The transgenic Bt cotton is a new cotton variety that was developed using modern biotechnology to introduce the Bacillus thuringiensis (Bt) insecticidal protein gene into cotton plants. As the transgenic Bt cotton can produce insecticidal protein itself, it has better resistance to lepidopteran pests such as cotton bollworm, reducing the amount of chemical pesticides used and the number of uses, reducing the cost of cotton, reducing the pesticide on farmland The destruction of the ecosystem has been generally welcomed. However, due to the wide variety of Bt transgenic cottons, the differences in insect resistance between different varieties are quite different. In addition, propaganda is misleading, and cotton farmers believe that “insect-resistant cotton†is “insect-free cotton†and does not require medication control, resulting in some Insect-resistant cotton has poor resistance, heavier occurrence of cotton bollworm, and serious non-target pests. In view of the problems existing in the production of insect-resistant cotton, the characteristics, existing problems, and comprehensive prevention and control techniques of pest-resistant weeds are briefly described below. The characteristics of insect-resistant cotton: 1. Insect resistance mechanism: Transgenic Bt cotton can continuously produce insecticidal protein in the whole growing season of cotton. This insecticidal protein spreads in various parts of the plant, and lepidopteran pests such as cotton bollworm feed on it. After the insect-resistant cotton, its digestive system was damaged and it could not be eaten. The body was soft rot and eventually died. In addition, insect-resistant cotton can produce a variety of pest nuisances and unpleasant odors that can protect or reduce pest damage. 2. Scope and effect of insect resistance: Transgenic Bt cotton has good resistance to lepidopteran pests such as bollworm, red bollworm, corn borer and bridge-building insects. No resistance to other pests, diseases, and weeds in cotton fields. The second generation of Helicoverpa armigera has better insect resistance, and its insect resistance to the third and fourth generations of Helicoverpa armigera is significantly reduced. When the amount is large, it must be controlled by chemicals to control its damage. 3. Impact on the cotton field ecosystem: Due to the delay in drug use time and the decrease in the number and dosage of the Bt gene-resistant cotton, the killing effect on natural enemies is reduced, which contributes to the establishment of natural enemies in the cotton field and the exertion of natural control functions, and reduces The harm of pests. There are many problems in transgenic Bt cotton: 1. Variety of species, market confusion, and differences in insect resistance of different species. As the transgenic Bt cotton has good resistance to cotton bollworm, the planting area has expanded rapidly and the demand for cotton seed has soared. Many units that do not have seed production ability are driven by high profits, resulting in the occurrence of counterfeit and inferior insect-resistant cotton. 2. Cotton bollworm can also produce resistance to transgenic Bt cotton. Since the Bt gene-resistant cotton did not transfer the Bt strains of several insecticidal protein genes into the plant body, the resistance rate of the cotton bollworm to the insect-resistant cotton was significantly higher than that to the Bt insecticide. speed. At present, the insect-resistant cotton planted in the production is mostly a transgenic insect-resistant cotton, and the cotton bollworm is relatively easy to produce resistance. However, the risk of developing resistance to transgenic bollworms is much less. 3. The resistance of Bt transgenic cotton to cotton bollworm in cotton at different growth stages is quite different. The results of the study showed that the transgenic Bt cotton had a high amount of insecticidal protein gene in the early growth stage, ie seedling stage and bud stage, and had strong resistance to cotton bollworm. Therefore, the transgenic Bt cotton has good control effect on the second generation of cotton bollworm, and does not need to be controlled in the year of occurrence. The control effect on the third and fourth generations of cotton bollworm is weak, and it is necessary to strengthen monitoring and carry out chemical control as appropriate. In addition, under the condition of high temperature and drought, the amount of insecticidal protein gene in Bt transgenic cotton was low, and the insect resistance effect was not obvious. 4, Bt transgenic cotton is not insectless cotton. The transgenic Bt cotton only has resistance to lepidopteran pests such as cotton bollworm, red bollworm, bridge-building moth, corn borer, etc., to cotton aphid, cotton leafhopper, cotton thrips, cotton blind cockroach, leafhopper, white powder The sucking pests such as cockroaches not only have no resistance, but are beneficial to their serious occurrence. Comprehensive control measures for pests and weeds in Bt transgenic cotton fields: Prevention and control of pests and weeds in transgenic Bt cotton should start from the overall ecological system of the cotton field, coordinate the use of agricultural control, biological control, and chemical control measures to harm the pests and weeds. Control is below the economic threshold. 1. Seeding period (late April to mid-May): Seed dressing or comprehensive seed dressing before sowing to prevent seedling diseases and underground pests. 2, seedling period (mid-May to early June): to control seedling mites, cotton thrips, underground pests, blight, weeds. When cotton seedlings are transplanted, they can be applied to or applied with iron, exogenous iron, carbofuran, and chelated granules to prevent and control underground pests, as well as seedlings, cotton leafhoppers, and thrips. Covering the cotton fields with mulch film, it can be sprayed before the filming of ridges to prevent herbicides at the seedling stage by spraying herbicides such as dole, quince, and acetochlor. In areas of dry and verticillium wilt recurrence, it can be controlled by spraying and root irrigation with Stirling and Gwangling during the initial stage of cotton seedling disease. 3. Flower bud period (mid-June to mid-August): The focus of prevention and control during this period is sucking pests (cotton aphid, cotton leafhopper, cotton blind locust, cotton leafhopper, whitefly), three generations of cotton bollworm, beet Night moth, blight, Verticillium wilt, weeds and so on. The control of cotton leafhoppers can be sprayed with 0.9% chlorfenadine EC 3000 times solution or 15% broom net EC solution 2000 times solution. 4. Boll period (from mid-August to late September): It is mainly used to prevent and control four generations of Helicoverpa armigera, Spodoptera exigua, and some sucking pests and boll diseases (cotton boll disease, red rot, pinkish pink, anthracnose). The insect resistance of Bt transgenic cotton is weakened in the later period. When the fourth generation of cotton bollworm has a large amount, it must be controlled. Artificial release of Trichogramma or spraying of NPV virus preparations can be used for biological control, and if necessary, compounded chemical pesticides are used. In the late growth stage of cotton, due to the large cotton plant and the hot weather, pests are dispersed on the cotton plant, and the spraying liquid volume should be increased during application. Pay attention to rotating medications, mixed medications, try not to use pyrethroid pesticides in the later period, so as not to increase the resistance of pests such as cotton bollworm and aphids in the following year.
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