Use of herbicides and hand weeding are common practices for weed control in root and tuber crops throughout the Caribbean Basin. In Puerto Rico, herbicides ametryn and paraquat are registered for use in some root and tuber production, but no herbicides are registered for arracacha. Knowing the time at which weeds begin to interfere with arracacha will permit optimum timing for weed control practices. The objective of this study was to determine the effects of various duration periods of weed interference on arracacha plant dry weight, stand and fresh corm yield. The study was established using periods of interference as treatments. Weeds were allowed to grow for 0, 1, 3, 5, 7, 11, and 40 weeks after transplanting. Plant dry weight was reduced linearly at a rate of 32 g/m2 for each week of interference. Plants per hectare were reduced at a rate of 185 plants/ha for each week of interference. Analysis indicated a quadratic relationship between corm yield and lengths of weed interference.