Current Dynamics of Rice Diseases and Pests

Release Date:

2018-06-30

　　At present, early‑season rice in South China and the Jiangnan region is at the heading–grain‑filling to milky‑ripe stage, while mid‑season rice in Jiangnan, as well as single‑cropping rice in Southwest China, the middle and lower reaches of the Yangtze River, and Northeast China, are in the tillering stage. According to monitoring across regions, since early June, the number of “two‑migratory” pests trapped in light traps and their field populations have been lower than the same period last year in southern rice‑growing areas, though locally higher in parts of the middle Yangtze River; the stem borer has remained relatively abundant in mid‑season rice fields in Jiangnan. Recently, blast disease on the panicle neck has begun to appear in early‑season rice areas in the south, with severe outbreaks reported in some localized fields in Jiangnan. Nationwide, the cumulative area affected by rice diseases and pests has reached 197 million mu‑times, up 5% year on year. In the coming period, prevailing weather conditions are generally favorable for the development of diseases and pests in northern Jiangnan and the Jianghuai rice‑growing region. All localities should closely monitor field dynamics, promptly issue pest and disease advisories, and provide timely guidance to farmers on effective control measures.
　　I. Rice planthoppers
　　Brown planthoppers have occurred at moderate levels in the southern rice-growing regions, with a cumulative affected area of 44.73 million mu‑days, up 0.4% year on year. Since early June, monitoring in the South China and Southwest rice areas has detected trap peaks exceeding 1,000 insects per trap; in Tianyang, Guangxi, and Leizhou, Guangdong, single‑lamp, single‑day trap peaks surpassed 10,000 insects. However, overall insect counts under light traps remain markedly lower: according to data from 280 regional rice pest and disease monitoring stations nationwide, total trap catches from June 1 to 20 declined by 73.3% year on year, with only Hubei and Chongqing showing year‑on‑year increases of 52.1% and 16.9%, respectively. Field populations are generally below last year’s levels, except in Yunnan, Chongqing, and Hubei, where they are 7.8%, 47.5%, and 64.6% higher, respectively. In South China, the Jiangnan region, and the Southwest, the average number of insects per 100 rice tillers ranges from 150 to 900, with peak densities reaching 1,500 to 3,000. In the middle and lower reaches of the Yangtze River, the average is typically fewer than 50 insects per 100 tillers.
　　II. Rice Leafroller
　　The rice leafroller has been occurring at a relatively mild level in the southern rice-growing regions, with a cumulative affected area of 26.87 million mu‑times, up 36.4% year on year. In the first half of June, small moth‑attracting peaks were detected in South China and the southern part of the Yangtze River Basin; overall moth catches remained low. According to data from 280 regional monitoring stations nationwide, total moth captures from June 1 to 20 declined by 25.4% compared with the same period last year, with Sichuan being the sole exception, showing a 93.9% year‑on‑year increase. Field pest populations were also lower than last year: in South China and the Yangtze River Basin, adult densities generally ranged from 40 to 250 per mu, with localized peaks of 1,000 to 1,700 in central and northern Guangxi; larval densities averaged 1,000 to 5,000 per mu, with some areas reaching 10,000 to 20,000, all below the levels of the previous year—except in Hunan, where numbers rose by 22.8%. In the Southwest and the middle reaches of the Yangtze River, adult densities typically stayed below 20 per mu, while larval densities averaged 150 to 400 per mu; in Hubei, the average larval density was 161 per mu, markedly higher than the 4 per mu recorded at the same time last year, and in Chongqing, larval counts increased by 40% year on year. Field damage from leaf rolling was light, with leaf‑rolling rates generally below 3%; in Longnan, Jiangxi, isolated untreated plots showed rates as high as 8%.
　　III. Rice Stem Borer
　　The rice stem borer is expected to occur at moderate levels overall, with localized outbreaks of greater severity, across northern South China, the northern Southwest, the Jiangnan region, and the middle‑ and lower‑reaches of the Yangtze River. The cumulative affected area totals 65.4 million mu‑times, up 0.9% year on year. At present, in northern South China and the early‑rice areas of Jiangnan, larval densities generally range from 200 to 900 per mu, with higher counts reaching 1,000 to 2,000; in the mid‑season rice regions of Jiangnan and the single‑cropping rice areas of the northern Southwest, larval densities typically fall between 500 and 1,500 per mu, peaking at 3,000 to 4,000, with some fields in Hengyang, Hunan, exceeding 10,000 larvae per mu. Field damage is more severe than during the same period last year: in early‑rice areas of South China and Jiangnan, the dead‑heart rate generally stands at 0.3% to 3.3%, with localized plots in Shishou, Hubei, reaching as high as 55%; in the mid‑season rice regions of the northern Southwest and Jiangnan, the dead‑sheath rate ranges from 4% to 10%, with some fields in Wansheng, Chongqing, reporting rates as high as 22%.
　　IV. Sheath Blight
　　Sheath blight is occurring at moderate to severe levels in the early rice-growing regions of southern China, similar to the same period last year. The cumulative affected area stands at 51.14 million mu, up 5.3% year on year. At present, the incidence of infected plants in fields generally ranges from 5% to 35%, with some areas reaching 50% to 85%; the proportion of infected tillers typically falls between 13% and 43%, peaking at 60% to 100%.
　　V. Rice Blast Disease
　　Rice blast has been relatively mild in the South China, Southwest China, Jiangnan, and middle Yangtze River rice‑growing regions. The cumulative area affected by leaf blast totaled 5.58 million mu, a 19.3% year‑on‑year decrease; the cumulative area affected by panicle neck blast reached 470,000 mu, up 20.6% from the previous year. At present, leaf blast incidence generally ranges from 1% to 4%, with higher rates of 5% to 10%; in some poorly managed fields, it has soared to 40%–85%. In Changsha, Hunan, isolated fields have even experienced “root‑bound” leaf blast. Panicle neck blast is progressively manifesting in the rice‑growing areas of South China and Jiangnan, with disease‑affected panicle rates typically between 0.1% and 1.6%; in localized plots in Dongfang, Hainan; Xiajiang, Jiangxi; and You County, Hunan, these rates have climbed as high as 50%–60%, and in certain fields in You County, total crop failure has occurred.
　　VI. Future Trends and Recommendations
　　According to forecasts from the China Meteorological Administration, over the next 10 days, eastern Southwest China, northern Jiangnan, and the Jianghuai region will experience successive rounds of relatively heavy rainfall, while northern South China, most of Jiangnan, and southern Jianghuai will see high temperatures exceeding 35°C. These weather conditions will favor the northward migration of “two‑generation” migratory pests from the early rice‑growing areas of South China and Jiangnan into northern Jiangnan and the Jianghuai rice‑growing regions, where they may reproduce and cause damage; however, they will be unfavorable for the occurrence of diseases and pests in the early rice‑growing areas of South China and Jiangnan. All localities are urged to continue strengthening monitoring, comprehensively track pest and disease dynamics, issue timely and accurate pest‑and‑disease advisories, and effectively implement guidance on prevention and control measures.