Traditional agronomic practices are often ineffective in preventing cotton (Gossypium hirsutum L.) yield losses due to the Columbia lance (CLN) nematode (Hoplolaimus columbus Sher), so control relies heavily on nematicides. Field experiments were conducted at two locations in 1996 and 1997 to document plant parameters affected by CLN and to determine yield losses in fields with low to moderate levels of CLN. Fumigation with 56 L ha-1 1,3-dichloropropene (1,3-D) resulted in a 77% reduction in CLN population densities at planting and a 21% increase in cotton yield across both locations and years. Plant mapping was conducted at first-bloom and at harvest to document the affects of CLN on cotton plant and yield parameters in order to explain yield losses induced by CLN. Yield losses were due to a 22% reduction in the number of harvestable (open) bolls in plants affected by CLN. Whole-plant mapping showed that second position harvestable boll retention of plants affected by CLN was 50% less than non-affected plants. Machine- and hand-picked (sequential dates prior to machine harvest) cotton yields resulted in delayed maturity of infected plants by 32% and 8% in 1996 and 1997, respectively. Understanding which plant parameters are affected by CLN can aid in the development of more productive management schemes that involve either cultivar selection, timing of defoliation, or planting dates and can further aid cotton breeders in the potential development of tolerant cultivars.