effect of herbicides and crop residue on integrated weed control in potato

crop residue is a non-chemical method of weed control in agricultural sustainable systems. this research was conducted at the alarogh site of ardabilto evaluate the effect of integrated use of mulch and herbicide on weed emergence and growth in potato in 2007. treatments were four levels herbicide including: (1) paraquat [n,n'-dimethyl-4,4'-bipyridinium dichloride] herbicide as pre-planting, (2) metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5-one] herbicide as pre-emergence, (3) paraquat as pre-planting plus metribuzin as pre-emergence and (4) without herbicide (control) as main plots, and four levels crop mulch including: (1) wheat residue, (2) barley residue, (3) canola residue and (4) without mulch as subplots. results showed that metribuzin application reduced weed density at the both stages (flowering and pre-harvesting) two times. crop residue on the soil surface completely suppressed winter and early spring weed emergence and growth, but did not suppress on lately spring weed. in plots that was applied metribuzin herbicide plus crop residue redroot (amaranthus retroflexus) and lambsquarters (chenopodium album) density was reduced to lower than 3 plant m-2, and purslane (purtolace olerace) density declined to lower than 8 plant m-2. these results show that: 1) crop residue can suppress winter weed growth specially to flowering stage of potato, 2) the effect of crop residue on soil surface decline after 4 to 6 weeks and weeds which emerged after need control by either practice.