Beans (Phas eolus vuZgaris Linnaeus, 1 753) pest management through weeds background associated with varietal resista nce During the first dry season of 1978 (January-March) was carried out at the Centro Internacional de Agr i c ult u r a Tropical -CIAT, Colombia , a study of weeds background effects associa t ed with varietal resistance in beans (Phas eoZus vuZgaris Linnaeus , 1753) , pest popula ti on, vírus inci dence and yield . l t was o b served that t he background soi l weeds Leptochloa fiZi formis (LAl1 .) BEAUV., and chac weeds ki ll ed by herbicide have had some effects on adults popu laci on and nymph of Empoasca kraemeri ROSS & MOORE , 1957 and that th e presence of weed s killed by he rbi c ide decrease vírus in c id e n ce .Also , it was found that the g r ea test damages caus e d by larval and the highes t populati o n of Chry some lidae adu lt s t ook place in the plots where weed seeds have been p r ev i ous l y sowed .The variety ' Cal i ma ', suscetiple to insects and d is eases, yielded less tha n ' Pl4 ' varie ty .Among t he treatment s where weed seeds have been previously sowed , the variety ' Ca lima ' yielded more when i nsect i c ide was applied, followed by treatment where weeds were kil l ed by herbicide; which yield was signifi c antly different to the contro l .' Pl4 ' responded t o the tr e atme nt s and yielded more than ' Calima' .Weeds killed by h erbi cid e treatment was effective ; it yielded 21% l es s than the compl e t e pro t ec t ion treatmen t .Yield analys is showed that occurred competition betwee n weeds and beans, and that weeds effect decreas ed yie ld of bean in 25%. INTRODUCCIÔN