The Latest Tutorial on Prevention and Control Techniques for Cotton Bollworm
The cotton bollworm is a major pest during the cotton bud and boll stage. It is a species of insect in the genus Helicoverpa, family Noctuidae, order Lepidoptera, and is widely distributed in China and around the world. It occurs in cotton-growing regions and vegetable-growing areas throughout China, with the Yellow River cotton region and the Yangtze River cotton region suffering more severe damage. In recent years it has also occurred from time to time in the Xinjiang cotton region. Let us take a look at the prevention and control techniques for the cotton bollworm!
Damage Characteristics
The cotton bollworm is an important boring pest during the cotton bud and boll stage. It mainly bores into and feeds on buds, flowers and bolls, and also feeds on tender leaves. Adults hide on the undersides of leaves and other places during the day and begin activity at dusk, feeding on nectar. They are phototactic, and eggs are laid singly on the upper part of the cotton plant. The larvae have 5 to 6 instars. First-instar larvae feed on tender leaves, after which they damage buds, flowers and bolls, mostly boring into buds and bolls from the base and feeding inside, and they are able to move to cause damage elsewhere. Damaged young buds have their bracts opened and then drop off, and bored green bolls are easily contaminated and rot. The larvae have the habit of moving between plants to cause damage, mostly at night and in the early morning; applying pesticide at this time makes it easy to contact the insect bodies, giving the best control effect.
Occurrence Pattern
The cotton bollworm has 3 to 4 generations per year in the Yellow River cotton region and 4 to 5 generations per year in the Yangtze River cotton region, overwintering as diapause pupae in the soil. The first generation mainly causes damage in wheat fields, the second-generation larvae mainly damage the growing tips of cotton, and the third and fourth-generation larvae mainly damage cotton buds, flowers and bolls, causing large numbers of damaged buds, flowers and bolls to drop off and greatly affecting cotton yield. In addition to damaging cotton, the fourth and fifth-generation larvae sometimes become major pests on crops such as corn, peanuts, beans, vegetables and fruit trees.
Reproductive Habits
In South China, the cotton bollworm has 6 generations per year, overwintering as pupae in the soil near the roots of host plants, and emerging and laying eggs successively in the following spring. The first generation mostly causes damage on crops such as tomatoes and peas. From the second generation onward, generations overlap in the field. Adults rest on the undersides of leaves or in shaded places during the day and begin activity at dusk, sucking plant nectar as supplementary nutrition. They are strong fliers and phototactic, and have a strong tendency to seek out tender growth when laying eggs. Eggs are laid singly on tender leaves, fruit stalks and other parts of the host. Each female generally lays more than 900 eggs, with a maximum of more than 5,000. Newly hatched larvae rest on the undersides of leaves on the same day without feeding or moving, move to the growing point on the second day but cause no obvious damage yet, become second-instar on the third day and begin boring into and feeding on flowers, tender shoots, tender buds and fruits. They can move between plants to cause damage, and each larva can bore into 3 to 5 fruits. After the fourth instar comes the stage of heavy feeding. Mature larvae enter the soil to a depth of 5 to 15 cm and make an earthen cell in which to pupate.
Prevention and Control Techniques
1. Autumn plowing and winter irrigation: Autumn plowing and winter irrigation can reduce the overwintering insect population base. In autumn, for cotton, corn, tomato and other fields where the cotton bollworm causes severe damage, carry out autumn plowing and winter irrigation and break down field ridges to destroy overwintering sites, increase the overwintering mortality rate and reduce the occurrence of the first generation.
2. Manual collection of insects: Taking advantage of the habit of adult cotton bollworms of preferring to rest and lay eggs in the funnel-shaped leaf whorls of corn, specially assigned workers beat the heart leaves every morning to kill adults and reduce the source of insects. This can reduce the use of chemical pesticides, protect natural enemies and help improve the ecology of cotton fields.
3. Strengthen management: Appropriately control late-stage irrigation and control the amount of nitrogen fertilizer to prevent excessive vegetative growth of cotton, which can reduce cotton bollworm damage. During the adult egg-laying period of the cotton bollworm, spray a 2% calcium superphosphate extract on the leaves; this both has the effect of foliar fertilization and can reduce the number of eggs laid by the cotton bollworm in cotton fields. Top and prune at the right time, and take the branches and leaves out of the field for destruction; this can kill cotton bollworm eggs and larvae and reduce the occurrence of the cotton bollworm in cotton fields.
4. Poplar branch trapping: Taking advantage of the taxis of adult cotton bollworms toward volatiles from poplar leaves and their habit of hiding in poplar branch bundles during the day, placing poplar branch bundles in cotton fields to trap moths during adult emergence and egg-laying is an effective method. Place 6 to 8 bundles per mu, and collect and crush the moths before sunrise. High-pressure mercury lamps and frequency-vibration insect-killing lamps have the characteristics of trapping and killing large numbers of cotton bollworms and causing little harm to natural enemies, and are suitable for use in areas where the cotton bollworm has heavy outbreaks and during the peak emergence period.
5. Chemical control: The prevention and control of the cotton bollworm should mainly use biological pesticides or pesticides that cause little harm to natural enemies. For controlling the second generation of the cotton bollworm, choose 20% methomyl emulsifiable concentrate at 1500 times dilution. For the third and fourth generations, use 48% chlorpyrifos emulsifiable concentrate 50 to 60 ml per mu, mixed with 50 to 60 kg of water for spraying. During the control period for the third and fourth generations of the cotton bollworm, the cotton plants are tall and eggs are scattered, so spraying should be timed from the peak hatching stage of eggs to the young larval stage, and the front and back of cotton leaves, growing tips, flowers, buds and bolls must be evenly covered with the pesticide to ensure efficacy. At the same time, pay attention to alternating and rotating pesticides, and if rain occurs after application, respray in time.