The increasing prolonged droughts and rainfall variability are significant factors contributing to increasing water scarcity, limiting vegetable yields in addition to weeds. Water scarcity is a global concern, negatively impacting food security and rural livelihoods in developing regions, particularly Sub-Saharan Africa, where livelihoods chiefly depend on rainfed agriculture. Mulching is a soil conservation approach that controls surface evaporation (E), a significant component of evapotranspiration (ET), which influences water use and vegetable growth. The influence of poly-mulch on weed management and water use efficiency was evaluated in a field experiment conducted between May and September 2018 in open greenhouse conditions at Tokyo University of Agriculture, Japan, on a plot of 30 cm² with drip irrigation and tomato cultivation. Three irrigation regimes, 2, 3 and 4 mm/day, defined from evaporation, were applied on black poly-mulch and no-mulch sections. Data on soil conditions—soil pressure head and soil temperature, as well as climatic variables, including solar radiation and temperature—were collected during the tomato cultivation period, while yield components—yield, water productivity, and sugar content—were determined after harvest. The results of a two-way ANOVA showed that poly-mulching with all irrigation regimes reduced the weed biomass and improved yields and water use efficiency compared to no-mulch conditions. Applying poly-mulches with 3 and 4 mm/day had a 5% significant effect on tomato yield compared to no mulch. Poly-mulching is vital for weed management and the application of irrigation regimes; 2-4 mm/day based on evaporation improves water use efficiency for tomato cultivation.