Do not relax pest and disease control during the cotton flowering and boll stage
In recent years, the proportion of Bt transgenic insect-resistant cotton planted has accounted for more than 95% of the total cotton planting area in our province. The promotion of insect-resistant cotton has played a strong role in controlling the occurrence and damage of cotton bollworm in cotton fields, but some pests and diseases should be strengthened in control. Judging from this year's situation, the cotton boll stage is a period when multiple pests and diseases occur and cause damage in an interwoven manner, mainly including...
In recent years, the proportion of Bt transgenic insect-resistant cotton planted has accounted for more than 95% of the total cotton planting area in our province. The promotion of insect-resistant cotton has played a strong role in controlling the occurrence and damage of cotton bollworm in cotton fields, but some pests and diseases should be strengthened in control. Judging from this year's situation, the cotton boll stage is a period when multiple pests and diseases occur and cause damage in an interwoven manner, mainly with the following characteristics:
First, heavy occurrence and many species. According to forecast analysis, cotton pests and diseases this year will occur at a generally moderate-to-heavy level overall, with local areas reaching heavy to severe occurrence. In particular, multiple pests and diseases will cause interwoven damage during the flowering and boll stage, posing a threat to cotton yield. The main ones include cotton aphid, mirid bugs, red spider mite, Verticillium wilt and Fusarium wilt, and late-stage red leaf stem blight, etc. In some areas, cotton bollworm still needs control, especially for self-saved seed, which must not be neglected.
Second, climatic conditions favor the occurrence of pests and diseases. According to forecasts by the meteorological department, June and July will be hot and humid. This stage is also the key period for cotton squaring, flowering and boll setting, and high temperature and high humidity favor the occurrence and spread of cotton Verticillium wilt and Fusarium wilt, often producing the phenomenon of "a field of seedlings dying after a rain."
Third, the pest and disease population in insect-resistant cotton fields has changed. After the large-scale planting of transgenic insect-resistant cotton, the occurrence trend of cotton bollworm has been effectively controlled, but secondary pests and diseases such as cotton mirid bugs and red spider mite have gradually risen and formed new threats. In the late growth stage of cotton, red leaf stem blight induced by potassium deficiency occurs severely, causing premature senescence of cotton and reducing yield.
Fourth, farmers lack sufficient understanding of the insect-resistant effect of insect-resistant cotton. Bt transgenic insect-resistant cotton is not "insect-free cotton." Especially during the third and fourth generations of cotton bollworm in our province, the resistance of insect-resistant cotton has already clearly declined, and the resistance performance is weakest in the reproductive organs of cotton, namely flowers, buds and bolls. There are often some cotton bollworm eggs laid on these reproductive organs that hatch and survive, causing damage. At the same time, insect-resistant cotton has no resistance to cotton aphid, cotton thrips, cotton spider mite, whitefly, etc., and if not controlled, they often cause new damage.
For this reason, it is recommended to carry out the following key control points:
First, cotton bollworm. For insect-resistant cotton varieties, spraying is generally not needed to control the second generation of cotton bollworm. For conventional cotton, control of the second generation of cotton bollworm should be timed during the peak egg-laying period of adults. Control thresholds and application techniques must be well grasped. When the cumulative number of eggs laid on flower buds and bolls per 100 plants reaches 100 eggs for the third generation of cotton bollworm, or there are 10 larvae, chemical control should be carried out. Chlorpyrifos, emamectin benzoate, phoxim, profenofos, endosulfan, etc. may be selected for control. It is advocated to spray botanical insecticides such as matrine or cotton bollworm virus preparations, and to use half-dose tank-mix spraying techniques with the above related insecticides, to reduce pollution and reduce the source of insects for the next year. However, Bt biological preparations are prohibited in insect-resistant cotton fields.
Second, cotton Verticillium wilt and Fusarium wilt. On the basis of doing a good job of chemical seed treatment, the key link of spraying at the early stage of disease onset should be grasped, with spraying once every 10 days, generally about 3 consecutive sprays. Of course, where conditions permit, rotation with gramineous crops for more than 2 years can be carried out. For control agents, fulvic acid salts, ethylicin plus carbendazim, mancozeb, etc. may be selected, and some nutrient types may also be added to improve plant disease resistance.
Third, cotton mirid bugs. For mirid bug control, early control at the appropriate time is advocated. Generally, spraying begins when there are about 3 nymphs per 100 plants at the cotton seedling stage, and large-scale unified control should be carried out during the same time period to bring the damage of the first generation of mirid bugs in cotton fields under control. During the flowering and boll stage, when the number of insects reaches 20-25 per 100 plants, control must be carried out immediately. Acetamiprid, imidacloprid and malathion, chlorethoxyfos, chlorpyrifos, etc. may be selected for half-dose tank-mix spraying. The control time should be before 9 a.m. and after 4 p.m. When spraying, aim at the tender tips, side shoots and buds and bolls. It is emphasized to spray evenly and thoroughly and to carry out large-scale unified control. Be careful not to skimp on water while sparing pesticide, and do not spray when there is dew.
Fourth, cotton red leaf stem blight. It is mainly a disease induced by potassium deficiency. During the flowering and boll stage, cotton grows vigorously and its potassium demand increases greatly. If the potassium fertilizer supply in the field is insufficient, cotton red leaf blight is likely to occur. In conjunction with the control of Verticillium wilt and Fusarium wilt, a 0.2%-0.3% potassium dihydrogen phosphate solution can be sprayed at an early stage, once every 7 days, for 2-3 consecutive sprays. Where conditions permit, formula fertilization techniques can be carried out well, and potassium fertilizer can be supplemented according to actual needs.
Fifth, cotton aphid and cotton red spider mite. For cotton aphid, imidacloprid, acetamiprid, etc. may be selected; for red spider mite, abamectin and organophosphorus pesticides may be selected for half-dose tank-mix spraying.
Note that control of cotton aphid and red spider mite should be carried out before the pests spread from spots to the whole field. If the pest population is very large and has already spread throughout the field, the difficulty of control will increase greatly.