|Richard Jr, Edward|
Submitted to: American Society of Sugar Cane Technologists
Publication Type: Abstract Only
Publication Acceptance Date: April 6, 2011
Publication Date: June 10, 2011
Citation: Dalley, C.D., Richard Jr, E.P. 2011. Seasonal timing of glyphosate ripener application affects sugarcane’s response in Louisiana [abstract]. Journal of the American Society of Sugar Cane Technologists. 31:69. Available: http://assct.org Technical Abstract: Glyphosate is applied as a ripener to ratoon sugarcane in Louisiana to increase theoretically recoverable sugar (TRS) in harvested sugarcane. While glyphosate is applied as a ripener throughout the harvest season, recommendations for these applications have been based primarily on the response of sugarcane to ripener applied early in the harvest season (August or September). In order to improve recommendations for these ripener applications, experiments were conducted in 2006, 2007, and 2009 to measure the response of sugarcane to ripener applications throughout the harvest season. Beginning in mid-August, glyphosate (0.2 kg/ha) was applied to a commercial sugarcane field four times during the harvest season, with applications at four-week intervals and were compared to non-treated sugarcane. Plot size was two 1.8m wide rows and 15 m long with six replications of each treatment and were arranged in a split-plot design. Sugarcane ‘HoCP 96-540’ was hand-harvested at four, five, six, and seven weeks after treatment (WAT). Fifteen consecutive stalks were cut from a random location within each plot and weighed to determine average stalk weight. Five of these stalks were randomly selected to determine whole stalk response to ripener application. The remaining 10 stalks were divided into thirds to measure response based on location within stalk. These divisions are termed bottom (the four basal nodes of each stalk), middle (the next four internodes), and top (the remaining internodes). At 7 WAT, plots were harvested using a chopper harvester to determine plot weights and stalk piece (billet) samples were collected from each plot. All samples were processed using the core/press method, with TRS being determined from Brix, Pol, and fiber measurements. Averaged for the three years of this study, glyphosate applied in mid-August increased whole-stalk TRS by 21% compared to the non-treated control. Glyphosate applied four weeks later (early-September) increased whole-stalk TRS by 11%. Applications made another four weeks later (early-October) increased TRS 8%. There was no increase in TRS when the final glyphosate application was made in either late-October or early-November. The greatest increases in TRS were observed in the top of the stalk with increases as much as 50% when glyphosate was applied in mid-August. While there was no significant increase in whole-stalk TRS for the last glyphosate application, there was a 3% increase in TRS in the tops of these stalks. Even while the greatest increases in TRS were seen in the top portion of the sugarcane stalk, increases were also observed in the middle and bottom of the stalk where internodes were generally considered to be mature. For applications made in mid-August, TRS increased 13 and 19%, respectively, for the bottom and middle stalk portions. Treatment to harvest intervals did not affect the percent increase in TRS appreciably. Glyphosate applied in mid-August increased TRS 20, 24, 20, and 21%, respectively, for harvests at 4, 5, 6, and 7 WAT. Stalk weights were reduced by 8 and 9%, respectively, at the 6 and 7 WAT harvest dates when glyphosate was applied in mid-August, but not at earlier harvest dates. When glyphosate was applied in early-September, stalk weight was reduced 11% only at the 7 WAT harvest. Stalk weight was not reduced at the later glyphosate application dates. Gross cane yields at 7 WAT were reduced 7 and 12%, respectively, when glyphosate was applied in mid-August or early-September, but yield was not reduced with later applications. Glyphosate increased sugar yields 13% when applied in mid-August and 8% when applied in early-October, but neither increased nor decreased sugar yields when applied in either early-September of early-November. For applications made in early-September, all gains in TRS were offset by losses in tonnage. This study showed that glyphosate can be used to effectively increase TRS levels in harvested sugarcane through three-quarters of the harvest season. While the increase in TRS was greatest early in the harvest season, applications made in the middle of the season also increased TRS. As sugarcane is still actively growing in August and September, and the percent increase in TRS is similar when harvested at 4 or 7 WAT, perhaps utilizing a treatment to harvest interval of 4 or 5 weeks would further increase sugar yields for cane harvested in the first third of the harvest season. This would allow the sugarcane to increase in tonnage and maturation prior to glyphosate application. With no response to glyphosate applications made in late-October or early-November to cane scheduled for harvest in the latter third of the harvest season, it would not be recommended to continue applications beyond the middle of October.