Major rice insect pests include: the brown planthopper (BPH), several species of stemborers—including those in the genera Scirpophaga and Chilo, the rice gall midge, several species of rice bugs, notably in the genus Leptocorisa, defoliators such as the rice: leafroller, hispa and grasshoppers. The fall army worm, a species of Lepidoptera, also targets and causes damage to rice crops. Rice weevils attack stored produce.
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Rice pests are any organisms or microbes with the potential to reduce the yield or value of the rice crop (or of rice seeds). Rice pests include weeds, pathogens, insects, nematode, rodents, and birds. A variety of factors can contribute to pest outbreaks, including climatic factors, improper irrigation, the overuse of insecticides and high rates of nitrogen fertilizer application. Weather conditions also contribute to pest outbreaks. For example, rice gall midge and army worm outbreaks tend to follow periods of high rainfall early in the wet season, while thrips outbreaks are associated with drought.
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Rice requires slightly more water to produce than other grains. Rice production uses almost a third of Earth's fresh water. Water outflows from rice fields through transpiration, evaporation, seepage, and percolation. It is estimated that it takes about 2,500 litres (660 US gal) of water need to be supplied to account for all of these outflows and produce 1 kilogram (2 lb 3 oz) of rice.
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The worldwide production of rice accounts for more greenhouse gas emissions (GHG) in total than that of any other plant food. It was estimated in 2021 to be responsible for 30% of agricultural methane emissions and 11% of agricultural nitrous oxide emissions. Methane release is caused by long-term flooding of rice fields, inhibiting the soil from absorbing atmospheric oxygen, a process causing anaerobic fermentation of organic matter in the soil. A 2021 study estimated that rice contributed 2 billion tonnes of anthropogenic greenhouse gases in 2010, of the 47 billion total. The study added up GHG emissions from the entire lifecycle, including production, transportation, and consumption, and compared the global totals of different foods. The total for rice was half the total for beef.
A 2010 study found that, as a result of rising temperatures and decreasing solar radiation during the later years of the 20th century, the rice yield growth rate has decreased in many parts of Asia, compared to what would have been observed had the temperature and solar radiation trends not occurred. The yield growth rate had fallen 10–20% at some locations. The study was based on records from 227 farms in Thailand, Vietnam, Nepal, India, China, Bangladesh, and Pakistan. The mechanism of this falling yield was not clear, but might involve increased respiration during warm nights, which expends energy without being able to photosynthesize. More detailed analysis of rice yields by the International Rice Research Institute forecast 20% reduction in yields in Asia per degree Celsius of temperature rise. Rice becomes sterile if exposed to temperatures above 35 °C (95 °F) for more than one hour during flowering and consequently produces no grain.
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