Herbicides as ripeners for sugarcane

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

Submitted to: Weed Science Society of America Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 10/2/2008
Publication Date: 2/1/2009
Citation: Richard Jr, E.P., Dalley, C.D., Viator, R.P. 2009. Herbicides as ripeners for sugarcane. Proceedings of Weed Science Society of America Meeting. 49:499.

Interpretive Summary:

Technical Abstract: At the start of the sugarcane harvest season in Louisiana, late-September or early-October, sucrose content in sugarcane is relatively low compared to late in the harvest season. In order for early-harvested sugarcane to be profitable, chemicals, primarily herbicides, have been evaluated for their efficacy in increasing sucrose content of sugarcane, i.e. ripening. The first sugarcane ripener registered for use in the U.S. was glyphosine, in 1975, which was replaced by glyphosate in 1980. Glyphosate is the only sugarcane ripener registered for use the U.S. Applied at 0.14 to 0.49 kg ae/ha, glyphosate inhibits growth of the apical meristem while synthesis and transport of sucrose to the maturing stalk internodes continues. Increases in sucrose content of as much as 30% can be measured in as few as 3 weeks with ripener applications of glyphosate being most effective while sugarcane is actively growing - conditions unfavorable for natural ripening. Glyphosate often reduces gross cane yields (Mg cane/ha), but sugar yields (kg sugar/ha) are increased because the increase in theoretically recoverable sugar (TRS; kg sugar/Mg cane) is enough to offset reductions in gross cane yields. Glyphosate use is restricted to the ratoon crops in Louisiana and Texas and only to the final ratoon crop in Florida. It is also applied to sugarcane in Hawaii where sugarcane is only harvested once from a planting after a 2-year growing season. Restrictions in use in Louisiana, Texas, and Florida are based on the concerns of potential injury to the subsequent ratoon crop from a misapplication. Applications can result in stunting and bleaching of shoots that emerge the following spring with the severity of the injury dependent on rate, treatment to harvest interval, and variety. The effects on the following year’s ratoon crop are usually transient and have been shown to impact yield only when additional stresses are encountered. A number of other herbicides have also been tested with limited success. The ACCase-inhibitor, fluazifop, has been tested in the U.S. and has been used commercially in other sugarcane producing countries. Several ALS-inhibitors, including imazapyr and nicosulfuron, as well as the gibberellin inhibitor trinexapac-ethyl, have also been tested. All of these have increased sucrose content while having a lesser impact on gross sugarcane yields and spring regrowth, but per hectare sugar yields have generally been lower than those obtained with standard glyphosate applications. The need for an alternative ripener to glyphosate may present itself if glyphosate-resistant sugarcane is adopted commercially. Glyphosate-resistant sugarcane would be a benefit primarily for controlling perennial grasses such as bermudagrass and johnsongrass as well as the annual itchgrass in Louisiana and the perennial napiergrass in Florida.