Influence of Nonoptimal Ripener Applications and Postharvest Residue Retention on Sugarcane Second Ratoon Yields

Retention of sugarcane (interspecific hybrids of Saccharum spp.) postharvest residue and certain glyphosate ripener application regimes may independently reduce yields of the subsequent ratoon crop in wet climates. The objective of this experiment was to determine the effects of ripener application and ripener treatment to harvest intervals (THI) on yields of the treated first ratoon, and the combined effects of these treatments and postharvest residue retention on the subsequent second ratoon. Whole plots consisted of either a nontreated control or 0.21 kg a.e. ha-1 glyphosate applied to the first ratoon of cultivar LCP 85-384. Split-plots consisted of THI of 40, 50, and 60 d for all plots. Split-split plot treatments consisted of partial removal of postharvest residue or complete retention for second ratoon. Averaged across all THIs for the first ratoon, glyphosate increased sucrose yield by 300 kg ha-1 compared with the control. The 60 d THI reduced second ratoon cane and sucrose yields by 5.4 Mg ha-1 and 900 kg ha-1, respectively, compared with the means of the 40 and 50 THI and sucrose yields by 300 kg ha-1 compared with the control. Full residue retention reduced second ratoon cane and sucrose yield by 2.3 Mg ha-1 and 300 kg ha-1, respectively, compared with partial removal. Residue retention and glyphosate application were not negatively synergistic. Producers should remove postharvest residue from the row top and harvest ripener-treated cane at a THI of 40 to 50 d to maximize sucrose yields in the first ratoon while also preventing yield losses in the subsequent second ratoon.