Two field trials were conducted to determine the effect of low doses of glyphosate on tomato plant growth and marketable yield. The herbicide was applied to the foliage 1 day before transplanting. There was a rapid decline on tomato plant vigour and height as the herbicide dose reached 100mg/L. Marketable yield was also affected by sublethal herbicide doses, with a 41% yield decrease with 25mg/L of glyphosate. These results confirm that low glyphosate doses, which could be found in multi-purpose spraying equipment, might severely reduce tomato marketable yield.