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A pot experiment was conducted at the Centre for Ecological Studies of the University of Port Harcourt, Rivers state, Nigeria to evaluate the efficacy of Primextra Gold herbicide in controlling weeds in melon and cucumber and to assess the extent of injury to the crops. The experiment was laid out in a Randomized Completely Design with four replications. Seven doses of the herbicide – 0.0kg a.i/pot (D0), 0.25 kg a.i/pot (D1), 0.5 kg a.i/pot (D2), 0.75 kg a.i/pot (D3), 1.0 kg a.i/pot (D4), 1.25 kg a.i/pot (D5) and 1.5 kg a.i/pot (D6) – were applied preemergence. The dry weight, height of plant, number of green leaves, weed control efficiency, weed persistence index, crop phytotoxicity rating, weed destruction rating were used to determine the herbicide efficacy and crop injury. Results show that the melon recovered from the injury caused by lower doses (D1, D2, D3) while higher doses (D4, D5, D6) caused stand loss and complete crop destruction. The maximum average height (72 cm/pot), maximum number of leaves per pot (20), second maximum average dry weight (2.98g/pot) was observed at 28 DAT in melon treated with D3. All the doses applied caused over 50% injury to the cucumber at all stages except at 7 DAT. The study also showed that Primextra Gold has a high Weed Control Efficiency (WCE %) and the Weed Persistence Index (WPI) of the weeds was low. Primextra Gold has a high weed destruction rating with the effect of the doses ranging from moderate to complete weed destruction.