Forecast of the Occurrence Trends of Diseases and Pests in Mid- to Late-Season Rice

Recently, the National Agricultural Technology Center convened a meeting in Harbin, Heilongjiang Province. 2021 National Conference on the Forecast of Disease and Pest Outbreaks in Mid- and Late‑Season Rice, Based on a comprehensive analysis of the current pest and disease baseline, cultivation conditions, and climatic factors, technical personnel from plant protection agencies in 20 provinces (autonomous regions, and municipalities directly under the central government) that are major rice-producing areas, along with relevant experts, … It is projected that in 2021, major rice diseases and pests will occur at a generally severe level, affecting a total area of 920 million mu‑times, with pest infestations covering 630 million mu‑times and disease outbreaks spanning 290 million mu‑times. Specifically, brown planthopper and sheath blight are expected to be severe; stem borer, two-brooded stem borer, and blast will occur at moderate to severe levels; false smut will be moderate; and southern rice black-streaked dwarf disease is anticipated to be mild.

Brown planthopper infestations were severe, with a nationwide affected area of 270 million mu‑times. Specifically, the whitebacked planthopper was severely prevalent in eastern Southwest China and the Jianghan Plain, while it occurred at moderate levels across most of the Southwest, the middle and lower reaches of the Yangtze River, South China, the Jiangnan region, and the Jianghuai rice-growing areas. The brown planthopper was severely prevalent in eastern South China, most of the Southwest, the Jiangnan region, and the middle and lower reaches of the Yangtze River, and occurred at moderate levels across much of South China, eastern Southwest China, and the Jianghuai rice-growing areas.

The rice leafroller is expected to occur at a severe level in the western Jiangnan region and along the rivers and lakes of the middle and lower Yangtze River basin, while moderate infestations are anticipated across most of Jiangnan, the middle and lower Yangtze River basin, eastern Southwest China, and much of South China; the nationwide affected area is projected to reach 160 million mu.

The rice stem borer is severely prevalent in the western part of the Jiangnan region, while it occurs at moderate levels in the northwestern and southwestern regions, eastern South China, eastern Jiangnan, the middle and lower reaches of the Yangtze River, the Jianghuai area, and the central and southern parts of Northeast China. The total affected area nationwide amounts to 130 million mu‑times.

Other pests, including the gray planthopper, stem borer, large stem borer, rice stem fly, armyworm, and Taiwan rice stem borer, have occurred to varying degrees in certain rice-growing areas; the nationwide affected area totaled 69 million mu‑times.

Sheath blight has occurred at a severe level across most of South China, eastern Southwest China, the Jiangnan region, and the middle and lower reaches of the Yangtze River rice-growing areas, while it has been observed at a moderate level in eastern South China, most of Southwest China, and much of Northeast China. The total affected area nationwide amounts to 180 million mu‑times.

Rice blast poses a high risk of severe outbreaks in the hilly and mountainous regions of Southwest China and the Jiangnan area, as well as in the Northeast rice-growing region, while moderate outbreaks are expected in most other rice-growing areas; the nationwide affected area is estimated at 56 million mu.

Rice false smut is generally occurring at a moderate level, with a heightened risk of severe outbreaks during the heading and flowering stages if prolonged rainy weather persists; the nationwide affected area totals 38 million mu.

Overall, southern rice black-streaked dwarf disease has been relatively mild; however, it has occurred at moderate levels in parts of western Guangxi, southwestern Guangdong, and central-southern Hunan, affecting an area of 1 million mu.

Other diseases, including bacterial leaf blight, panicle rot, sesame leaf spot, and root-knot nematode disease, have occurred to varying degrees in certain rice-growing regions, with a total affected area of 15 million mu nationwide.

(1) The baseline populations of “two‑migration” pests and other diseases and pests meet the conditions for medium‑to‑high incidence.

At present, in most rice-growing areas of South China, the Jiangnan region, and Southwest China, the rice planthopper population averages 300–1100 insects per 100 plants; in eastern Southwest China and central Jiangnan, local peaks reach 60,000–100,000 insects per 100 plants. In the middle and lower reaches of the Yangtze River and the Jianghuai rice region, the average is 100–300 insects per 100 plants, with localized peaks as high as 4,000 in Shanghai. For the rice leafroller, field larval densities remain low: 5,000 in Hunan, 2,700 in Guangxi, and 1,200 in Chongqing; in other rice‑growing areas, numbers generally stay below 500, though in parts of west-central Hunan and central Guizhou, some fields exceed 100,000 larvae per 100 plants. As for the rice stem borer, larval densities in northern Southwest China, eastern South China, and the middle and lower Yangtze River rice region typically range from 250 to 450 per mu; however, in Hunan the average climbs to 3,500, surpassing the threshold for a severe outbreak (1,000). Rice blast continues to occur widely across many locations, with susceptible varieties still accounting for a notable share of plantings. Sheath blight remains a persistent problem, with ample pathogen inoculum available in the fields.

(2) Host crops and field ecological conditions are conducive to the occurrence of pests and diseases.

In China’s South China and Jiangnan rice-growing regions, the extensive co‑cultivation of single‑ and double‑cropped rice creates favorable conditions for the translocation and successive damage caused by migratory rice pests and stem borers. In the Southwest and the middle–lower reaches of the Yangtze River, the uneven maturity of single‑crop rice increases the likelihood that susceptible growth stages coincide with prolonged cloudy and rainy weather, thereby promoting the outbreak of climate‑dependent diseases such as blast and false smut. Across these areas, mid‑ to late‑season rice varieties are predominantly high‑quality; however, the resistance levels of the main cultivars remain relatively low, with some varieties experiencing a decline or loss of resistance. Moreover, under intensive cultivation practices characterized by high water and fertilizer inputs, the resulting favorable host nutrition and dense canopy further facilitate the occurrence and spread of rice diseases and pests.

(3) Overall meteorological conditions are favorable for the occurrence of epidemic diseases. and the northward migration of “two‑migration” pests

According to forecasts from the National Meteorological Center, during this year’s peak summer months (July–August), temperatures across China are expected to be generally above normal. Increased rainfall is anticipated in Northeast China, eastern Jianghuai, northeastern Jiangnan, the eastern and northern parts of Southwest China, most of the Jianghan region, and southern South China, creating favorable conditions for the outbreak and spread of rice diseases such as blast, sheath blight, and false smut, which could lead to localized, sudden epidemics. In contrast, southern Southwest China, South China, Jiangnan, and much of the middle and lower reaches of the Yangtze River are likely to experience below-normal precipitation. Meanwhile, areas including Jianghuai, Jianghan, and Jiangnan are expected to see a higher-than-normal number of days with high temperatures (daily maximum ≥35°C), resulting in intermittent heatwaves. These conditions will exert some suppressive effects on the population dynamics of “two‑migration” pests. However, 6–8 typhoons are forecast to make landfall in or significantly affect China in the second half of the year—close to the long-term average or slightly above it—potentially including northward‑moving systems that could markedly impact East China and regions further north, thereby facilitating the northward migration and subsequent damage caused by these pests.