Overall, diseases and pests in mid- to late-season rice are expected to occur at moderate levels, with an estimated affected area of 970 million mu‑times.

Release Date:

2018-07-14

　　On July 10–11, 2018, the National Agricultural Technology Extension Center convened a consultation meeting in Songyuan, Jilin, to assess the trends in the occurrence of diseases and pests affecting mid- to late-season rice and autumn locusts. Based on a comprehensive analysis of current pest and disease populations, cropping conditions, and climatic factors, technical personnel from plant protection agencies in 19 major rice-producing provinces, autonomous regions, and municipalities directly under the central government, along with relevant experts, projected that major rice diseases and pests would generally occur at moderate levels, affecting a total area of 970 million mu‑times. Specifically, brown planthoppers are expected to be moderately severe in the rice-growing areas of South China, the Jiangnan region, and eastern Southwest China; stem borers will be moderately severe in the lower Yangtze River rice region; and two-brooded stem borers will be moderately severe in the Jiangnan and northern Southwest rice regions, with a combined affected area of 640 million mu‑times. Meanwhile, sheath blight is anticipated to be moderately severe across most southern rice areas, while blast disease will be moderately severe in the northern Southwest, the middle and lower reaches of the Yangtze River, and localized areas in Northeast China, covering a total affected area of 330 million mu‑times.
　　1. Overview of Early-Season Diseases and Pests and the Early Stages of Single-Cropping Medium-Ripening Rice
　　In the first half of this year, major rice pests and diseases occurred at a generally moderate level across southern rice-growing regions, affecting 358 million mu‑times, a 2.5% decrease compared with the same period last year. Among these, pest outbreaks accounted for 266 million mu‑times, up 0.4% year on year, while disease outbreaks totaled 91.71 million mu‑times, down 10.1% year on year. The key characteristics of these outbreaks are as follows.
　　Stem borers have generally occurred at moderate levels, lighter than last year. Specifically, the Jiangnan and middle Yangtze rice‑growing regions experienced relatively mild infestations; the central and eastern parts of South China and the southwestern rice‑growing areas saw moderate outbreaks; while western South China faced more severe attacks, with localized, poorly managed fields suffering heavy damage. Nationwide, the cumulative affected area totaled 92.73 million mu‑times, down 8.2% year on year. According to monitoring across regions, this year’s migratory influx of stem borers began earlier than last year but was close to the long-term average; in the southwest and the middle Yangtze rice‑growing areas, the onset was 3–14 days earlier than in 2022. However, the number of migration peaks was fewer, and the overall influx of pests remained low. As of July 5, data from 304 rice‑monitoring stations under the National Pest and Disease Forecasting Network show that the total migratory influx of stem borers reached its lowest level in the past five years—down 44.1% year on year and 56.5% below the five‑year average. In some local areas, the influx was notably higher: for example, Hubei recorded a total influx 88.6% greater than the same period last year and 73.9% above the five‑year mean. Field populations were generally low, though locally elevated in certain southwestern regions. In South China and Jiangnan, early‑season densities were low, rose rapidly during the mid‑season, and then declined significantly thanks to timely control measures, leaving field numbers well below those of the previous year. In the middle and lower reaches of the Yangtze, the average density per 100 tillers remained below 300. By contrast, in the single‑cropping rice areas of the southwest, pest densities were higher, up 45%–50% year on year; in parts of southern Yunnan, northern Guizhou, southern Chongqing, and southern Sichuan, individual fields even exceeded 10,000 insects, with poorly managed plots showing signs of “overrun.”
