Study On Sustained-release Fungicide Of Controlling Tobacco Black Shank

Phytophthora parasitica var. nicotianae is one of the most important pathogen causing huge damage to yield and quality of tobacco in recent years. In this study microcapsules prepared reduce pesticide residues, while prolonged persistence of fungicides. Firstly, screened fungicides can effectively control tobacco black shank by bioassay methods; Then investigated the optimum conditions by preparing microcapsules and orthogonal experiment; Finally, surveyed the incidence of tobacco and calculated the disease index and control effect in greenhouse tests. The results as following:1. The conventional fungicides on the field such as metalaxy、dimethomorph、cyazofamid、fluopicolide、pyraclostrobinl and pyrimorph for controlling tobacco black shank were selected and tested strains(phytophthora parasitica var. Nicotianae). The results showed that EC50 of metalaxy, dimethomorph, fluopicolide and pyrimorph were 0.2847μg·ml-1, 0.4563μg·ml-1, 0.1242μg·ml-1 and 1.3614μg·ml-1 So selected metalaxy, dimethomorph, fluopicolide, and pyrimorph preparing microcapsules.2. Metalaxyl dissolved in xylene mixes with water to form a stable O/W emulsion by adding different additives. Screened optimum additives 0203. In the preparation of the microcapsules, in order to clarify the control efficacy of 15 percent of sustained released metalaxyl microcapsules to tobacco black shank disease, we prepared the microcapsules via in-situ polymerization and optimized the preparation process. The release mechanism of metalaxyl microcapsules and their effect on black shank disease was evaluated by greenhouse pot experiment. According to our results, the optimized recipe was as follows: 15% metalaxyl ingredient, 27% xylene, 2.5% 0203, 2% ammonium chloride, 4% ethylene glycol, 0.2% xanthan gum, 2% NNO, and 47.3% water. The preparing parameters were: the core wall ratio, 1:1; speed of stir, 400 r/min; time of adjust acid, 2 h; PH 4.5, respectively. The prepared microcapsules were smooth on the surface, with an average diameter of 12.93μm and a cover rate of 93.58%. The active ingredients of metalaxyl microcapsules were slowly released in the aqueous phase. The quick releasing period was at 0~24 h, which cumulatively released up to 29.52% of total ingredients and was in accordance with the First-level reaction. The uniform releasing period was at 24~360 h, which cumulatively released 29.52%-93.22% and was coincident with Zero-level reaction. The release became stable after 360 h. The microcapsules we prepared showed a high control efficacy of about 82.2% to black shank disease at 21 days after inoculated, which was higher than the 75.7% control efficacy of 25% metalaxyl WP. These results indicated that 15% metalaxyl microcapsules we prepared in this study had a sustained release property and good control effect to tobacco black shank disease.3. Bying situ polymerization, with melamine resin wall, according to the optimum preparation conditions, The four kinds of fungicides for controlling effectivly tobacco black shank screened were made of 15% of metalaxyl microcapsule suspension, 60% of metalaxyl microcapsule powder, 60% of dimethomorph microcapsule powder, 60% of pyrimorph microcapsule powder, 60% of fluopicolide microcapsule powder, and measure their relative performance characterization. The results show that the microcapsule is coating intact, dense, particle size appropriately, distribution evenly, HPLC and infrared analysis showed that the coating is high and the structure is not changed.4. 15% of metalaxyl microcapsule suspension, 60% of metalaxyl microcapsule powder, 60% of dimethomorph microcapsule powder, 60% of pyrimorph microcapsule powder, 60% of fluopicolide microcapsule powder and 72% metalaxyl ? Mn Zn WP, 50% dimethomorph WP pot experiment results show that: although control effect of fluopicolide, pyrimorph is not good, from 21d( 62.6%, 56.0%) to 35d(51.4%, 44.9%) control efficiency is reduced small margin. The control efficiency of 15% of metalaxyl microcapsule suspension, 60% of metalaxyl microcapsule powder, 60% of dimethomorph microcapsule powder is higher than 72% metalaxyl ? Mn Zn WP, 50% dimethomorph WP, the persistence of up to 35 d or more.