Cotton has long bearing period and the habit of growing infinitely. In the lengthy bearing period of cotton, it is often damaged by various plant diseases and insect pests. At present yielding condition, the economic loss of cotton will be 5%-15% due to plant diseases and insect pests. If no prevention and control measure is taken, the loss can be 30%-50%. A few plant diseases and insect pests can cause the loss of above 80%. Since the pesticide is invented, it plays an important role on preventing and controlling plant diseases and insect pests, efficiently controls the damage of plant diseases and insect pests, and increases the output of crops. But as the pesticides are applied in long term and big volume, the ecological balance is destroyed and the environment is polluted. This leads to the rampancy of plant diseases and insect pests and increases the difficulty of prevention and control. Therefore, the prevention and control of plant diseased and insect pests of crops must be comprehensive, especially that of cotton, because the plant diseases and insect pests of cotton is severe, and the dosage of pesticide is great.
1) Comprehensive prevention and control of the diseases in seedling stage
The seedling diseases of cotton are mainly prevented and controlled by comprehensive measures, with agricultural prevention and control as the primary measure. This is to control the incidence of seedling diseases and cultivate healthy seedlings. Here we discuss the prevention and control measures of cotton seedling diseases, taking the seedling diseases of the nutrition pot seedbed as an example.
i. Prepare and make the seedbed
Choose the pot soil: The nutrition pot seedbed should be set in a lee and sunny place. The pot soil should be without disease so that the cotton seedlings can grow well. The incidence of blast will be alleviated, and the spreading rate of blast will be slowed. The disease-free soil is usually the soil on the bleachery, in the pond before winter, in the kaleyard or in the healthy cotton field. The nutrition pot should not be made at the incidence center of the blast in the cotton field.
Apply fertilizers to the pot soil: the pot soil should be nutritious soil. The pot soil should be applied ammonium bicarbonate for 25kg/mu, phosphorous fertilizer for 25kg/mu, and potassium fertilizer for 10kg/mu.
Make the pot to be planted: the pot is usually made in sunny days between late March and early April. The nutritious pot is mid-sized. The pot should be placed levelly. The seedbed is 1.2m wide and about 10m long so that it can be covered by film. Cover the base of the pot with earth. Dig ditches around the seedbed. The ditch should be deeper than the base of the pot for water straining.
ii. Seed disposal
The pathogen on the cotton seeds is the main source of seedling disease. Therefore, it’s an important measure to kill the pathogen on the seeds to prevent and control the seedling diseases.
Seed selection and sunning: Select the seeds before seeding. Pick out the seeds with worms, shriveled seeds and broken seeds. Sun the seeds for 2—3 days before seeding to improve the germination vigor of the seeds.
Seed dressing with medicaments: Choose finished seeds dressed with seed coating agent; semi-finished seeds should be dressed with 0.5%-1% zinc methane arsenate or soaked with tolelofos-methyl 200 times diluent for 5—6 hours.
iii. Seedbed management
Apply soil dressing in sunny days, usually in early April. Before soil dressing, the nutritious pot should be watered with zinc methane arsenate 1000—1500 times diluent or tolelofos-methyl 1000 times diluent. Plant 1—2 seeds in each pit. Cover the pot with fine earth after seeding. Make a bow with bamboo sheets and cover the pot with film.
Remove the film to ventilate and exercise the seedling. When more than 80% of the seedlings emerge, and the cotyledons open, the films can be removed in sunny days between 9am to 4pm. This is to shed moisture, ventilate and exercise the seedlings. Uncover the two ends at first and remove the whole film after two days to exercise the seedlings. Cover the seedlings with film at night and when it is rainy or cold to prevent frostbite.
Apply pesticides to prevent disease and ensure the seedlings are healthy. When the seedlings reach full stand, various seedling diseases will happen due to the high temperature and high humidity under the film, and the seedlings will be weak and die. Rhizoctonia disease and anthracnose are the first to happen. When the euphylla emerges, damping-off will happen in great amount, causing the seedlings to die. Necrosis will also happen widely, damaging the leaves to affect the photosynthesis so that the seedlings are weak.
