AbstractDowpon, Roundup, Gramoxone and mixtures of Karmex with Dowpon or Gramoxone applied with different frequency were evaluated for weed control in young sun-grown coffee trees at Adjuntas Agricultural Experiment Substation, located at lat. 18° N. and long. 66°48' W., and at an elevation of 588 m. Gramoxone (0.95 L/ha) applied at one- or two-month intervals provided excellent weed control. Dowpon at 5.65 and 11.30 kg/ha was equally effective on grasses but ineffective on broadleaves. Roundup (1.90 L/ha) provided good weed control without producing detrimental effects on tree growth and yield. The addition of Karmex to the Gramoxone or Dowpon solution to increase effectiveness in control is questionable. Tree mortality was higher and coffee yield lower when Karmex was added to the solution than when either Gramoxone or Dowpon was used alone. When Dowpon was applied at a rate of 11.30 kg/ha, coffee production was significantly higher than production of the remaining treatments, except for that of the application of 5.65 kg/ha of Dowpon at 12-week interval. The production of the latter plots was significantly higher than that of plots in which Karmex (2.26 kg/ha) was added to the Dowpon (5.65 kg/ha) or the Gramoxone solution (0.95 L/ha) and applied each at 12-week intervals. Coffee yield when the weeds were controlled by Roundup (1.90 L/ha) or Gramoxone (0.95 L/ha) was significantly higher than that when Karmex (2.26 kg/ha) was added to the Gramoxone solution and applied every 12 weeks.
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