Critical Growth Stages for 2,4-d Phytotoxicity to Sugarcane in South Africa

Field trials were used to investigate the phytotoxicity of foliar sprays of 2,4-D amine to sugarcane. Yield losses of variety NCo 376 resulted from band sprays when 3,3 kg ae/ha was sprayed onto plant or ratoon cane which had unfurled three or more leaves per shoot. The greater the foliar development of the crop at the time of spraying, the greater was the resulting crop loss. At similar stages of development plant crops were affected slightly more than ratoons. The addition of a surfactant considerably increased crop loss. Directed sprays which minimised foliar contact caused no yield loss, even at susceptible growth stages, except when excessive doses (20 ,kg ae/ha) were applied. Differential varietal tolerance was recorded, NCo 376 being highly susceptible, whereas both NCo 382 and NCo 310 were tolerant. No residual effects were apparent in subsequent ratoons. Some field practices are recommended that reduce the incidence of 2,4-D injury.