hunan and other provinces, with a resistance multiple of 13-259 times.

Major diseases in the later stage of rice include ear neck blast, false smut, ear rot, sheath blight, bacterial blight, bacterial leaf stripe, ear blight, etc. Among them, rice false smut, rice blast, ear rot and other diseases can only be prevented, instead of being treated (there is almost no control effect after the disease appears). Therefore, it is very important to find the best time to control these diseases. Applying pesticides during rice breaching (that is heading of 5%-10% plants) can effectively control false smut and rice blast, and is also beneficial to the growth of rice so that the stalks and leaves can stay green in the later stage of rice when it becomes ripe naturally and the yield can be increased. The specific application time before breaching is generally based on the main targets to be prevented. A lasting period of 20-30 days is required for the control of disease in booting stage.

Scientific management system helps China achieve designed targets

Rice is the food crop with the largest pesticide consumption in China, accounting for 18% of the total. The registrations for rice account for about 20% of pesticide varieties. In 2019, China’s Ministry of Agriculture and Rural Affairs issued an indicator system for green rice varieties, to guide the cultivation of green rice varieties with “less use of pesticides and chemical fertilizers, water-saving, drought resistance, high quality and high yield”, and accelerating the upgrading of green varieties.