Strategies to replace or complement hand weeding in herbicide-free systems, such as solarization and mulching, need thorough investigation in tropical environments. The influence of pre-plant solarization and crop-mulching on weed growth were tested in organically-grown onion crops in two field-plot trials in St. Andrew, Jamaica. Solarization was conducted during the 'dry winter' season using clear or black plastic for varied durations. Onion crops were transplanted at the end of solarization, with mulches of grass or black-plastic included in combination with solarization or as individual treatments in the second trial. Solarization for only 2 weeks was insufficient, but durations of 4 or 6 weeks with clear plastic reduced weed growth for 5 weeks (by 56% compared to the non-weeded control); a minimum of 6 weeks' solarization using black plastic was needed for similar effect. Mulching with grass after solarization gave greater reductions in weed cover over the first 7 weeks than solarization alone, but under rainy conditions the mulch decomposed quickly, losing its ability to suppress weed growth. The grass needed replacing to maintain a thick enough layer of mulch for continued weed suppression. Black-plastic mulching provided long-lasting and effective weed control, which was not significantly increased by preceding solarization. The treatments altered weed composition, variably changing species abundance. Grass weed densities were lowest after clearplastic solarization; nutgrass was reduced by black-plastic solarization of at least six weeks' duration. Both solarization and mulching showed potential for weed management in herbicide-free, tropical vegetable production, being equivalent to one or more handweeding operations. Strategies using combinations of the two methods, under different climatic conditions or seasons, especially warrant further investigation.


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