Survey Of Weed Population In Hemp Land And Research Of Chemical Weed Control

System investigation of weed population and dynamic state was took in NingXiang County of Hunan Province.Then pre-emergence and post-emergence weed control test were applied on the basis of definition of dominant weed spicies.The results were as follows:(1) There were54species of weeds belong to22families,of which Gramineae,Compositae,Cyperaceae,Polygonaceae,Euphorbiaceae,Scrophulariaceae,Crucif erae,Leguminosae,Amaranthaceae,Caryophyllaceae,Convolvulaceae were the main families.Of the54weeds,there were separately10species of weeds belong to Gramineae and Compositae; RA value of Poa annual L., Alopecurus aequalis SoboL., Beckmannia syzigachne(Steud.)fern.,Digitaria sanguinalis(L.)Scop., Conyza Canadensis(L.)Cronq, Eclipta prostrate L., Cyperus iria L., Rumex crispus L. and Alternanthera philoxewides(mart.)Griseb were above10,which were the dominant species in Hemp field.(2) The Dynamic curve of weed in hemp field was a typical single-peak curve.The population of weeds increased with growth of hemp and reached the peak in the end of May.(3) For the pre-emergence test,control effect of Acetochlor, Metolachlor and Butachlor were separately90.25%,90.72%,90.02%15days after treatment, which were significantly higher than Prometryn and Butralin;Control effect of Acetochlor, S-metolachlor and Butachlor were still the best30days after treatment,although almost accordant decreace of control effect appeared. Control effect on fresh weight of Acetochlor, S-metolachlor and Butachlor were all above92%,which were also significantly higher than81.02%of Prometryn and78.60%of Butralin.(4) For the post-emergence test,control effect of Glyphosate was the best when applied separately,which reached98.68%. MCPA-Na was effective to broad-leaf weeds while inefficacious to Gramineae weeds. Clethodim, Haloxyfop-R-methyl, Quizalofop-p-ethyl and Metolachlor had obvious effect to Gramineae weeds while inefficacious to broad-leaf weeds.Control effect of MCPA-Na applied together with Clethodim and Haloxyfop-R-methyl significantly increased and reached separately92.74%and91.27%,which were much higher than applied with Quizalofop-p-ethyl and Metolachlor. (5) The best program of weed control was pre-emergence treatment with S-metolachlor plus post-emergence treatment with MCPA-Na and Haloxyfop-R-methyl,yields of fiber and kenels was respectively77.68kg/667m2and28.64kg/667m2,which increased respectively47.43%and45.09%. Good control effect and economic benefit could be gained on the basis of this program.