This year, the first generation of armyworms has emerged earlier and exhibits multiple peak periods; in northern regions, timely monitoring of the second-generation armyworm is essential.

Recently, adult moths of the first generation have been emerging one after another across the Jianghuai, Huanghuai, North China, Northeast China, Southwest China, and Northwest China regions. Eggs have begun to appear locally, while in most areas moth populations have surged earlier than usual, with multiple peak periods; overall moth densities exceed those of the same period in 2015 and 2016. Taking weather conditions and crop‑planting patterns into account, the second generation of armyworms is expected to occur at a moderate level nationwide this year. In localized areas of Hebei, Shaanxi, Inner Mongolia, and other regions with abundant rainfall and lax management, high‑density infestations may develop. Meanwhile, in much of Henan, as well as in parts of northern Jiangsu and Anhui where wheat straw is plentiful and field humidity remains high, vigilance is advised against the persistence of second‑generation armyworms and their subsequent damage. The total affected area nationwide is projected to be approximately 30 million mu, with the peak period of larval feeding and damage occurring from late June to early July.

1   The first-generation armyworm larvae have a small infested area, but local residual pest densities are high.

This year, the area infested by the second generation of the armyworm in the middle and lower reaches of the Yangtze River, the Jianghuai region, and the Huanghuai wheat-growing area totaled 5.14 million mu, down 2.5% and 19.7% from 2017 and 2016, respectively. Nationwide, the average pest density in wheat fields was 0.6 larvae per square meter, a 42.8% increase compared with 2017. The total area treated—either for control or integrated management—reached 8.7 million mu, helping to reduce the initial pest population. Following control measures, the average residual pest density across all regions and field types fell to 0.3 larvae per square meter, close to the levels observed in 2016–2017; however, localized densities remained high—for example, in Yicheng, Hubei, the post‑treatment average across all field types was 6 larvae per square meter, 1.27 times the long-term mean.

2   In most areas, the peak emergence of first-generation adults occurred earlier and featured multiple peaks, with overall moth populations remaining relatively high.

Recently, the first‑generation adult emergence dates across various regions have been earlier than usual for this time of year, with a sudden surge in moth numbers occurring sooner and multiple peak periods. For example, in Zhaozhou, Heilongjiang, the first‑generation adults were first recorded under light traps on May 13, six days earlier than the long‑term average; Lindian accumulated 30 moths, with a peak day count of 22. In Henan, locations such as Xun County, Qinyang, Changge, Yongcheng, and Pingyu all reported single‑day peak catches exceeding 100 moths, with cumulative totals surpassing 300; the peak‑day counts were 3 to 9 days earlier than normal for this period. In most monitoring sites in Hebei, a sharp increase in moth numbers was observed from May 24 to 27, 3 to 5 days ahead of the usual schedule; in Daming, Yongnian, and Ningjin, cumulative totals reached 201, 156, and 110 moths, respectively, with peak‑day counts of 140, 43, and 65. In Tengzhou, Shandong, the cumulative total stood at 157 moths, with a peak‑day count of 58; elsewhere, most sites recorded cumulative catches below 100. In Xingping, Shaanxi, the cumulative catch was 179 moths, with a peak‑day count of 79. In Lishu, Jilin, the cumulative catch was 50 moths, with a peak‑day count of 20.

On some high-altitude light-trap monitoring sites, the days when moth populations surged also occurred earlier and were more abundant than in the previous three years. In Fengtai, Anhui; Mengzhou, Henan; Changdao, Shandong; Luan County, Hebei; and Shuangcheng, Heilongjiang, such surge days were recorded successively from May 16 to 18—about ten days earlier than usual. By May 31, Fengtai, Mengzhou, and Changdao had already experienced two to three peak days; with the exception of Changdao, where the peak-day moth counts were markedly lower than the previous year, and Mengzhou, where they fell short of 2015 levels, the peak-day moth counts at most other sites exceeded those of 2015–2017 (see Table 1). In Xinyang, Henan, 3,800 moths were recorded on May 20, and in Luohe, 530 moths were counted on May 21—more than fifteen times the numbers observed in the preceding two years.

Table 1: Summary of Sudden Increases in the Number of Armyworm Moths at Selected High-Altitude Observation Sites

3   Second-generation eggs have been observed in some areas of Northeast China.

Recently, in some parts of Northeast China, grain‑grass bundles have attracted second‑generation armyworm egg masses, or egg masses have been detected directly in the fields—about a week earlier than in previous years. In Tongliao, Inner Mongolia, on May 20, 20 grain‑grass bundles captured 21 egg masses, with individual masses containing as few as 22 eggs and as many as 350; on May 21, a survey of 30 square meters of wheat field revealed two egg masses. In Gongzhuling, Jilin, 40 grain‑grass bundles yielded 2 and 17 egg masses on May 26 and May 29, respectively, while in Changling, Jilin, grain‑grass bundles also captured multiple egg masses on May 29. In Jianping and Kaiyuan, Liaoning, 20 grain‑grass bundles on May 29 attracted one and six egg masses, respectively, with average egg counts of 120 and 37 per mass. In Zhangwu, Liaoning, a survey of 100 square meters of wheat field on May 31 found 20 egg masses, averaging 31 eggs each, and some of these masses already showed newly hatched larvae.

4   Weather conditions are unfavorable for the occurrence of armyworms across most of Northwest and North China.

According to forecasts from the National Meteorological Administration, in June, southwestern Inner Mongolia, central and eastern Gansu, Ningxia, most of Shaanxi, western Shanxi, northern Sichuan, and parts of northwestern Chongqing are expected to experience above-normal precipitation, while most of North China and the Huanghuai region will see normal rainfall—conditions that are relatively favorable for the occurrence of the second generation of the armyworm. However, much of Heilongjiang, most of Jilin, and northeastern Liaoning are likely to receive 20%–50% less precipitation, and temperatures in eastern Inner Mongolia, Heilongjiang, Jilin, and northern Liaoning are expected to be 2°C–3°C higher than average, which may exert some adverse effects on the development and damage caused by the second-generation armyworm.

In response to the recent sharp increase in the early emergence of armyworm moths, coupled with high moth populations, and in northern regions… Corn In situations where crop seedlings are small and exhibit weak resistance to damage, all localities should attach great importance to the issue, strengthen monitoring, conduct thorough surveys of eggs and larvae in the fields, closely track the dynamics of armyworm outbreaks, promptly issue local pest‑forecast bulletins, and provide comprehensive guidance on timely control measures to prevent large‑scale, concentrated damage.

Author: Pest and Disease Monitoring and Forecasting Division, National Agricultural Technology Extension Service Center Source: Pest and Disease Monitoring and Forecasting Division, National Agricultural Technology Extension Service Center