The effect of weed management on banana (Musa AAA cv. Grande Name) parasitic nematodes was evaluated under Costa Rican field conditions with special reference to their spatial distribution and the damage caused to roots of different thickness classes and their relation to yield losses. Root samples were taken at plant harvest, from soil blocks at 0-30, 30-60 and 60-90 cm from the pseudostem, and at every 15 cm depth, from 0 to 120 cm. Weed management neither affected the nematode numbers nor their horizontal and vertical distribution and associated root damage. Differences in Radopholus similis (P < 0.0001), Helicotylenchus spp. (P = 0.0115) and total nematode populations (P < 0.0001) were found in roots of different thickness. The average populations in thick, thin and fine roots were for R. similis 270,666 (57%), 120,401 (25%) and 11,313 (2%); for Helicotylenchus spp. 36,094 (7%), 22 508 (5%) and 8,824 (2%); and total nematodes 390,425 (65%) 145,534 (31%) and 21,177 (4%), respectively. No linear correlations were found between bunch weight and the number and density of nematodes or with their damage. Even though, no statistical difference was found in bunch weight, the manual weed control plot yielded 1.4 kg heavier bunches, which might have important implications for sustainable agriculture. The implementation of weed control by hand chopping may improve the physical, chemical and biological soil properties and reduce soil erosion, temperature fluctuations, evaporation rate, and nutrient leaching, and increase water infiltration. As a consequence of the decrease in herbicide applications, soil and air pollution might be reduced. © 2005 Elsevier Ltd. All rights reserved.