　　The rice leafroller has generally been a relatively mild pest, but its incidence has been higher than last year. In the early‑rice growing areas of South China, it has occurred at moderate levels, with severe outbreaks in some localized early‑transplanted fields along the Guangxi coast. The cumulative affected area nationwide stands at 43.33 million mu, down 8.9% year on year. According to monitoring data from 304 rice‑pest surveillance stations under the National Pest and Disease Forecasting Network, the rice leafroller began migrating into China’s coastal regions of South China in late April; the peak migration period arrived about 10 days earlier than last year, with initial influxes smaller but later surges larger. As of July 5, the total migratory influx had increased by 2.2% year on year, yet remained 5.3% lower than the average for the same period over the past five years. Notably, the northern parts of Southwest China, the Jiangnan region, and the middle‑and‑lower reaches of the Yangtze River have seen markedly higher migration volumes compared with the previous year—e.g., Fujian, Hunan, and Jiangxi reported increases of 35%–60%, while Jiangsu, Chongqing, and Sichuan recorded 5–7 times the levels of the same period last year. Field larval populations are higher than last year, with leaf‑rolling damage slightly more severe than in 2022; leaf‑rolling rates generally remain below 5%, with isolated instances reaching 11%–24%.
　　The incidence of the rice stem borer was more severe than last year, with particularly heavy outbreaks in the rice-growing regions of southern Jiangnan. The cumulative affected area nationwide reached 87.8 million mu‑times, up 2.4% year on year. Post‑winter field populations remained high, 20%–30% greater than the same period last year; moth peaks arrived earlier and were accompanied by large moth counts. According to monitoring data from 304 rice‑crop sites under the National Pest and Disease Forecasting Network, as of July 5, total moth catches at light traps had increased by 34.2% compared with the same period last year, with Zhejiang and Hunan recording 2.5 and 2 times the levels of the previous year, respectively. Field egg densities were also high, resulting in significant damage: the rate of dead‑sheath plants generally ranged from 2% to 8%, with some areas reaching 11%–15%; the proportion of dead‑sheath clumps typically stood at 7%–14%, locally soaring to 30%–100% in parts of central and southern Hunan and southern Jiangxi.
　　Rice blast in the southern early‑rice region has been mild in the early stages and more severe later, with overall incidence remaining light but localized outbreaks becoming heavier. Nationwide, the cumulative affected area totaled 11.02 million mu, a 20.7% decrease year on year. In the early growth phase, leaf blast was generally less severe than last year, though some eastern Guangxi rice areas experienced relatively heavy infestations, with disease‑leaf rates reaching 15%–30% and, in isolated fields, symptoms of yellow dwarf and stunted tillering. In the later stage, panicle neck blast was more severe than last year, with typical diseased‑panicle rates ranging from 0.1% to 4%; in certain fields in the Jiangnan region, diseased‑panicle rates soared to 50%–75%.
　　Sheath blight was moderately severe to locally severe in the early rice-growing regions of South China and the Jiangnan area, but less so than in the previous year. The cumulative affected area nationwide reached 64.89 million mu, a 12.0% decrease compared with the same period last year. In the early stages, high temperatures and limited rainfall resulted in only mild incidence; however, starting in late May, increased rainfall triggered the peak epidemic phase, with rapid disease progression and heavy field damage. Disease‑infested tillers typically accounted for 13%–38%, with some fields reaching as high as 45%–75%.
　　In South China and the Jiangnan rice-growing regions, southern rice black-streaked dwarf disease has generally been mild but is showing a trend of resurgence. The incidence rate of infected tillers typically ranges from 1.1% to 2.4%, with some mid-season rice fields reaching as high as 20% to 30%. Nationwide, the cumulative affected area stands at 270,000 mu, a 25% decrease compared with the same period last year.
　　2 Forecast of the Occurrence Trends of Diseases and Pests in Mid- to Late-Season Rice
　　Rice pest outbreaks: Brown planthoppers are expected to occur at moderate to severe levels in the rice-growing regions of South China, the Yangtze River Basin, and eastern Southwest China, with localized outbreaks; the affected area is projected at 275 million mu‑times. Rice leafrollers are generally expected to occur at a moderate level, with more severe infestations in the lower Yangtze River region, affecting 170 million mu‑times. Two-brooded stem borers are forecast to be at a moderate level overall, with heavier outbreaks in the Yangtze River Basin and northern Southwest China, covering 135 million mu‑times. Three-brooded stem borers are expected to occur at a mild level in South China, affecting 9 million mu‑times. Other pests, including large stem borers, rice gall midges, rice stem flies, and armyworms, will also appear to some extent in certain rice‑growing areas, with a total affected area of 51 million mu‑times.
