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 high moth‑attracting counts 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. 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 forecast to be from early to mid‑August.
The second-generation armyworm has a large area of occurrence.
Local pest populations are high in the northwest and southwest.
This year, the second-generation armyworm was observed across 35 million mu nationwide, a 15% increase compared to 2020. Overall, the pest situation was moderate, with severe outbreaks in localized areas of Northwest and Southwest China—more intense than both last year and the long-term average. Across the country, 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 reported, 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 remained at 3–5 larvae per square meter, most areas recorded levels 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, second-generation adults have been emerging 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 66–89 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 12–50 moths; and in Heilongjiang, most sites recorded 2–33 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 reported 1,018; Laizhou in Shandong, 287; Shuangcheng in Heilongjiang, 264; and Pingluo in Ningxia, 253. At monitoring lamps: Pucheng and Fugu in Shaanxi logged 518 and 362 moths, respectively; Dameng in Hebei, 303; Urad Front Banner, Left Rear Banner, and Tongliao in Inner Mongolia, 240, 113, and 110, respectively; Shuangcheng, Ning’an, and Jixian in Heilongjiang, 201, 175, and 166, respectively; Juancheng in Shandong, 195; and Xingcheng and Beizhen in Liaoning, 165 and 136, 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 was collected from 20 millet straw bundles, containing 30 eggs. In Fuxin, Liaoning, four egg masses were found in a 50‑square‑meter millet field, each with 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 larva per square meter. In Jinghai District, Tianjin… Corn On field weeds, the larval density is 2–3 per square meter. In some severely affected plots in Heze, Shandong, the incidence of damaged plants ranges from 15% to 38%; in Weifang, the average number of larvae per hundred plants is 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 will likely favor the occurrence and damage caused by the fall armyworm.

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