National Agricultural Technology Center: Be on alert for localized outbreaks of “two-migration” pests in the late stage of early rice.

Release Date:

2019-06-17

At present, most early‑rice crops in southern China are in the panicle‑initiation stage, a critical period for the occurrence and damage caused by the “two‑migratory” rice pests. According to monitoring across various regions, since mid‑May, the early‑rice areas of South China, the Yangtze River Basin, and southwestern China have experienced substantial pest influxes and high field populations, with damage levels markedly higher than during the same period last year. As of June 12, the cumulative affected area for brown planthopper and stem borer has reached 35.25 million mu and 26.51 million mu, respectively—up 30.5% and 69.5% year on year. In the coming phase, widespread rainfall is expected across much of the middle and lower reaches of the Yangtze River and areas further south, with precipitation likely to exceed normal levels, creating favorable conditions for the reproduction and proliferation of these “two‑migratory” pests. Forecast…

At present, most early‑rice crops in southern China are in the panicle‑formation stage, a critical period for the occurrence and damage caused by the “two‑migratory” rice pests. According to monitoring across various regions, since mid‑May, the early‑rice areas of South China, the Yangtze River Basin, and southwestern China have experienced substantial pest influxes and high field populations, with damage levels markedly higher than during the same period last year. As of June 12, the cumulative affected area for brown planthopper and stem borer has reached 35.25 million mu and 26.51 million mu, respectively—up 30.5% and 69.5% year on year. In the coming phase, widespread rainfall is expected across much of the middle and lower reaches of the Yangtze River and areas further south, with above‑average precipitation, creating favorable conditions for the reproduction and proliferation of these two‑migratory pests. It is forecast that, in the later growth stage of early rice, brown planthopper will occur at moderate to severe levels (level 4) in South China and eastern parts of the Yangtze River Basin, with localized outbreaks (level 5) in eastern South China and eastern Yangtze River Basin; stem borer will be at moderate levels (level 5) across South China and the Yangtze River Basin, with localized outbreaks (level 4) in northern South China and southern Yangtze River Basin.

1. Large influx under the lamp

Since mid-May, rice planthoppers have been migrating in large numbers into the rice-growing regions of South China, the Yangtze River Basin, and the southern part of Southwest China. Notably, from May 16 to 19 and from May 25 to 28, the northern parts of South China and the southern Yangtze River Basin experienced sudden spikes, with individual light traps recording over a thousand insects per day. From May 31 to June 3, eastern South China saw consecutive days of migration peaks exceeding one thousand insects per trap per day, and on June 7, Jiangcheng County in Yunnan Province recorded a peak of 112,000 insects caught by a single trap in a single day. According to monitoring data from 271 regional stations nationwide, since mid-May, the total influx of rice planthoppers has been 1.9 times that of the same period last year, with brown planthopper arrivals 2.1 times higher than last year. By province, Fujian’s planthopper influx was 14 times that of the previous year, while Guangxi, Hainan, and Jiangxi reported 2–3 times the levels of the prior year; Hunan saw a year-on-year increase of 72.6%.

Since late May, the rice leafroller has continued to migrate into the rice-growing regions of South China and the Yangtze River Basin, with the main influx concentrated in northern South China and southern Jiangnan. The pest has also spread to northern Jiangnan and the middle reaches of the Yangtze River, with the peak migration occurring about 10 days earlier than last year. According to monitoring data from 271 regional stations nationwide, the total number of adult rice leafrollers trapped at light traps is 2.2 times that of the same period last year. Notably, in Zhaoping, Guangxi, a single trap recorded more than 100 moths per day for 10 consecutive days between May 21 and 30, with a peak of 1,920 moths on May 22. Additional peak migration events—exceeding 200 moths per trap per day—were observed in Shanglin and Liujiang in Guangxi, Xiangzhou, Dao County in Hunan, and De’an in Jiangxi.

2 High pest population density in the field

At present, in the early‑rice monitoring areas of South China, the Yangtze River Basin, and the southern Southwest, the rice planthopper population averages 350–1,300 insects per 100 hills, with peak densities reaching 2,000–3,000; in Gaoming, Guangdong, the highest recorded count was as high as 36,000. In nationwide field surveys, the weighted average population is 200–850 insects per 100 hills, with higher counts ranging from 1,000 to 3,000; in Gaoming, Guangdong, and Lancang, Yunnan, the figures reached 15,000 and 12,000, respectively. Compared with the same period last year, pest populations in the rice-growing regions of South China and the Yangtze River Basin are markedly elevated: for example, Fujian’s average density is 679 insects per 100 hills, five times that of the previous year; in Jiangxi, the density is 5.2 times the level of the same period last year, with An Yuan recording a peak of 8,900 insects per 100 hills.

In the rice-growing regions of South China and the Yangtze River Basin, the average number of adult moths per mu typically ranges from 100 to 700, with peak densities reaching 900 to 2,000. In parts of southeastern Guangxi, central Guangxi, and southern Jiangxi, local peaks can soar to 3,000–6,000 moths per mu, while in Huaiji and Qingyuan in Guangdong, maximum counts have exceeded 10,000 moths per mu. Compared with the same period last year, the average moth density across these regions has increased 2.8-fold. Specifically, Fujian’s average stands at 176 moths per mu—15 times the level of the previous year; Jiangxi reports 220–700 moths per mu, 3.8 times last year’s figure; and Hunan’s daily average has risen to 1.4 times last year’s level and 1.9 times the long-term average for this time of year. At present, egg populations remain high in these areas, with larval densities generally ranging from 2,000 to 8,000 per mu, and in some cases reaching 10,000–32,000. In southeastern and central Guangxi, localized fields report 45,000–60,000 larvae per mu. Egg counts are typically 2,500–7,000 per mu, with peaks of 10,000–50,000; in Huaihua, Hunan, the average is 8,246 eggs per mu, up 73.3% year on year, while in Lianhua, Taihe, Yudu, Huichang, and other locations in Jiangxi, egg counts have reached as high as 8,000–56,000 per mu.

3 Favorable climatic conditions

According to forecasts from the China Meteorological Administration, over the next 10 days, cumulative rainfall in South China, the Jiangnan region, the Jianghan Plain, and eastern parts of Southwest China is expected to range from 50 to 80 millimeters, with some areas receiving 100 to 180 millimeters and localized spots exceeding 200 millimeters. These totals are 30% to 60% above normal for this time of year, with some locales seeing more than double the usual amount. For the subsequent 11 to 20 days, cumulative rainfall across much of the middle and lower reaches of the Yangtze River and areas further south is projected to be 50 to 100 millimeters, with parts of Jiangnan and northern South China experiencing 120 to 200 millimeters, and isolated areas surpassing 250 millimeters. Overall, these accumulations are 20% to 50% above normal for this period, with some locations seeing more than double the typical levels. The frequent and heavy precipitation will facilitate the migration, settlement, and reproduction of “two‑generation” pest species, while simultaneously posing challenges to control efforts.

Recently, the influx of “two‑migration” pests has been substantial, with high pest densities in fields. Rice is currently in the booting stage, benefiting from ample nutrients, and upcoming weather conditions are favorable for the reproduction and proliferation of these pests. Consequently, there is a risk of localized outbreaks of “two‑migration” pests during the late growth period of early rice in parts of South China and the Jiangnan rice‑growing region. All localities are urged to attach great importance to this issue, strengthen monitoring, closely track the dynamics of “two‑migration” pest occurrences, promptly and accurately disseminate pest‑and‑disease advisories, and effectively implement guidance on prevention and control measures.

Source: National Agricultural Technology Extension Service Center

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