Late-season glyphosate ripener application coupled with post-harvest residue retention impacts subsequent ratoon yields

Authors: Viator, Ryan; Dalley, Caleb; Richard Jr, Edward

Submitted to: International Sugar Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2011
Publication Date: 5/1/2011
Citation: Viator, R.P., Dalley, C.D., Richard Jr, E.P. 2011. Late-season glyphosate ripener application coupled with post-harvest residue retention impacts subsequent ratoon yields. International Sugar Journal. 113(1349):374-380.

Interpretive Summary: The application of low dosages of the herbicide glyphosate to enhance sugar accumulation (ripening) in sugarcane that will be harvested in the last third of Louisiana’s sugarcane harvest is sometimes conducted, even while its use may have little or no economic value and has potential to cause injury to the subsequent ratoon crop. Glyphosate was applied to four varieties to determine increases in sugar yields, its residual herbicidal effects on next year’s crop (ratoon), and its interactions with the blanket of leafy trash (residue) generated during green-cane harvesting. Regardless of variety, a late-season glyphosate ripener application offered no sugar yield advantage in first ratoon. In the subsequent second ratoon, the residual effect of glyphosate when post-harvest residue was fully retained reduced sugar yields by 13% relative to the no glyphosate control. It is recommended that Louisiana producers not apply glyphosate to ripen cane where post-harvest residue cannot be removed. Moreover late-season glyphosate ripener applications are also not recommended due to a lack of response.

Technical Abstract: The application of a low dose of glyphosate as a sugarcane ripener to sugarcane that will be harvested in the last third of Louisiana’s sugarcane harvest is sometimes conducted, even while its use may have little or no economic value and has potential to cause injury to the subsequent ratoon crop. The objectives of this experiment were to determine: 1) if late-season (Nov. 1) glyphosate ripener application increases sucrose yield in the four common commercial sugarcane varieties grown in Louisiana, 2) varietal differences in susceptibility to injury from residual glyphosate in successive ratoon crops, and 3) if the stress of residual glyphosate on the subsequent ratoon crop is compounded by the presence of post-harvest residue. Glyphosate was applied on Nov. 1 (0.21 kg ai ha-1) to the first-ratoon crop. Two weeks after the first ratoon was harvested, the blanket of crop residue was either allowed to remain or completely removed by burning. Regardless of variety, late-season ripener application offered no increase in sucrose yield in first ratoon, and residual effects of glyphosate in the subsequent second-ratoon crop yield were not variety specific. Residual effect of glyphosate when post-harvest residue was not removed reduced sucrose yields by 13% relative to the non-treated control. Sucrose yield in the second-ratoon crop was not reduced when glyphosate was applied and residue was removed. When treated with glyphosate the previous year, residue retention reduced stalk population and photosynthesis in the second-ratoon crop compared to when residue was removed. It is recommended that Louisiana producers not apply glyphosate as a ripener where post-harvest residue cannot be removed prior to the start of the next production year of a crop cycle. Moreover late-season glyphosate ripener applications are also not recommended due to a lack of response by sugarcane coupled with the potential of residual injury effects caused by translocation of glyphosate into the crown, especially if post-harvest residue cannot be removed prior to the emergence of the subsequent ratoon crop.