Chemical ripeners and different harvest periods in sugarcane in State of Paran, southern Brazil

The objective of this work was to evaluate the effects of control action (natural ripening, without ripeners) and of glyphosate, paraquat, fluazi-p-butil, ethephon, etyl-trinexapac, sulfometuron methyl and KNO3 on the number of stalks per area, diameter of the median third of stalks and productivity (tons of canesstalks per hectare), and brix, pol of the sugarcane and extractable sugar. It was used a randomized block design with four replicates in a sub-split plots. KNO3 contributes to improve agronomic quality by increasing productivity of stalks and the most favorable harvest period to the variable was from 60 to 120 days after ripener application (DAA). Etyl-trinexapac, sulfometuron methyl and KNO3 increased technological variables and the most adequate harvest period for ratoon sugar cane was 120 days after application (DAA) of ripeners and control, because they provided gains for variables ATR, Brix and PC in comparison to the respective initial reference times.   Key words: Plant regulators, Saccharum spp., technological quality.