Autumn-planted sugarcane was seeded with itchgrass in early March to give 1 plant per 30.5 cm of row length (1.8 plants m−2). In three of four experiments, itchgrass was allowed to reseed and develop naturally in the second or third-yr ratoon crops. In the first-yr crop, itchgrass stands developed by May 15 and itchgrass was removed after 30, 60, or 180 d of interference. After 30 d interference, on about June 15, itchgrass biomass ranged from 200 to 2700 kg ha−1 in four experiments and reduction in sugar yield averaged 7%. After 60 d interference, on July 15, the biomass ranged from 1400 to 2900 kg ha−1 in two experiments and reduction in sugar yield averaged 17%. Itchgrass removed at harvest in November, after 180 d interference, reduced sugar yield by 19% in four experiments. Itchgrass infestations removed in the second-yr crop on May 1, June 1, and November 15 harvest reduced sugar yield in one experiment by 3, 11, and 72%, respectively, compared to a 2-yr weed-free control. Itchgrass interference reduced sugar yield primarily by reducing stalk population even though full-season interference increased sugar concentration of juice by 2 to 10%. These studies indicate that itchgrass must be removed from sugarcane well before June 15 (30 d of interference) under Louisiana growing conditions to prevent a rapid increase in itchgrass biomass and loss in sugar yield. However, sugarcane stands and yield recovered almost completely when maintained weed free in the second-yr crop following full-season itchgrass interference in the first-yr crop.