It is forecast that in 2019, brown planthoppers, stem borers, and sheath blight will occur at a relatively severe level in early-season rice.

Release Date:

2019-05-15

On May 10–11, the National Agricultural Technology Extension Center convened a national consultation meeting on the forecast of major early rice diseases and pests in Hangzhou, Zhejiang, bringing together pest‑monitoring and forecasting technicians from the main rice‑producing provinces in southern China, as well as relevant experts from research and educational institutions. Based on a comprehensive analysis of current pest and disease populations, resistance to pesticides, rice cultivation practices, and prevailing climatic conditions, the participating experts projected that this year’s early rice diseases and pests will generally range from moderate to severe (levels 3–4), exceeding last year’s levels. Specifically, brown planthopper, stem borer, and sheath blight are expected to occur at a severe level (level 4); rice leafroller at a moderate level (level 3); and rice blast at a relatively mild level (level 2). The total affected area nationwide is estimated at 250 million mu‑times.

On May 10–11, the National Agricultural Technology Extension Center convened a national consultation meeting on the forecast of major early rice diseases and pests in Hangzhou, Zhejiang, bringing together pest‑monitoring and forecasting technicians from the main rice‑producing provinces in southern China, along with relevant experts from research and educational institutions. Based on a comprehensive analysis of current pest and disease populations, resistance to pesticides, rice cultivation practices, and prevailing climatic conditions, the experts predicted that this year’s early rice diseases and pests will generally range from moderate to severe (levels 3–4), exceeding last year’s levels. Specifically, brown planthopper, stem borer, and sheath blight are expected to be severe (level 4), while rice leafroller is projected to be moderate (level 3), and rice blast relatively mild (level 2). The total affected area nationwide is estimated at 250 million mu‑times, with pest infestations accounting for 170 million mu‑times and disease outbreaks for 80 million mu‑times.

I. Occurrence Trend

Brown planthopper infestations are expected to be severe (level 4), more intense than last year, affecting 62.0 million mu‑times; the area requiring control measures is 47.3 million mu‑times, accounting for 76.3% of the total affected area. Overall, infestations are heavier in the west and lighter in the east. Specifically, the whitebacked planthopper is projected to be severe (level 4) in South China, southern Jiangnan, and southwestern China; moderate (level 3) in the Jiangnan rice‑growing region; and mild (level 2) in the middle reaches of the Yangtze River. The brown planthopper is expected to be severe (level 4) in western South China; moderate (level 3) in southwestern China, western Jiangnan, and the middle reaches of the Yangtze River; and light to mildly severe (levels 1–2) in eastern South China, eastern Jiangnan, and the middle and lower Yangtze River rice‑growing regions.

The rice leafroller is at a moderate level of occurrence (Level 3), unchanged from the previous year, with an affected area of 43 million mu‑times. The area requiring control measures totals 28.5 million mu‑times, accounting for 66.3% of the total affected area. Specifically, in the South China and Jiangnan rice-growing regions, the pest is at a moderate level (Level 3); in eastern and northern Guangxi and western Guangdong, it is moderately severe (Level 4); and in Hainan, it is relatively mild (Level 2). In the southern Southwest and the middle–lower reaches of the Yangtze River, the pest is relatively mild (Level 2), while in southeastern Hubei, localized areas experience moderately severe infestations (Level 4).

The rice stem borer is expected to occur at a severe level (Level 4), exceeding last year’s incidence, with an affected area of 46 million mu‑times. The area requiring control measures totals 37.8 million mu‑times, accounting for 82.2% of the total affected area. Specifically, in the Jiangnan and middle–lower reaches of the Yangtze River rice-growing regions, the first generation is projected to be severely prevalent (Level 4); around Poyang Lake and in southeastern Hunan, it is expected to be highly prevalent (Level 5); and the second generation will be moderately prevalent (Level 3). In the South China rice-growing region, a clear upward trend is evident: northern South China will see moderate prevalence (Level 3), while southern South China will experience light to slightly light prevalence (Levels 1–2). In the southwestern southern rice-growing region, prevalence is expected to be slight (Level 2).

The rice stem borer is occurring at a mild level (Level 2) and showing a declining trend, with an affected area of 5.5 million mu. The area requiring control measures totals 720,000 mu‑times, accounting for 13.1% of the total affected area. The primary outbreak regions are the rice-growing areas of South China and southern Southwest China, while other rice-growing regions are experiencing mild infestations (Level 1).

Sheath blight occurred at a severe level (Level 4), more severely than the previous year, affecting 60 million mu of rice fields. The area requiring preventive measures totaled 90 million mu, 1.5 times the affected area. Specifically, most of South China, the Jiangnan region, and the middle and lower reaches of the Yangtze River experienced severe outbreaks (Level 4), with localized direct-seeded rice fields suffering extremely severe infestations (Level 5); in contrast, the southern part of Southwest China saw only mild outbreaks (Level 2).

Rice blast occurred at a relatively mild level (Grade 2), unchanged from the previous year, affecting 11.0 million mu‑times. The area requiring preventive measures totaled 27.5 million mu‑times, 2.5 times the affected area. Specifically, in the Jiangnan and southern Southwest rice-growing regions, the incidence was moderate (Grade 3); in the South China region, it was mild (Grade 2); and in older epidemic areas and fields planted with susceptible varieties, localized outbreaks were moderately severe (Grade 4).

