Sugarcane Flower-Control Studies With Paraquat, Gibberellic Acid, and Sodium Meta-Silicate

Abstract

Sugarcane flower control studies were conducted with Paraquat, gibberellic acid (GA) and sodium meta-silicate (Si) applied as foliar sprays just prior to the period of floral initiation. The test clone, C.P. 52-43, blooms heavily in southern Puerto Rico and initiates flower primordia about September 10. The primary objective was to determine whether flowering could be prevented by physiologically removing the apical meristem, with a growth stimulant such as GA, rather than by destruction of the green top, as by treatment with a desiccant such as Paraquat. Secondary objectives included comparisons of growth and sugar responses to GA and Paraquat, and to determine whether Si, believed to act as a buffer against physiological extremes, possessed anti-flowering activity. Two experiments were conducted simultaneously in a field of 7-months old, first-ratoon cane at Central Mercedita, Ponce. Each experiment was given identical spray applications of GA and Si; in addition, one experiment received Paraquat superimposed over all plots shortly after the GA and Si applications were complete. Aqueous GA, 0.01 percent active material, was applied with knapsack sprayers to 1/1000-acre plots in volumes equal to 300 gallons per acre. Si was similarly applied at the level of 500 p.p.m. Treatments also included GA and Si combined in one solution. Paraquat was applied by aircraft at the rate of 0.5 pint per acre in 8 gallons of water per acre. GA and Si treatments were given on August 22 and repeated on August 29. Paraquat was applied once on September 1. The following results were obtained: 1. Flower counts taken on December 27 showed that GA given alone was the most effective treatment, reducing flowering rates to 0.02 percent. Paraquat reduced flowering to about one-third of control levels. Si had no effect by itself, but reduced the effectiveness of GA when the two agents were combined. 2. Total green weights, stalk weights, and internode lengths were increased by GA. Each parameter was decreased by Paraquat. Si given alone appeared to increase total green weight and stalk weight but the responses were not statistically significant. The primary effect of Si in combination with GA and Paraquat was to reduce the degree of growth stimulation by the hormone, and to lessen the growth suppression by the desiccant. 3. Sugar production was increased by GA and decreased by Paraquat. Paraquat also lessened the degree and duration of positive GA effects. Si had little effect on sugar as a lone entity but produced a buffering effect against relative sugar extremes as it did for growth extremes. 4. Early Paraquat injury to leaves, and hence to sugar-forming mechanisms, appeared to be more than compensated after about 2 months. Tonnage losses due to the foliar injury appeared to be permanent. 5. GA growth stimulation was followed by a reversion to less than normal growth. This growth reversion detracted from the total growth increases that otherwise might have been achieved. It was proposed that growth decline could be lessened with Si given as a delayed or follow-up treatment after GA. 6. Present evidence is consistent with the view that sugarcane flowering can be prevented more effectively by stimulating the apical meristem, at the critical period of flower initiation, than by destroying foliate essential for maximum growth and sugar production.