Post‑autumn dynamics of major rice diseases and pests and their forecast for the next stage

Since the onset of autumn, as the intense heat has subsided across most of southern China, major rice pests and diseases have continued to spread in the mid- and late‑season rice-growing regions, with particularly severe damage in some localized fields. As of September 2, the nationwide area affected by rice pests and diseases totaled 596 million mu‑times, a decrease of 18.6% compared with the same period last year. Based on a comprehensive analysis of current pest and disease incidence, host‑plant conditions, and anticipated weather patterns, it is projected that the peak period of damage from major rice pests and diseases will persist through the end of September. In the South China rice region, there is a high risk of locust‑type planthoppers erupting into full‑scale outbreaks, while in the Jiangnan rice region, borer moths pose a significant threat. Additionally, areas impacted by typhoons face an elevated risk of widespread dissemination and epidemic outbreaks of bacterial diseases in rice.

I. Current Status of Major Pest and Disease Outbreaks

(1) Brown planthopper. As of early September, the cumulative area affected nationwide totaled 153 million mu‑times, down 24.5% from the same period last year, with overall infestation levels remaining relatively mild. Light trap catches showed a general decline across southern rice-growing regions from August 24 to 30, with most areas recording month-on-month reductions of 10%–80%; however, at four monitoring sites in northeastern Guangxi, central Fujian, and western Jiangxi, the weekly cumulative catch per light exceeded 1,000 individuals. Specifically, on August 24 in Lingchuan, Guangxi, and August 25 in Datian, Fujian, single‑light catches reached 5,600 (97.0% brown planthopper) and 3,200 (98.5% whitebacked planthopper), respectively. Field counts of insects per 100 tillers averaged 970 in Hainan and 700 in Guizhou, up 2.8‑fold and 3.5‑fold year on year, respectively; in most of South China, southern Southwest China, the Jiangnan region, and the Jianghan Plain, typical counts ranged from 220 to 580; elsewhere, they generally stood at 60–120. Notably, in certain fields in Tengchong, Yunnan; Ziyuan and Xing’an, Guangxi; Leishan and Bozhou, Guizhou; Jiangmen, Guangdong; Shunchang, Fujian; Shaoyang and Dongkou, Hunan; Xianfeng, Hubei; and Yongkang and Chun’an, Zhejiang, field counts exceeded 3,000 per 100 tillers, with some plots reaching 20,000–30,000, and even instances of “piercing‑through” damage.

(2) Rice leafroller. As of early September, the cumulative area affected by rice leafroller nationwide totaled 110 million mu‑times, a 30.0% decrease compared with the same period last year, indicating an overall lighter-than-usual outbreak. In terms of moth catches, monitoring stations across the country recorded a cumulative total of 108,000 moths in August, down 60.0% from the same period last year and 23.7% below the five-year average. Since August 24, moth peaks have been observed at 15 monitoring sites along the middle and lower reaches of the Yangtze River and around Lake Taihu; among these, Yuanjiang in Hunan, Chongming in Shanghai, and Tongzhou in Jiangsu each reported weekly moth counts of 1,400–2,500 per trap. The average larval density per mu ranged from 1,400 to 4,200 in central and western South China, the Jiangnan region, and the lower Yangtze rice‑growing areas, while other regions recorded 140–800 larvae per mu. In localized fields in Yuanjiang and Linli in Hunan, Qinnan in Guangxi, Longmen in Guangdong, and Fuyang in Zhejiang, densities reached 30,000–35,000 larvae per mu, with individual plots in Luchuan, Guangxi, even exceeding 84,000 larvae per mu.

(3) Chilo suppressalis. As of early September, the cumulative area affected by this pest nationwide totaled 140 million mu‑times, a 4.9% decrease compared with the same period last year, though overall conditions remained relatively severe. In most rice-growing regions of southern China, the second generation is nearing its end, while the third generation is just beginning to peak. During August, monitoring stations across the country recorded a cumulative total of 238,000 moths, up 37.0% from the same period last year and 85.3% above the five-year average. Since August 24, several monitoring sites in Hubei and Hunan have reported moth peaks: on August 24, Zhijiang, Hubei, recorded 4,637 moths at a single trap; on August 29, Shaodong, Hunan, logged 1,056 moths. Additionally, from August 24 to 26 in Xinning, Hunan, and from August 24 to 27 in Dongkou, as well as from August 26 to 29 in Huitong, daily averages per trap reached 5,621, 3,708, and 5,544 moths, respectively—each exceeding levels seen during the same period last year. The average larval density per mu stood at 2,600 in Jiangxi and 1,900 in Hunan, both surpassing the threshold for severe infestation, though down 5.0% and 5.9%, respectively, year on year. Zhejiang reported 850 larvae per mu, up 6.3% year on year. In the middle and lower reaches of the Yangtze River, as well as central and western Jianghuai, typical densities ranged from 310 to 410 larvae per mu, an increase of 37.5% to 75.0% compared with the previous year. Notably, in Wenling, Zhejiang; Liuyang, Hunan; and Anfu, Jiangxi, average densities reached 12,000 to 25,000 larvae per mu, with some severely affected plots exceeding 60,000 larvae.

(4) Rice blast. As of early September, the cumulative area affected by rice blast nationwide totaled 20.17 million mu, a 23.8% decrease compared with the same period last year, indicating generally mild incidence. At present, in the Southwest and Northeast rice-growing regions, single-cropping rice has gradually entered the maturity stage, and the disease situation in the fields is essentially settled. In the Jiangnan, middle and lower reaches of the Yangtze River, and the Jianghuai rice-growing areas, sustained drought has slowed the spread of the disease; average rates of infected leaves remain below 5%, and average rates of infected panicles are under 2%.

II. Analysis of Factors Influencing the Occurrence of Pests and Diseases in the Next Phase

Recently, double-cropping late rice in South China, the Jiangnan region, the middle and lower reaches of the Yangtze River, and the Jianghuai rice-growing area is at the tillering to booting stage, while mid-season rice in eastern South China, Jiangnan, the middle and lower Yangtze River, and most of the Jianghuai rice-growing area is in the grain-filling to maturity stage. Host growth stages and prevailing nutritional conditions remain conducive to the occurrence and damage caused by pests and diseases.

Since the onset of autumn, high-temperature and drought conditions have markedly abated across most of southern China, and the adverse impacts of earlier meteorological disasters on rice production and the incidence of pests and diseases have been alleviated to varying degrees. According to forecasts from the National Climate Center, in September, temperatures in southern rice-growing regions are expected to be near or above normal for this time of year, while precipitation is likely to be below average in the Jiangnan and middle‑and‑lower Yangtze River rice‑growing areas. Specifically, in parts of Jiangsu, Anhui, Shanghai, central and western Zhejiang, most of Jiangxi, southern Henan, much of Hubei, Hunan, northwestern Fujian, northern Guangxi, and eastern Guizhou, rainfall is projected to be 20%–50% lower than usual—conditions that are unfavorable for the reproduction and damage caused by “two‑migration” rice pests and for the spread of epidemic diseases, with no adverse effects on borers. In contrast, precipitation in the South China rice‑growing region is expected to be near normal, which is more conducive to the occurrence of these “two‑migration” pests. Additionally, during September, one to two tropical cyclones are likely to make landfall or affect China’s coastal areas, a frequency close to the long-term average; moreover, recent impacts from Typhoon Hinnamnor have brought sustained rainfall, localized heavy downpours, and strong winds to eastern coastal regions, creating conditions favorable for the dissemination and outbreak of bacterial diseases such as bacterial leaf blight in rice.

Source: Agricultural Inputs Herald