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 in 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 Yangtze River Basin, and eastern Southwest China; stem borers will be moderately severe in the lower Yangtze River region; and two-brooded stem borers will be moderately severe in the Jiangnan and northern Southwest rice-growing areas, with a combined affected area of 640 million mu‑times. Meanwhile, sheath blight is anticipated to be moderately severe across most southern rice-growing areas, while blast 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-Stage Pest and Disease Occurrence in Early Rice and Single-Cropping Medium-Rice Fields
　　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 stem borer migration onset was earlier than last year but close to the long-term average; in the southwest and the middle Yangtze rice‑growing areas, it began 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 total stem borer arrivals were at their 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, arrival numbers were notably higher: for example, Hubei recorded an 88.6% year‑on‑year increase in total arrivals, and a 73.9% rise compared with the five‑year mean. Field populations remained generally low, though locally elevated in certain southwestern rice‑growing 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 levels well below those of the same period last year. In the middle and lower reaches of the Yangtze, the average number of insects per 100 tillers stayed 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 exceeded 10,000 insects, with poorly managed plots even showing “massive breakthroughs.”
　　The rice leafroller has generally been a relatively mild pest, though more severe than last year. In the early‑rice growing regions of South China, it has occurred at moderate levels, with localized outbreaks in some coastal areas of Guangxi where early transplanting took place. Nationwide, the cumulative affected area 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 southern coastal regions 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 number of migrants had increased by 2.2% compared with the same period last year, yet remained 5.3% lower than the five‑year average for this time of year. Notably, the northern parts of Southwest China, as well as the rice‑growing areas of Jiangnan and the middle and lower reaches of the Yangtze River, recorded significantly higher migration volumes year on year—e.g., Fujian, Hunan, and Jiangxi saw increases of 35%–60%, while Jiangsu, Chongqing, and Sichuan reported 5–7 times the levels of the previous year. Field larval populations exceeded those of the same period last year, with leaf‑rolling damage slightly heavier than in 2022; leaf‑rolling rates generally remained 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 central and southern Hunan and southern Jiangxi.
　　Rice blast in the early‑rice growing regions of southern China has been mild in the early stages but more severe later on, with overall incidence remaining light and localized outbreaks relatively heavy. Nationwide, the cumulative affected area totaled 11.02 million mu, a 20.7% year‑on‑year decrease. In the early growth phase, leaf blast was generally lighter than last year, though some eastern Guangxi areas experienced more serious outbreaks, with disease‑leaf rates reaching 15%–30% and, in isolated fields, symptoms of yellow dwarfing 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 Yangtze River Basin, but less so than 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 incidence ranged from 13% to 38%, with some fields showing rates as high as 45% to 75%.
　　In South China and the Jiangnan rice-growing regions, southern rice black-streaked dwarf disease has been generally 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 situation: Brown planthopper is expected to occur at a moderate-to-heavy level across rice-growing areas in South China, the Yangtze River Basin, and eastern Southwest China, with localized outbreaks; the affected area is projected at 275 million mu‑times. Rice leafroller is generally expected to occur at a moderate level, with heavier infestations in the lower Yangtze River region, affecting 170 million mu‑times. Two-brooded stem borer is 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 borer is expected to occur at a light level in South China, affecting 9 million mu‑times. Other pests, including large stem borer, rice gall midge, rice stem fly, and armyworm, are anticipated to occur to varying degrees 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 forecast 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 generally mild across southern rice-growing regions, though there is a risk of severe outbreaks in parts of South China and Jiangnan, 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 middle‑season rice areas of the Yangtze River region, and the single‑cropping rice zones of Southwest China, 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 number of eggs per 100 tillers is 200 to 1,300. For stem borers, egg counts in South China, the Yangtze River region, and the Southwest rice areas are twice those of the same period last year; larval densities typically range from 1,600 to 3,500 per mu, and egg densities generally reach 10,000 to 20,000 per mu. In northern South China, northern Southwest China, and the Yangtze River rice regions, the overwintering population of the second‑generation stem borer remains relatively high, with larval densities averaging 800 to 1,100 per mu. Rice blast is widespread across southern rice-growing areas, affecting numerous locations and a wide 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 Yangtze River rice regions; according to tests conducted by South China Agricultural University, at multiple monitoring sites in these regions, the positive rate among whitebacked planthoppers carrying the virus ranges from 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 while increasing the likelihood that susceptible growth stages will coincide with prolonged rainy weather—both factors promoting the incidence of rice blast and false smut. At present, 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 that are warm and humid, further facilitating the development and reproduction 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 at a relatively low level; in addition, some varieties have experienced a decline or loss of resistance, thereby creating favorable conditions 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 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.