Shandong: The area expected to be affected by the second generation of cotton bollworm is estimated at approximately 2.1 million mu.

Release Date:

2019-06-11

The forecast predicts moderate incidence of the second generation of cotton bollworm in Shandong Province, with slightly lighter infestations in the eastern part of the northern Shandong cotton-growing region. The affected area is estimated at approximately 2.1 million mu, with the onset of the pest’s activity occurring earlier than usual but roughly on par with the same period last year. In the major cotton‑growing areas, the peak emergence of first‑generation adults is expected from June 10 to 29. Starting June 12, all cotton regions will gradually enter the peak egg‑laying period of the second generation; in southwestern Shandong, the peak egg‑laying date typically falls around June 20, while in other cotton‑growing areas it is expected around June 25. The optimal window for control measures is anticipated to begin around June 18. Thanks to the use of insect‑resistant cotton varieties, the population of cotton bollworm larvae in cotton fields will remain at low levels, resulting in relatively minor damage to cotton crops; however, this may pose a greater threat to peanuts, corn, vegetables, and…

The forecast predicts moderate incidence of the second generation of cotton bollworm in Shandong Province, with slightly lighter infestations in the eastern part of the northern Shandong cotton-growing region. The affected area is estimated at approximately 2.1 million mu, with the onset of the pest’s activity occurring earlier than usual but roughly on par with the same period last year. In the major cotton‑growing areas, the peak emergence of first‑generation adults is expected from June 10 to 29. Starting June 12, all cotton regions will gradually enter the peak egg‑laying period of the second generation; in the southwestern Shandong cotton belt, the peak egg‑laying date typically falls around June 20, while in other regions it is anticipated around June 25. The optimal window for control measures is expected to begin around June 18.

Thanks to the use of insect-resistant cotton, the population of cotton bollworm larvae in cotton fields will remain at a low level, resulting in relatively mild damage to cotton. However, the harm to off‑field crops such as peanuts, corn, vegetables, and soybeans is trending upward. Cotton‑growing regions—particularly those in southwestern and northern Shandong—should strengthen monitoring and implement timely control measures.

Forecast basis:

1. In the major cotton-growing regions, the number of surviving first-generation pests is higher than both last year’s level and the long-term average for this time of year. According to surveys at various monitoring sites, the weighted average larval density per mu across all crops ranges from approximately 15.8 to 133 larvae, with a provincial average of 61.97 larvae—exceeding both the figure for the same period last year (41.3 larvae) and the long-term mean (55.58 larvae). At most monitoring points, pest densities are above the long-term norm: in the southwestern Shandong cotton region, the Heze site recorded 81.34% higher than usual, Dingtao 59.3% higher, Jining 51.5% lower, Chengwu 8% higher, and Yuncheng 7.11% higher; in the northern Shandong cotton region, Zouping was 47.45% lower than normal, while Binzhou was 22.3% higher; in the northwestern and eastern Shandong cotton regions, Xiajin was 42.69% lower than usual, Linqing 75.7% lower, Weifang 11% higher, and Gaomi 32.1% above the long-term average.

2. The developmental progress of the larvae is slightly earlier than usual and on par with the same period last year. Based on larval instar surveys conducted at all monitoring sites from May 24 to June 3, the proportions of larvae in instars 1 through 6 were 0.97%, 9.34%, 23.99%, 27.17%, 25.35%, and 12.87%, respectively. Currently, the peak periods for fourth-, fifth-, and sixth-instar larvae are underway, with development progressing marginally earlier than both last year and the long-term average for this time of year (which were 1.33%, 8.80%, 16.87%, 25.39%, 32.54%, and 8.83% during the same period last year).

3. Meteorological conditions have been relatively favorable for the occurrence of the cotton bollworm. During the 2018/2019 winter, Shandong Province experienced above‑normal average temperatures and slightly below‑normal precipitation, creating winter conditions conducive to the safe overwintering of the cotton bollworm. In spring, the province’s average temperatures were higher than usual, which was advantageous for the emergence and subsequent growth and development of the overwintering generation. At monitoring sites across the province, the earliest first appearance of overwintering adults occurred on April 7, close to the level recorded during the same period last year; in most cotton‑growing areas, the onset of adult sightings was broadly consistent with long‑term averages, typically falling between mid- and late April. In May, major cotton‑producing regions of Shandong saw temperatures above normal and markedly reduced rainfall, conditions that favored the emergence of the first generation of cotton bollworms. According to forecasts from the Provincial Meteorological Center, in June, most cotton‑growing areas in Shandong are expected to experience above‑normal temperatures and below‑normal precipitation, with meteorological conditions favorable for the growth and development of the cotton bollworm and for the survival of newly hatched larvae.

4. Cotton growth conditions are relatively favorable for the cotton bollworm, whereas insect-resistant cotton is less conducive to its occurrence. In the major cotton-growing regions, cotton stands are in good condition; statistics show that this year, first-class cotton fields account for 58.3% of the total cotton acreage in Shandong Province. Favorable host plant development promotes concentrated oviposition by the cotton bollworm, increasing egg‑laying rates. At present, more than 99% of the cotton acreage in Shandong is planted with insect-resistant varieties; these cultivars exhibit strong resistance during the early growth stage, thereby suppressing cotton bollworm populations.

5. The structure of cotton cultivation has shifted, and the damage caused by the cotton bollworm to non‑cotton crops is on the rise. In recent years, the area under cotton cultivation in Shandong Province has declined annually, while the proportion of intercropped and relay‑cropped areas has steadily increased. This diversified cropping system provides favorable ecological conditions outside cotton fields for the cotton bollworm to reproduce and inflict harm, leading to a growing trend of damage to non‑cotton crops such as peanuts, soybeans, vegetables, and corn. At the same time, the cotton bollworm’s expansion into non‑traditional cotton‑growing regions is also becoming increasingly evident. The continued reduction in cotton acreage further facilitates the concentrated impact of this pest.

Source: Shandong Provincial Plant Protection Station

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