Rice viral diseases occurred at a relatively mild level (Level 2), affecting 1 million mu‑times, or 1.4% of the early rice acreage. Among these, southern rice black-streaked dwarf disease poses a moderate to severe epidemic risk in certain rice-growing areas of South China and the Jiangnan region.

Other pests and diseases, including the rice stem borer, rice stem fly, rice false smut, bacterial leaf blight, and citrus leaf disease, have occurred to varying degrees in certain rice-growing areas, affecting a total area of 21.5 million mu‑times.

II. Basis for Forecasting

(1) Most pests and diseases have a baseline incidence level of moderate or higher.

Brown planthoppers began migrating into China in large numbers from late March, with the peak migration occurring 20 days earlier than last year. The influx of pests is markedly higher than usual: in Guangxi, the number of migrating insects in March–April was 31 times and 15 times that of the previous year and the long-term average, respectively, while in Hunan the infestation level approached that of the severe outbreak in 2007. At present, pest populations in the fields are higher than at the same time last year; in the southern rice-growing areas of South China, the average density is typically 300–800 insects per 100 tillers, with some plots reaching 1,000–2,500. In eastern Guangxi’s Mengshan County, densities have soared as high as 15,000–20,000 insects per 100 tillers, establishing a pest‑source base sufficient to support a moderately severe or worse outbreak.

The rice leafroller began migrating into the southern and central rice-growing regions of China in early April. Currently, both adult moth populations and larval densities are higher than at the same time last year. In the southern rice areas, adult counts typically range from 100 to 500 per mu, with localized fields in western Guangdong and southern Guangxi reaching as high as 1,200 to 6,800 adults per mu. Larval densities generally stand at 100 to 650 per mu, with some areas reporting 1,000 to 3,700 larvae per mu; in certain severely affected fields in Yangchun, Guangdong, larval counts have soared to 52,000 per mu, indicating a pest population base sufficient to support moderate-to-severe outbreaks.

The rice stem borer exhibits a relatively high overwintering population in the Jiangnan region and the middle‑ and lower‑reaches of the Yangtze River. In Hunan and Jiangxi, the average number of surviving larvae per mu ranges from 5,000 to 6,500, while in Fujian, Zhejiang, and Hubei it is between 2,000 and 2,700. Since mid‑April, overwintering adults have been emerging and laying eggs, migrating northward from southern areas. According to surveys across various localities, moth catches at light traps have exceeded both last year’s levels and the long‑term average—Hunan’s catch is 2.4 times that of the same period in a typical year, and Jiangxi’s is 1.1 times that of the previous year. Field egg counts are also elevated, with average numbers of egg masses per mu standing at 106 in Hunan and 291 in Jiangxi; in Hengnan and Liling in Hunan, egg masses have surpassed 900, indicating an overwintering population capable of supporting a severe or worse outbreak.

Sheath blight recurs severely year after year, with a large reservoir of pathogen in the fields, providing a substantial base for moderate to severe outbreaks. Rice blast occurs annually across numerous locations and on a wide scale, also maintaining a certain level of pathogen inoculum that supports epidemic potential.

(II) Rice cultivation practices and the increasing resistance of pests and diseases to pesticides are conducive to the occurrence of these pests and diseases.

In recent years, adjustments and optimizations in the structure of the cropping industry have led to a year-on-year decline in the acreage devoted to early rice, which has facilitated the concentrated occurrence and damage caused by migratory pests such as the brown planthopper and the stem borer. The predominant early‑rice varieties are high‑quality, high‑yielding but exhibit relatively weak resistance, posing a significant risk of disease outbreaks. Moreover, farmers tend to overapply nitrogen fertilizers, resulting in vigorous plant growth and dense canopy cover, thereby creating microclimatic conditions of moderate temperatures and high humidity that favor the emergence and spread of rice diseases and pests.

According to monitoring, the resistance of the rice stem borer to commonly used insecticides such as chlorantraniliprole and abamectin has increased to varying degrees. Specifically, in the eastern coastal areas of Zhejiang, the region surrounding Poyang Lake in Jiangxi, and southern Hunan, populations of the rice stem borer have developed high levels of resistance to chlorantraniliprole; meanwhile, populations in Zhejiang and Hunan have attained high resistance to abamectin. These developments are likely to exacerbate the incidence and damage caused by the rice stem borer.

(3) Climatic conditions are conducive to the outbreak and spread of pests and diseases.

According to forecasts from the National Climate Center, most of South China and southern Jiangnan are expected to experience above-normal precipitation during May, while northern Jiangnan and the middle and lower reaches of the Yangtze River will see above‑normal rainfall from June to August. These periods are likely to feature frequent, intense precipitation events, which will favor the northward migration and reproduction of “two‑migration” pests as well as the occurrence and spread of plant diseases. In addition, this year’s typhoon season is projected to bring a number of landfalls close to or slightly above normal, with stronger-than-average intensity and an earlier first landfall. During the peak activity period, typhoons are expected to track mainly westward and northwestward, primarily affecting South China, Jiangnan, and the southeastern coastal regions. Consequently, “two‑migration” pests may concentrate in certain areas and cause significant damage, while bacterial diseases could also re‑emerge and spread locally.

Source: Pest and Disease Forecasting Division

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