For the diseases on the base of cotton seedlings (Rhizoctonia disease, anthracnose, etc.), splash zinc methane arsenate 1000 times diluent or tolelofos-methyl 500 times diluent on the seedbed together with water. For diseases on leaves, spray half quantity bordeaux liquid (the proportion of bluestone, calcium oxide and water is 0.5:1:100) or 500 times carbendazim or tolelofos-methyl diluent on the leaves. The pesticides should be applied 2—3 times in the whole seedbed stage.
Irrigate adequately to alleviate the incidence of diseases. For the managing of nutritious pot seedbed, it should be avoided to water too much. The seedbed should be “dry” with the surface soil being “white”.
Move the pot and harden the seedling to prevent damping-off and urge the seedling to emerge early. Sometimes when the incidence of damping-off is severe, it’s hard to be controlled by pesticides. The only way is to move the pot. When the first euphylla grows one leaf and one cardiac lobe, the pot can be moved. Remove sick, weak and dead seedling pots. Cover soil on the pot again after moving the pot and apply adequate fertilizers.
2) Comprehensive prevention and control of the plant diseases and insect pests on the early bearing stage of cotton
On the basis of comprehensive prevention and control of the insect pests of cotton, the prevention and control strategy of can be decided. The strategy is: according to the bearing characteristics and the incidence of insect pests, protect and utilize natural enemies and exert the compensation of the cotton on the early bearing stage of the cotton (the dividing line is late July when it is hot and dry). In the florescence of cotton, chemical pesticides are mainly applied to protect the cotton boll.
i. Make best use of the natural enemies and the compensation of the cotton. There are many types of natural enemies in the cotton field that can control the insect pests of cotton, such as spider, ladybug, minute pirate bugs, lacewing fly, Scolothrips takahashii Priesner, etc. these natural enemies can control some main insect pests of cotton, especially cotton aphid and cotton bollworm. In the early bearing stage, the compensation of cotton is strong. When the cotton is damaged by pests or diseases, the buds and flowers will fall off. In certain scope, this will not cause the cotton output to decrease, and can urge the cotton to generate more bolls. Therefore, the above two points should be considered in the prevention and control of early stage pests. The natural enemies should be protected by adequately applying pesticides.
ii. Relieve the damage degree of blast by prevention and control. For the infected fields where the infected breeds are still planted, comprehensive prevention and control measures should be taken to alleviate the damage degree. First is to dig deep ditches to prevent waterlogging; secondly, apply pesticides and irrigate when transplanting the cotton on the basis of seedling cultivation in non-disease soil, pour 100ml carbendazim 1000 times diluent plus carbamide 100 times diluent per plant after the cotton is transplanted into the nutritious pot intraday or the next day; thirdly, add ammonium bicarbonate to the infected cotton plant to kill the virus and urge the plant to grow (pour 400ml ammonium bicarbonate 20—30 times diluent each plant).
iii. Apply pesticides adequately to control the damage of early stage pests.
Cotton aphid: In trefoil stage, when the plants with curled leaves account for 10% of the total plants, the ratio between beneficial insect and aphid is above 1:100, or from trefoil to seven foil stage, when the plants with curled leaves account for 20% of the total plants, the ratio between beneficial insect and aphid is above 1:100, the cotton aphid should not be prevented and controlled after the cotton plants generate buds. The pesticides such as Imidacloprid and Abamecthin should be applied so as to protect the natural enemies.
Red spider: When more than 15% of the plants have pests in seedling stage and 20% in budding and flowering stage, specialized acaricides should be chosen such as biological pesticides like Liuyangmycin and abamectin, chemical pesticides like Pgridaben, etc.
Blind stinkbug: The early cotton field is mainly damaged by second-generation blind stinkbug. When there is more than 10 blind stinkbugs on every 100 plants, organic phosphorus pesticides should be applied such as Imidacloprid or Fipronil. Mass treatment should not be applied.
First generation pin bollworm: In the early cotton field with more than 3 big buds within 200m to the common cotton field or village, when there are above 100 eggs in every 100 plants, pyrethroid pesticides should be applied. BT transgene pest-resistant cotton don’t need to prevent and control pin bollworm.
