Study On The Occurrenc And Control Of Weeds In Mechanized Transplanting Rice

This study was focused on the occurrence, damage and control of weeds which in mechanized transplanting rice of Jiangsu Province. The occurrence of weeds in mechanized transplanting rice and other cultivation methods were compared in the field trials, and the effect of Echinochloa crusgalli var. Zelayensis on rice was investigated. The measures of agricultural control, including wheat straw returning and water depth were studied in this paper. The susceptibility of weeds in mechanized transplanting rice to different herbicides used frequently in rice field were assayed in laboratory, and screened out new herbicides mixtures to control weeds effectively. Results obtained were listed as following:1、 Occurrence and DamageThe results showed that two emergence fastigium of weeds in mechanized transplanting rice were 5 to 15 days,20 to 25 days after transplanting, and the number of weeds was up to 64.73 plants in 1 m-2. Weeds were more serious in direct-seeding rice fields than mechanized transplanting rice, and less in artificial transplanted rice fields. The emergence fastigium in mechanized transplanting rice was similar with artificial transplanted rice fields, but was a week later than direct-seeding rice. Echinochloa spp. and Leptochloa chinensis (L.) Nees were the main weeds in artificial and mechanized transplanting rice followed by Scirpus planiculmis Fr. Schmidt., Heleocharis plantagineiformis Tang et Wang, Eclipt a pro strata L., and other broadleaf weeds at least. Occurrence of weeds in water direct-seeding rice were the following in turn:Echinochloa spp. and L. chinensis, E. prostrata and other broadleaf weeds, Cyperus difformis L. and other Cyperaceae weeds. Moreover, Echinochloa spp.、 L. chinensis and Digitaria sanguinalis(L.)Scop.in dry direct-seeding rice was more serious than Commelina communis L. and C. difformis.Rice yield was significantly reduced by E. crusgalli var. Zelayensis with 2 plants-m"2. Based on the equation (y=-0.3226x2+9.3785x+1.7792; R2=0.9411; x:density of E. crusgalli var.Zelayensis; y:rice yield), the theory loss rate of rice would be reduced 5%-10% with 0.4-0.8 plants-m-2. And the rice yield was reduced with the decrease of panicles, spikilets per panicle, setting percentage. When the density of E. crusgalli var. Zelayensis was 2 plants·m-2, the effective tillers of rice were reduced significantly. The plant dry weight, spikilets per panicle, spike length, secondary branch stalk and its total grains were reduced significantly but first branch stalk and its total grains with 4 plants·m-2. Setting percentage, high leaf area were significantly reduced with 8 plants·m-2.2、 Agricultural ControlIt was found that wheat straw was propitious to broadleaf weeds and Cyperaceae weeds occurring but Poaceae weeds, and the amount of weeds was less affected by the amount of wheat straw. Wheat straw could delay the fastigium of the weeds occurring. Weeds were more serious under the wet management than conventional depth of water (2-3 cm) in paddy fields,4-5 cm water in paddy fields could control weeds effectively.3、 Chemical ControlThe susceptibility of weeds in mechanized rice to common herbicides was evaluated by whole-plant bioassay. Then the screening of the optimum mixtures was conducted by Gowing’s method and Sun Yunpei method. Research data showed that optimum mixtures were obtained as follows:the range of pyribenzoxim to cyhalofop-buty was 1:2-1:10; the range of pretilachlor to bispyribac-sodium was 15:1-30:1; the optimum mixtures of isoproturon and pretilachlor to halosulfuron-methyl were 34.5:14:1.5,29.5:16:1.5 or 24.5:18:1.5. The field trial results showed that the control effects of 10% pyribenzoxim-cyhalofop-butyl OF with dose of 1500,3000 ml/hm2 were over 80% to Echinochloa spp., L. chinensis, H. plantagineiformis, C. difformis, Eclipta prostrate L. Ludwigia prostrate Roxb. and Sesbania cannabina (Retz.) Pers. The control effects on weeds of 32% pretilachlor-bispyribac-sodium WP used before transplanting were better than after transplanting at the same dosage, but used before transplanting was not safe for rice. The annual weeds control effects of 32% pretilachlor bispyribac-sodium WP used after transplanting with dosages of 750,1200g/hm2 were over 80%.47% isoproturon-pretilachlor-Halosulfuron-methyl WP used before transplanting with dosages of 600,750,900,1500 g/hm2 got the control effects on annual weeds over 85%,and used after transplanting with dosages 750,900,1500g/hm2 got the same control effects.