Study On The Resistance Of Barnyard Grass To Quinclorac In Paddy Field Of The Middle And Lower Yangtse Valley In China

In this paper, the barnyard grass, a kind of worst weed in paddy field at the middle and lower Yangtze valley in China, was chosen as a main research object. The dormancy and its breaking methods of barnyard grass seeds, the susceptibility to different herbicides and the resistance to quinclorac of barnyard grass were studied systematically. Control of quinclorac-resistance barnyard grass was also studied in this paper. The results were as follows:The results of seed dormancy under different environmental conditions showed that the seeds of barnyard grass would get into dormancy after maturity, and the dormant period was different under different environmental conditions. The dormancy of barnyard grass seeds collected in July 2004 could be broken by buried in soil for 5 months, but they got into the second dormancy in the next July. The dormancy could also be broken by stored for one year under the room temperature. However, the seeds stored in refrigerator for one year were still dormancy.Mechanical damnification were advantageous in breaking dormancy of barnyard grass seeds. Cut at the top and cut at the end of the spikelets could broke dormancy of barnyard grass seeds, and the result of cut at the top excelled that cut at the end of the spikelets. Shelled spikelets only partly broken dormancy of barnyard grass seeds. The seeds were immersed in GA₃ with 1000 mg/L concentration or H₂SO₄ about 10-20 minutes could broke dormancy of barnyard grass seeds, but other disposal of GA₃ and H₂SO₄ could not broken dormancy of barnyard grass seeds. NAA, ethephon and ethanol could not broke dormancy under experimental concentration. However, on the base of shelled spilelets, GA₃, H₂SO₄, NAA, ethephon and ethanol could broken dormancy of barnyard grass seeds.The susceptibility of barnyard grass to 15 herbicides in different time were studied by filter paper method. The result showed the optimal time of barnyard grass to pyrazosulfuron-ethyl was 2 days. The best time of barnyard grass to penoxsulam, oxadiargyl, quinclorac, bispyribac-sodium, pyribenzoxim, pyriminobac-methyl and prometryn were 3 days. The most susceptibility time of barnyard grass to fentrazamide, oxaziclomefone, molinate and thiobencarb were 4 days. And the optimal time of barnyard grass to acetochlor, pretilachlor and butachlor were 5 days. Compared by agar method, filter paper method and pot-spraying method, the agar method was a most rapid and delicacy method in three kinds of methods to determine the susceptibility of barnyard grass to acetochlor, butachlor and quinclorac. Based on the EC₅₀, the susceptibility of 15 herbicides to barnyard grass by agar method is in the following order: oxaziclomefone, fentrazamide, acetochlor, oxadiargyl, butachlor＞pretilachlor, quinclorac, pyriminobac-methyl, penoxsulam, thiobencarb, bispyribac-sodium≥molinate, pyribenzoxim, pyrazosulfuron-ethyl＞prometryn.The resistant level of 43 barnyard grass collected from paddy fields in Zhejiang province, Jiangshu province, Anhui province, Jiangxi province and Hunan province were tested by agar method. The result showed the barnyard grass collected from Zhejiang Shaoxing in 2003 was the most susceptible barnyard grass to quinclorac, the EC₅₀ was 0.3268 mg/L. The barnyard grass collected from Zhejiang Taoyan(2003) and Zhejiang Tangxia(2003) were very high resistant to quinclorac, the resistance ratio were 718.48 and 695.84 respectively. The barnyard grass collected from Hunan Anxiang(2004) and Zhejiang Hangzhou(2003) were high resistant to quinclorac, the resistance ratio were 62.21 and 41.22. The resistant level of barnyard grass collected from Zhejiang Gaobu(2003) to quinclorac was low, the resistance ratio was 6.41. The other populations(38 populations) of barnyard grass were susceptible to quinclorac. So the resistant barnyard grass to quinclorac have been occurred in few paddy fields in Zhejiang province and Hunan province. The resistance of barnyard grass collected from Zhejiang Taoyan(2003), Zhejiang Tangxia(2003) and Zhejiang Hangzhou (2003) to quinclorac were also be demonstrated by single dose assay and pot-spraying method. In field trials, the result showed the barnyard grass in direct-seeding paddy field of Zhejiang Taoyan were resistant to quinclorac.The susceptibility of resistant and susceptible barnyard grass to 8 herbicides were studied by agar method. The results exhibited the EC₅₀ of quinclorac-resistant barnyard grass to acetochlor, butachlor, pretilachlor, penoxsulam, thiobencarb, fentrazamide, oxaziclomefone and oxadiargyl were near that of quincloracsusceptible, and indicated the susceptibility of quinclorac-resistant and quinclorac-susceptible barnyard grass to these herbicides were same. So these herbicides can use for control of quinclorac-resistant barnyard grass. Pretilachlor, bispyribac-sodium and penoxsulam gave adequate control of quinclorac-rcsistant barnyard grass in field trials.