Forecast of the occurrence trend of the third generation of armyworms

According to monitoring by the National Crop Pest and Disease Forecasting Network, since late July, most of Northeast China, North China, and Northwest China have experienced peak emergence of second-generation armyworm adults, with particularly high moth catches in some areas. Taking August’s meteorological conditions into account, it is projected that this year’s third generation of armyworms will generally occur at a lighter-than‑average level, affecting approximately 25 million mu of farmland. In regions where moth populations are high, weed cover is abundant, and climatic conditions are favorable, localized outbreaks of severe, high‑density damage are expected. The peak period for larval occurrence is anticipated to be from early to mid‑August.
The second generation of armyworms has a large area of occurrence.
Local pest populations are high in the northwest and southwest.
This year, the second-generation armyworm has been observed across 35 million mu nationwide, a 15% increase compared to 2020. Overall, infestations were moderate, with severe outbreaks in localized areas of Northwest and Southwest China—more intense than both last year and the long-term average. Nationwide, fields with 10–30 larvae per 100 plants accounted for 10 million mu, while areas experiencing more than 30 larvae per 100 plants covered 2.5 million mu. In specific regions—including central and northern Ningxia, western Inner Mongolia, central Shanxi, northern Shaanxi, central Gansu, and southern Yunnan—high-density, concentrated damage was recorded, with larval counts exceeding 500 per 100 plants, peaking at 2,000. Local authorities promptly organized control measures, resulting in a cumulative treated area of 40 million mu. With the exception of Ningxia and Inner Mongolia, where residual densities reached 3–5 larvae per square meter, most areas remained below 1 larva per square meter.
Adult moths of the second generation are at low levels in most areas.
Local moth populations are high in Northwest and North China.
Since July, adult second-generation moths have been reported successively across North China and Northeast China. In July, the cumulative moth counts at most monitoring sites remained below 100, significantly lower than both last year and the long-term average for the same period. Specifically, Feicheng and Zhangqiu in Shandong recorded 39 and 31 moths, respectively; across Shanxi Province, the average at all monitoring sites was 36, with Xiyi, Fenyang, and Yongji reporting 66 to 89 moths; in Hebei, the provincial average stood at 87, down from 214 in 2020 and 283 in 2019; in Jilin, Lishu, Changling, and Shuangliao reported 12 to 50 moths; and in Heilongjiang, most sites recorded 2 to 33 moths.
In some parts of northern China, moth populations remain relatively high, with individual high-altitude lamps, monitoring lamps, or sex pheromone traps recording cumulative catches exceeding 100 moths in July. Specifically, at high-altitude lamps: Pucheng, Huayin, and Fugu in Shaanxi recorded 5,000, 987, and 880 moths, respectively; Yanqing in Beijing logged 1,018; Laizhou in Shandong reported 287; Shuangcheng in Heilongjiang registered 264; and Pingluo in Ningxia recorded 253. At monitoring lamps: Pucheng and Fugu in Shaanxi reported 518 and 362 moths, respectively; Dameng in Hebei recorded 303; Urad Front Banner, Left Rear Banner, and Tongliao in Inner Mongolia reported 240, 113, and 110 moths, respectively; Shuangcheng, Ning’an, and Jixian in Heilongjiang recorded 201, 175, and 166 moths, respectively; Juancheng in Shandong reported 195; and Xingcheng and Beizhen in Liaoning recorded 165 and 136 moths, respectively. In Yanchi, Ningxia, a sex pheromone trap captured 253 moths.
Low-age larvae were detected in Northeast and North China.
In late July, egg masses and early‑instar larvae began to be detected in Northeast China, North China, and other regions, with relatively low pest densities and mostly sporadic occurrences. In Aohan Banner, Inner Mongolia, one egg mass containing 30 eggs was collected from a bundle of millet straw placed in a millet field. In Fuxin, Liaoning, four egg masses were found in a 50‑square‑meter area, each bearing 10–15 eggs, along with scattered first‑ and second‑instar larvae. In Chengde, Hebei, the average larval density in millet fields was 0.05 per square meter, with a maximum of 1 individual. In Jinghai District, Tianjin… Corn On field weeds, the larval density was 2–3 per square meter. In some severely affected plots in Heze, Shandong, the incidence of damaged plants ranged from 15% to 38%; in Weifang, the average number of larvae per hundred plants was 2, with a maximum of 14.
Favorable weather conditions in Northeast and North China
According to forecasts from the National Climate Center, during the first and middle parts of August, most of Inner Mongolia, western Northeast China, and much of Northwest China are expected to experience above-normal precipitation. Specifically, southwestern Northeast China, parts of central and western Inner Mongolia, and northeastern Northwest China may see 20% to 50% more rainfall. Such abundant precipitation is likely to favor the occurrence and damage caused by the armyworm.

Source: National Agricultural Technology Center Author: National Agricultural Technology Center