The Dynamics And Integrated Management Strategy Of Disease And Pest In Cotton Field In Dezhou

The status,especially the changes about community of cotton field and species and quantity of diseases and pests after insect-resistant cotton was planted extensively were studied in Dezhou city.The disciplinarian of main disease-pest's appearances was described and a integrated management strategy was set up to control disease and pest in cotton field according to the results of the survey.The results as follows:1.The emergence and status about the diseases of Bt cotton seeding, Fusarium wilt,Verticillium Wilt and Red leaf blight of Bt cotton have been studied based on the research in the cotton fields.At the same time,the characteristics and main factors to happen about diseases and pests have been defined.It was the basis to establish the integrated management strategies. The results showed that Rhiz octoni asol ani of cotton was the main diseases of Bt cotton seeding which could induce damage differently among different kinds of insect- resistant cotton.The insect-resistant cotton from America and its derived varieties incidenced more seriously,because it growed weakly at early stage.Verticillium Wilt of cotton was the most serious in all the kinds of cottons.And even the incidence of VerticilIium Wilt of cotton could reach to 70%in serious fields in the late of July.The reason maybe that lack of effective insect- resistant cotton varieties,weak resistance and growing cottons for many years at the same field may led to Verticillium Wilt of cotton.In addition,Red leaf blight of cotton has often taken place recently instead of happening occasionally in the past.The research indicated it possibly caused by cotton varieties,the content of kalium in soil,previous crop species and so on.2.Systemically compared the dynamic changes about cotton bollworm (Helicoverpa armigera),cotton aphid Aphis gossypii(Glover),cotton capsid, and analyzed the reasons of changing.The results showed that the second generation and third generation cotton bollworm took place seriously before insect- resistant cotton was planted.The occurrence degree of cotton bollworm tends to relief after1998 Bt cottons were planted widely. Through the research we could know that accumulated eggs in the second generation were little differences between Bt cotton and common cotton, however,the quantity of larvae decreased obviously in Bt cotton,however the resistance was very well.The larvae number of the third generation bollworms decreased per 100 cotton plants after transgenic cottons were planted,but the ratio of incubating eggs in the third generation was higher than the second generation.It indicated that the resistance of Bt cottons to the third generation cotton bollworm decreased.The changes of the fourth generation were obvious.The eggs and larvae number of the forth generation bollworms increased per 100 cotton plants,compared with the third generation,which showed that the resistance to the forth generation cotton bollworm decreased gradually.For cotton aphid,its occurrence and damage degree were no obvious difference between Bt cotton and common cotton, which showed that there were no obvious influences on cotton aphid for Bt cotton.Compared with common cotton,the occurrence of Cotton capsid in insect-resistant cotton field was serious.However,at Late Growth Stage of cotton,the quantity of cotton capsid in Bt cotton was less serious than that in common cotton.It was possible that the premature senescence phenomenon at Late Growth Stage of cotton was serious,which limited the occurrence of Cotton capsid.3.The integrated management strategy to control plant diseases and pests of cotton has been proposed through experiments and analysis.The measures as follows:Preemergence There were some measures to control diseases and pests, such as resistant varieties,seeds treatment and cultivation measures,and seeds treatment could use 15%carbendazim·thiram(1:40～1:50) flowable concentrate for seed coating.Seedling stage It should take some measures to prevent diseases and cotton aphids,generally used 50%carbendazim,70%thiophanate-methyl or 10% imidacloprid.Bud and boll stage The key was to control Verticillium Wilt,Red leaf blight, cotton bollworm(Helicoverpa armigera) and cotton capsid.In order to prevent Verticillium Wilt of cotton,we should usually choose resistant varieties,as well as graded fertilizer particularly boll fertilizer.To prevent Red leaf blight of cotton,there were some measures to take,such as to improve soil environment,water and fertilizer managements.If Red leaf blight of cotton took place seriously,it should use 1%-2%Potassium dihydrogen phosphate(solution) or mixed with 1%Urea about 30kg/667Km~2. Of course,Foliar-fertilizeri is a remedial measure.In insect- resistant cotton field,it is not necessary to control the second generation of cotton bollworm. However,the third and fourth generation should be taken some measures to control,using the mixture of 15%Avermectins.Triazophos(micro-emμlsion) about 120g～160g per acreage according to the density.It should pay attention to cotton capsid.If it is necessary,80%Fipronil(emulsifiable concentrate) which was diluted 1500 folds should be sprayed.In addition, using different pesticides alternately was very important to delay the resistance to the pest.