Response of Sugarcane (Saccharumsp.) Cultivars to Preemergence Herbicides

Abstract

The potential diversity in tolerance of eight commercial sugarcane cultivars to metribuzin, terbacil, and hexazinone was investigated. Herbicides were applied preemergence in the fall after planting and postemergence to the crop in the spring each year over the 3-yr crop cycle. Reductions in shoot counts and heights were not observed with any of the herbicide treatments in the fall following planting. Cultivar differences in growth and yield responses were obtained, particularly in the plant cane year of the 3-yr crop cycle. Metribuzin was the least phytotoxic and hexazinone the most phytotoxic. Reductions in sugar yields (kg/ha) were attributed to reductions in stalk populations and, to a lesser extent, to reductions in stalk height and sugar (sucrose) content. Cultivars sensitive to hexazinone either were equally sensitive to terbacil or were less sensitive to terbacil. Terminal fluorescence (FT)3measurements indicated that photosynthesis following postemergence applications of terbacil and hexazinone was no longer inhibited 5 weeks after treatment in the tolerant cultivars, CP 70–321 and CP 74–383, but continued to be reduced in the cultivars showing sensitivity, CP 65–357 and CP 48–103. The order of cultivar tolerance to hexazinone and terbacil from least tolerant to most tolerant is CP 48–103 < CP 65–357 ≤ CP 72–370 < CP 70–321 = CP 70–330 < CP 72–356 = CP 73–351 = CP 74–383.