How many generations of the boring pest cotton bollworm occur in a year, and how should insecticides be used for its control?

The cotton bollworm, of the order Lepidoptera and family Noctuidae, is widely distributed in China and around the world, and occurs in both cotton-growing and vegetable-growing regions of China. The cotton bollworm is an important boring pest during the cotton bud and boll stage, mainly boring into and feeding on buds, flowers and bolls, and also feeding on tender leaves. So how many generations of the cotton bollworm occur in a year? How to control it? What insecticides to use?

How many generations of the cotton bollworm occur in a year?

The annual number of generations and the main damaging generations of the cotton bollworm differ among the cotton regions of our country. In the Liaohe River basin cotton region and most cotton regions of Xinjiang, 3 generations occur annually, with the 2nd generation causing the main damage; in the Yellow River basin cotton region and some cotton regions of the Yangtze River basin, 4 generations occur annually, with the 2nd generation being the most severe, followed by the 3rd; in most cotton regions of the Yangtze River basin, 5 generations occur each year, with the 3rd and 4th being the most severe; and in areas south of 25°N, 6~7 generations can occur each year, with the 3rd, 4th and 5th generations causing severe damage. In all localities, the pest generally overwinters as pupae in the soil.

How to control the cotton bollworm? What insecticides to use?

In the northern Xinjiang region, the cotton bollworm has now entered the peak period of egg hatching, which will continue until around June 5, and the first-generation larvae are expected to cause damage in cotton fields in early June; the southern Xinjiang region is currently in the period of first-generation larval damage. At this stage, regardless of northern or southern Xinjiang, the focus should be on the prevention and control of the first generation of the cotton bollworm.

Current recommendations for cotton bollworm control in northern Xinjiang:

(1) Northern Xinjiang region: According to simultaneous monitoring with forecast lamps and sex pheromone traps, the overwintering generation of the cotton bollworm has entered the late peak of adult emergence; according to a cotton field survey on May 22-23, the average number of first-generation eggs was 3.9 per 100 plants, with a maximum of 6.4 eggs per 100 plants; the current sex pheromone moth catch is relatively large, with a single sex pheromone cage catching up to 12 moths. Based on the analysis and prediction of the period after heavy rainfall, as temperatures rise, accelerated cotton seedling growth, generally tender or overly vigorous cotton seedlings, and meteorological factors in late May: the peak period of first-generation cotton bollworm larval damage in the field will be in early to mid-June, with a light occurrence level and moderate occurrence in individual cotton fields.

Key technical points for controlling the first generation of the cotton bollworm:

1. Choice of insecticides:

Choose biological pesticides such as cotton bollworm nucleopolyhedrovirus, emamectin benzoate, and Bacillus thuringiensis for pest control, which helps delay pest resistance and protect natural enemies.

2. Timing of application:

(1) The appropriate period for application is the peak of egg hatching and before young larvae begin boring. Spraying at the egg peak can effectively prevent the cotton bollworm from causing damage to the crop. At this time, frequent field surveys are required to obtain accurate forecast information.

(2) Application operations should be chosen after the morning dew has completely dried (8:30~10:00) or after 18:00 in the afternoon.

3. Requirements for application quality:

Spray evenly over the middle and upper parts of the cotton plants, with a water volume of 30~40 liters (the water volume should not be too large), ensuring a reasonable spray concentration to improve efficacy.

Current plant protection work recommendations

1. Attach great importance to the monitoring and control of cotton mirids. Strengthen surveys of cotton fields with overly vigorous growth and early budding, grasp the critical period for control, apply pesticides in the evening, and use a mixture of acetamiprid and abamectin, firmly carrying out joint prevention and control to keep the cotton bud damage rate below 2%.

2. In controlling the cotton bollworm, make full use of green control methods such as sex pheromone cages to concentrate moth trapping; forecast and monitoring points should carry out full-process monitoring to truly reduce the pest population and ease control pressure.

3. For cotton spider mites, strengthen surveys both inside and outside the field, adopt comprehensive control measures, and keep the pest source base to a minimum; for cotton aphids, carry out monitoring and control work well. Yellow boards should be placed along the roads at monitoring points. When cotton aphid migration is detected, densely place yellow boards in cotton fields to reduce and delay cotton aphid damage; for cotton fields with early cotton aphid center plants or small spot occurrences, insert clear markers promptly and achieve spot-by-spot control.