　　Rice diseases: Blast is expected to occur at a generally moderate level, with a risk of severe outbreaks in the northern parts of Southwest China, the middle and lower reaches of the Yangtze River, and the Northeast rice-growing region, affecting 66 million mu‑times. Sheath blight will be moderately severe across most rice-growing areas in southern China, with localized severe outbreaks, covering 185 million mu. Rice false smut is expected to be moderate overall, with localized severe outbreaks, in the central and eastern Jiangnan region, the northern parts of Southwest China, the middle and lower Yangtze River basin, the Jianghuai area, and the southern part of Northeast China, affecting 46 million mu‑times. Southern rice black-streaked dwarf disease is expected to be mild overall in southern rice-growing regions, though localized areas in South China and Jiangnan face a risk of severe outbreaks, affecting 4 million mu‑times. Other diseases, such as bacterial leaf blight, will occur to some extent in certain rice-growing areas, covering 29 million mu‑times.
　　3 Main Basis for the Forecast
　　Current pest and disease populations meet conditions for moderate-to-severe outbreaks. In South China, the Jiangnan region’s mid-season rice areas, and the Southwest’s single‑cropping rice zones, brown planthoppers are increasing rapidly, with high egg counts; the average number of insects per 100 tillers ranges from 600 to 1,400, and the average egg count per 100 tillers is 200 to 1,300. For stem borers, egg counts in South China, the Jiangnan region, and the Southwest rice areas are twice those of the same period last year, with larval densities typically between 1,600 and 3,500 per mu and egg densities averaging 10,000 to 20,000 per mu. In northern South China, northern Southwest China, and the Jiangnan rice regions, the overwintering population of the second‑generation stem borer remains relatively high, with larval densities generally ranging from 800 to 1,100 per mu. Rice blast is widespread across southern rice-growing areas, affecting numerous locations and a broad range of cultivars, while sheath blight tends to be severe year after year, with ample pathogen inoculum in the fields. As for southern rice black‑streaked dwarf disease, virus sources are fairly abundant in South China, the Southwest, and the Jiangnan rice regions; according to tests conducted by South China Agricultural University, multiple monitoring sites in these areas have whitebacked planthopper–borne virus rates of 2% to 5%, providing an effective source of infection for mid- to late‑season rice.
　　Cropping systems and rice varieties generally favor the occurrence of pests and diseases. In China’s South China and Jiangnan rice‑growing regions, the extensive intercropping of single‑ and double‑cropped rice creates favorable conditions for migratory rice pests and stem borers to move between fields and cause damage. In the middle and lower reaches of the Yangtze River, the uneven maturity of single‑crop rice provides an ample food supply for migratory pests, prolonging their period of harm; at the same time, it increases the likelihood that susceptible growth stages will coincide with prolonged rainy weather, thereby promoting the incidence of rice blast and false smut. Currently, mid‑ and late‑season rice varieties are predominantly characterized by high quality, high yield, robust culms with large panicles and densely packed grains. Under intensive cultivation practices involving high levels of water and fertilizer, these conditions readily give rise to localized microclimates of warm, humid environments, which facilitate the establishment and proliferation of rice pests and diseases. Moreover, although the disease resistance of the main cultivated varieties has improved compared with the previous two years, it remains relatively low, and some varieties have experienced a decline or loss of resistance, creating favorable circumstances for the widespread outbreak of diseases such as rice blast and false smut.
　　Meteorological conditions are generally favorable. According to forecasts from the National Climate Center, during this year’s peak summer months (July–August), temperatures across most of China are expected to be higher than average for this time of year. The main areas prone to heavy rainfall—eastern South China, southeastern Jiangnan, northern Southwest China, and Northeast China—will provide conducive conditions for the immigration and reproduction of migratory rice pests, as well as for the occurrence and spread of epidemic rice diseases. In addition, the number of typhoons making landfall in China during the summer and autumn seasons is projected to be 2–3 more than usual, with significant impacts on southern China and the southeastern coastal regions. This will favor the development of bacterial rice diseases in these areas and increase uncertainty regarding the emergence of “two‑migration” pests, potentially leading to localized, concentrated damage in certain rice‑growing regions.