028 Amaranthus dubius Interference in Sweetpotato

Amaranthus dubius is a common weed in sweetpotato production throughout the Caribbean Basin. A field study was conducted in the Agricultural Experiment Station at Juana Diaz, P.R., during 1998 to determine the effect of A. dubius interference in sweetpotato production under tropical conditions. Interference was evaluated by using a randomized complete-block design with four replications. Plots were four 6.1-m rows divided into two sections for yield and growth determinations. Intraspecific and interspecific interference was measured for both species. A. dubius was grown at 15 and 30 plants per meter of row. Plant dry weight and leaf area were determined at 3, 6, 9, 12, 15, and 18 weeks after planting (WAP). Sweetpotato yield was determined at 29 WAP. A. dubius growing alone reached a maximum leaf area index (LAI) of 8.5 at 12 WAP. Sweetpotato, however, did not attain maximum LAI. When grown with A. dubius , sweetpotato biomass was reduced at 15 WAP. This reduction was 62% and 66% for 15 and 30 A. dubius plants per meter of row, respectively. Sweetpotato yield in weed-free plots was equivalent to 9232 kg/ha. Yield reduction was 96% for 15 A. dubius per meter of row and 100% for 30 plants.