|Richard Jr, Edward|
Submitted to: American Society of Sugar Cane Technologists
Publication Type: Abstract Only
Publication Acceptance Date: 6/20/2006
Publication Date: 6/20/2006
Citation: Richard Jr., E.P., Dalley, C.D., Viator, R.P. 2006. Ripener influences on sugarcane yield in Louisiana [abstract]. Journal of the American Society of Sugar Cane Technologists. 26:54. Available: http:www.assct.org/journal/journal.htm Interpretive Summary:
Technical Abstract: The combination of Louisiana’s climate-induced short growing season with the need to begin the harvest season earlier to makeup for shortages in milling capacity, and an overall need to increase production efficiencies at both the grower and processor level is forcing the industry to rely heavily on low rates of the herbicide (glyphosate) to enhance the natural ripening of the crop. Studies were conducted to evaluate: the ripening response of Louisiana’s leading variety, LCP 85-384, to various formulations and rates of glyphosate applied to ratoon crops; the application of experimental ripeners to the ratoon crop and over the ratoon crops of a crop cycle; and the response of the newer varieties released to the Louisiana industry to glyphosate in comparison to LCP 85-384. In the first study, the Polado L®, Roundup Weathermax® and Touchdown iQ® formulations of glyphosate were applied on 7 September 2004 and 18 August 2005 to first-ratoon crops at acid equivalent (ae) rates of 0.125, 0.187, and 0.25 lbs ae/A with stalks being harvested at 4, 5, and 6 weeks after treatment (WAT) for juice analysis and yield estimations. Formulation by rate interactions were not significant suggesting that the formulations performed similarly in increasing the theoretically recoverable sugar (TRS) levels and sugar yields of the harvested crop when compared to the non-treated check. The TRS levels increased as the rate of glyphosate applied increased; however, the response at the 0.25 lbs/A rate was generally equivalent to the 0.187 lbs/A rate and greater than the 0.125 lbs/A rate. In a second study, the response of annual (late-August/early-September) applications of glyphosate (Polado L®) at 0.187 lbs/A and three alternative ripeners, imazapyr (Arsenal®) at 0.094 lbs active ingredient (ai)/A, nicosulfuron (Accent®) at 0.042 lbs ai/A, and trinexapac-ethyl (Palisade®) at 0.27 lbs ai/A to ratoon crops were compared. All of the treatments increased TRS levels 6 and 7 WAT of the treated crop when compared to the non-treated check. However, yearly increases in sugar levels with glyphosate at the standard rate of 0.187 lbs/A did not increase the total sugar yields for the three ratoon crops (12,300 lbs/A) when compared to the non-treated check (12,100 lbs/A). The reduction in the total sugar yield following repeated applications of glyphosate was attributed to a reduction in gross cane yield and not to a reduction in April shoot counts. Imazapyr, nicosulfuron, and trinexapac-ethyl did not reduce cane tonnages. As a result, total sugar yields for the ratoon crops were 1,200 to 2,000 lbs/A higher than the glyphosate standard. In a third study, glyphosate (Polado®) applied at 0.187 lb/A with a nonionic surfactant at 0.5% by volume consistently increased TRS levels 6 WAT in second-ratoon crops of LCP 85-384, HoCP 85-845, HoCP 91-555, HoCP 96-540, and L 99-233 to similar percentages when compared to the no glyphosate treatment. The standard rate of glyphosate did not increase TRS levels 6 WAT for L 97-128, suggesting that a longer treatment to harvest interval or higher rates of glyphosate may be needed to elicit a ripening response from this variety which has been characterized as the earliest maturing variety currently being grown in Louisiana. The seasonal application of glyphosate, regardless of formulation, at 0.187 lbs/A to enhance ripening continues to show positive benefits. Yield decline is a characteristic of all of the varieties released prior to LCP 85-384, and LCP 85-384 has in the last few years been showing similar signs of yield decline. Our results suggest that the repeated application of glyphosate to LCP 85-384 over the entire crop cycle may be exacerbating this problem as gross cane yields in subsequent ratoon crops of LCP 85-384 appear to be declining at a faster rate when glyphosate is applied annually over the crop cycle.