1—3 generation cotton bollworm: Some vegetable crop field such as tomato field, capsicum field and beanpod field should prevent and control first generation cotton bollworm; second generation cotton bollworm should be prevented and controlled in early cotton field and intercropped/interplanted crops. For common cotton field, when there are more than 10 2—3 generation pest eggs on every 100 plants, pesticides should be applied. The target of prevention and control is to reduce the base of the fourth and fifth generation. BT transgene pest-resistant cotton don’t need to be applied prevention and control measures. For the early stage of 1st, 2nd, 3rd generations, biological cotton bollworm NPV should be applied. The area where BT transgene pest-resistant is planted should not be applied BT agents.
3) Comprehensive prevention and control in flowering stage and bolling stage. The compensation of cotton is weaker from August. The type of plant diseases and insect pests are obviously different with the early stage. The control of natural enemies to insect pests is weaker. The second and third generation pin bollworm and fourth, fifth generation cotton bollworm are the main insect pests at this stage. These insect pests directly cause damage to the harvest of cotton. If the prevention and control measures are misplayed, the cotton output will be greatly reduced. For some years when it rains much in autumn, the cotton may be totally damaged by fourth and fifth generation blind stinkbug if no pesticide is applied on the field. Therefore, the prevention and control in this stage should be based on pesticide prevention and control. According to the traits of the insect pests in recent years, cotton bollworm and cotton leafworm should be mainly controlled, with other insect pests being controlled concurrently. For the boll diseases, agricultural prevention and control should be mainly applied, with pesticides being applied concurrently.
i. Cut empty branches and pick rotten bolls to alleviate boll diseases. When the cotton emerges early and it rains much in autumn, the boll diseases will be severe, due to high humidity and insufficient illumination. Therefore, empty branches should be cut to increase air and light permeability between cotton plants to alleviate the incidence of boll diseases. Rotten bolls should be picked, peeled and sunned to reduce the loss. Pesticide prevention and control of boll diseases can only alleviate the incidence degree, without totally controlling its incidence. From mid August, some pesticides like 70% mancozeb can be applied on the mid and lower part of the cotton plant once every 7days for 3—4 times. The boll disease can be controlled by 50%--60%.
ii. Adequately apply physical and biological prevention and control. During the incidence of 3—5 cotton bollworm, when the incidence degree is above mid level, Jiaduo frequency vibration insect-killing lamp or high pressure mercury vapour lamp can be used in mass cotton field. Poplar branch bundles can be used to trap the moths in dispersed cotton fields. Moth-trapping measures can reduce the eggs laid in the fields by cotton bollworms and pin bollworms, so that the incidence degree of cotton bollworms and pin bollworms can be reduced.
When condition permits, biological measures can be taken to prevent and control cotton bollworm and pin bollworm, controlling the damage of insect pests by manually releasing trichogramma or jewel wasps.
iii. Chemical pesticide prevention and control should be applied scientifically, with the key point of protecting the bolls and buds.
Main target of prevention and control: BT transgene pest-resistant cotton field. In mid and late stage of cotton growing, the main insect pests to be prevented and controlled are red spider, cotton leafworm and blind stinkbug. In common cotton field, the main insect pests are cotton bollworm, pin bollworm, cotton leafworm and blind stinkbug.
Standard of prevention and control
Red spider: 30% of the plants are with pests and red leaves before Aug. 20.
Blind stinkbug: 10 insects for every 100 plants
Cotton leafworm: 30 fourth generation young larvae for every 100 plants
Cotton bollworm: 10 young larvae every 100 plants in pest-resistant cotton field; 30—50 eggs every plant or 3—5 young larvae every 100 plants in common cotton field.
Pin bollworm: 4 green bolls for above 30 days in single second generation plant of common cotton field, 80 eggs in every 100 plants within one day; 4 green bolls for under 30 days in single third generation plant, 300 eggs in every 100 plants within one day.
Prevention and control pesticides: There are many types of pesticides at present. The pesticides are often mixed and compounded at hazard. The pesticides should be applied safely and reasonably to ensure the effect of prevention and control.
Except for choosing right types of pesticides, the pesticides should be applied at right time, on right part and at right dosage. For mid and late stage prevention and control, the dosage should be no less than 60kg when the pesticide is sprayed with manual sprayer, and no less than 15kg with mechanical sprayer.
Technology support: National Agro-Tech Extension & Service Centre