Field studies were conducted in southwestern Mexico to determine the effect of three plastic mulch colours (black, white, and clear) on aphid populations, soil temperature, and on fruit yield of watermelon(Citrullus vulgarisSchard.). Aphids were counted on alternate days in traps placed on the mulched beds. Aphids were least numerous on the clear mulch and most numerous on the bare soil. Maximum soil temperatures under clear polyethylene reached 38.5°C and were 1.0, 4.5, and 4.2°C greater than those under white, black, and 10 cm deep unmulched soil, respectively. Total soluble solids of fruits were not modified by different coloured polyethylene. Fruit length was increased with clear and white plastic. Plants grown on clear plastic mulch produced higher marketable yields than those grown on bare soil. Other colours (black and white mulches) were intermediate in their effects on aphid populations, soil temperature, fruit weight, and yield response. Marketable yields of 48.3, 43.2, 38.3, and 22.8 t/ha were achieved under clear, black, white, and unmulched soil treatments respectively. Clear plastic mulch increased fruit weight by 2.94 kg and watermelon yield by 25.5 t/ha in comparison with unmulched soil. All plastic mulches increased fruit weight and total yield as compared with production on bare soil. By delaying aphid population increases, use of mulches may reduce the need for insecticides targeted for aphid control. In conclusion, coloured polyethylene mulch has an important effect, and clear plastic could be a practical management tool for the increase of watermelon production and enhancement of fruit quality under tropical conditions.