Effect of synthetic auxin herbicides applied during sugarcane grand growth on starch accumulation and color

Authors: Spaunhorst, Douglas; TRIPLETT, ALEX - Audubon Sugar Institute; ST. CYR, ELDWIN - Audubon Sugar Institute; EGGLESTON, GILLIAN - Audubon Sugar Institute

Submitted to: Sugar Tech
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: Sugarcane is grown on approximately 450,000 acres in Louisiana. Morningglory spp. and other vining broadleaf weeds infest sugarcane fields and herbicides are applied to control these weeds before overtaking the crop canopy and reducing harvesting efficiency. Sugarcane vegetation exposed to herbicides during rapid crop growth, often from June through September, may influence starch and colorant accumulation in some cultivars and reduce processing efficiency at sugar factories and refineries. In this study, three commercial field sugarcane cultivars were treated with 2,4-D, dicamba, or a mixture of 2,4-D plus dicamba. Visible crop injury was not observed following application of the three herbicide treatments. Treatments with dicamba or 2,4-D did not increase or decrease total or insoluble starch in extracted sugarcane juice. However, when compared to the untreated control, 16 to 25% more soluble starch was present in juice from L 01-299, HoCP 96-540, and HoCP 04-838 sugarcane that were exposed, in July, to dicamba and the mixture of dicamba plus 2,4-D. This is most likely related to natural diastase activity in the sugarcane and further investigation is now warranted. Late-season applied herbicides did not significantly influence color measured at pH 4.0, 7.0, 8.5, or 9.0; however, pH by cultivar interactions influenced color at pH 7.0 or greater, i.e., phenolic colorants. Overall, this study documented dicamba and 2,4-D plus dicamba were beneficial in controlling morningglory spp. and pose no threat to processing difficulties often caused by excessive starch and colorants in processing streams at both the factory and refinery.

Technical Abstract: Morningglory spp. and other vining weeds infest Louisiana sugarcane fields and synthetic auxin herbicides are applied to control such weeds. Sugarcane exposed to herbicides during the critical growth period (grand growth) may influence starch and colorant accumulation in some cultivars and reduce processing efficiency. In this study, field sugarcane composed of three commercial cultivars, were treated with 2,4-D, dicamba, or a premix of 2,4-D plus dicamba synthetic auxin herbicides to prevent yield losses and maximize harvesting efficiency. No visible abnormalities in sugarcane growth were observed following application of the three herbicide treatments. Treatments with dicamba or 2,4-D did not increase or decrease total or insoluble starch in extracted sugarcane juice. However, when compared to the untreated control, 16 to 25% more soluble starch was present in juice from L 01- 299, HoCP 96-540, and HoCP 04-838 sugarcane that were exposed, in July, to dicamba and the pre-mix formulation of dicamba plus 2,4-D. This is most likely related to natural diastase activity in the sugarcane and further investigation is now warranted. Late season applied synthetic auxin herbicides did not significantly influence color measured at pH 4.0, 7.0, 8.5, or 9.0; however, pH by cultivar interactions influenced color at pH 7.0 or greater, i.e., phenolic colorants. Overall, this study documented that the synthetic auxin herbicides dicamba and 2,4-D plus dicamba were beneficial in controlling morningglory spp. and pose no threat to processing difficulties often caused by excessive starch and colorants in processing streams at both the factory and refinery.