| Mixing pesticide is one of the useful techniques of pesticide application. Though people use pesticide mixture on the production of many kinds of crops, there wasn't much research on the adoption of pesticide mixture on the tobacco. The pesticide is an important measure to guarantee production and quality of Yunnan tobacco, but there exists using pesticide certain blindness still. Some farmers mixed two or more than two kinds of pesticide without pertinence. The results showed that control effect was not good and it caused waste. Sometimes it resulted in phytotoxicity. According to the theory and principle of pesticide blending, we carried out researches indoor and in the fields to test efficacy of pesticide commonly used on tobacco, and the results affirmed 22 kinds of insecticides combinations, 17 kinds of fungicide combinations, 23 kinds of insecticides and fungicide combinations. Part of the combinations were experimented in the field, The results showed that Metriphonate+ deltamethrin, DDVP+deltamethrin, Imidacloprid +carbendazim +dimetachlone), deltamethrin+Dali , Mieyaning +polyoxins were better. Moreover we studied the combined toxicity of mixed pesticides to Myzus persicae (Sulzer), the interaction of fungicide mixtures to tobacco Brown spot, and the postponing effect of mixtures on development of resistance of Myzus persicae to pesticides. The main results of the study are as following:1. Associated Toxicity of Mixed Pesticides to Myzus persicae (Sulzer): The indoor toxicity of 10 mixtures of 9 pesticides to Myzus persicae (Sulzer) were determined by Sun's co-toxicity coefficient. Synergism was found in five mixtures: i.e., lambda-cyhlothrin+DDVP, Mieyaning+Dipterex, Decis+Dipterex, Carbaryl+Dipterex and Kungfu+ Decis. Their co-toxicity coefficients were 822.4, 795.9, 708.3, 400.9, and 307.1, respectively. While antagonism was found for the other five mixtures, i.e., their co-toxicity coefficient were below 100. The synergic mixtures were used to perform further indoor and field trials.2. Interaction of Fungicide Mixtures to Tobacco Brown Spot: According to the results of the two years laboratory screening test mixtures of fungicides, 10 kinds of mixtures showed better control. Synergisms of the mixture were tested by Wedley's method. The results showed that dimetachlone + dimethachion had significantly better control, with synergism ratio(SR) of 1.51. Other two mixtures with additive effect and with SR>1 were: dimetachlone+Baofengning, dimethachion+hebenjunjing, the SR are respectively 1.27,1.13.3. Postponing effect of mixtures on development of resistance of Myzus persicae to pesticides: By selecting experiment on potted plants, five pesticides and three of their mixtures were tested using Myzus persicase as speciesmen. In conditions that the indoor dry-dulb temperature was 27.5℃ and wet-dulb temperature was 25.5℃, population of Myzus persicae was treated with thepesticides and their mixtures. After the selecting of 10 generations rate of resistance for Dipterex, Kungfu, DDVP, Decis, Mieyaning was 1.84, 1.68, 1.47, 1.34, and 1.02, respectively. While the rate of resistance for Dipterex+Decis, Dipterex+ Mieyaning, and DDVP+Kungfu, were 1.15, 1.22, and 1.25, respectively. Index of delay on resistance for the three pesticide mixtures was 2.4476, 0.1600, and 1.6562, respectively. The results indicated that Dipterex+Decis and Kungfu + DDVP could postpone the resistance for Myzus persicae .4. Controlling of Tobacco Aphids with Pesticide Mixture in Fields: Three pesticide mixtures were selected to evaluate their field efficacy against tobacco plantation The trails were conducted at Dali District, Nanjiang County, and in our institute, respectively for 2 years. Their pesticidal activity of the three mixtures was compared with the single components. The results indicated that 5 days after the treatment, the suppressive effect on population was 78.86% for Dipterex+Decis in Nanjian County, with increase of efficacy for 10.5% and 5.84%, respectively, in comparison with Dipterex and Decis alone. The results in our institute indicated that 10 days after treatment, the mixture of Dipterex and Decis had efficacy of 80.32%, with increase of that for 21.42% and 14.08%, respectively, in comparison with Dipterex and Decis alone. The results indicated that Dipterex and Decis were synergistic. Other two pesticide mixtures were tested as well in this study and they didn't show any synergism. By ANOVA, the efficacy of each treatment differed significantly from the control at 0.01 level.5. Experiment on Mixed Pesticides for Controlling of Tobacco Brown Spot in Field: We carried out experiments at Dali and Yuxi to test efficacy of three kinds of fungicide combination. Result: Dali+dimethachlor and Dimethachlor+copperchloride+Hebenjunjing were the same as the single pesticide in efficacy, while Baofengning+polyoxins was not so ideal at the two experimental sites.6. Experiment of Mixed Pesticides against tobacco Brown Spot and Myzus persicae (Sulzer). In order to study the practical efficacy of pesticide mixture on tobacco Brown Spot and on Myzus persicae (Sulzer), plot and indoor experiments were conducted with 5 mixtures of pesticide and bactericide, such as Admire+ Dimethachlon+Carbcndazim, Decis+Dali, Mieyaning+polyoxins, DDVP+dimethachlor, Dipterex+ Dimethachlor+copper, and the relevant pesticide as single .The results showed that two mixtures , i.e. Admire (at dilution of 30000 X)+ (Dimethachlon+Carbcndazim)( at dilution of 500 X) and Decis (at dilution of 2000 X)+ Dali (at dilution of 500 X), had better control against both tobacco brown spot and Myzus persicae (Sulzer). |
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