Evaluation of Organic Alternatives for Weed Management in Pulasan (Nephelium ramboutan-ake)

In Puerto Rico, most fruit crop growers use post-emergence synthetic herbicides as a major component of their weed management programs. Organic growers are not allowed to use synthetic herbicides, hence there is a need to develop alternative weed management strategies for current and prospective organic fruit growers. Pulasan (Nephelium ramboutan-ake, Sapindaceae), a relatively new crop in Puerto Rico with high economic potential, was used as a model to evaluate practices for weed control acceptable to organic systems as alternative to synthetic herbicides. Research was conducted in 2013 in a commercial orchard in the mountains east of Mayaguez, Puerto Rico. The treatments were (1) living ground cover of Mucuna pruriens under the tree, (2) living ground cover of Aranchis pintoi under the tree, (3) ground cover with sacks of jute (Corchorus olitorius) under the tree, (4) using a hand-held trimmer on weeds up to 30-cm tall, (5) a 20% organic acetic acid formulation sprayed on weeds up to 30-cm tall, (6) a 10% organic limonene formulation sprayed on weeds up to 30-cm tall, and, as the check treatment used by growers (7) a 1% solution of glyphosate sprayed on weeds up to 30-cm tall. Sorghum halepense was the most abundant weed during the experiment. By 60 days after implementing the treatments, weed dry weight accumulation above-ground was statistically the same in plot managed with acetic acid, trimmer, ground cover of  A. pintoi, ground cover of M. pruriens, or glyphosate. Plots with jute ground cover accumulated significantly less (approximately 50%) weed dry weight above-ground than plots where glyphosate was used, while plots sprayed with limonene accumulated significantly more weed dry weight above-ground than glyphosate-treated plots and approximately three times as much weed dry weight as jute-covered plots. These results indicate that jute ground cover may be a more efficacious and environmentally friendly alternative to glyphosate in pulasan orchards, and that trimming, postmergence application of acetic acid, and living ground covers of M. pruriens and A. pintoi may be as efficacious as glyphosate for weed suppresion.