Factors Affecting the Efficacy of Dikegulac Sodium on Poinsettias

A better understanding of the variables in the use dikegulac sodium to promote branching of floriculture crops is needed.  Four experiments were conducted with non-pinched poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch).  Time of application is given as days after planting (DAP) rooted cuttings.  Dikegulac sodium (Augeo) was sprayed using a volume of 300 mL·m^-2, except where indicated.  A surfactant was not used.  Efficacy was determined as the difference in the heights of the tallest shoot (usually the main stem) and the second tallest shoot (usually a lateral branch).  More uniformly branched plants have less difference in these shoots.  For three cultivars sprayed 7 DAP with dikegulac sodium at concentrations of 0 to 1,600 mg·L^-1, response increased with concentration in all cultivars; however, efficacy was greater in ‘Prestige Red’ and ‘Early Prestige Red’ than in ‘Jubilee Red’.  Importance of spray volume was evaluated with ‘Early Prestige Red’ using volumes of 100 to 400 mL·m^-2.  For both 800- and 1,200-mg·L^-1 concentrations, increased spray volumes increased the efficacy of the dikegulac sodium sprays.  In a “wash off” experiment, dikegulac sodium was applied 10 DAP to ‘Prestige Red’ (1,200 mg·L^-1) and ‘Early Prestige Red’ (800 mg·L^-1), and then plants received overhead irrigation for 10 seconds.  The timing of the irrigation event was from 1 minute to 24 hours after the spray.  The control treatment was plants that were sprayed but not washed.  The results for the two cultivars were similar.  Overhead irrigation up to 1 hour after the spray greatly reduced efficacy, and irrigation at 4 hours reduced efficacy by about 50%.  Plants irrigated 24 hours after the dikegulac sodium application were only slightly different from the control plants.  In the fourth experiment, dikegulac sodium was applied to ‘Prestige Red’ using concentrations of 800 or 1,200 mg·L^-1. The application was made either 4, 7, or 10 DAP.  This experiment included an additional set of plants that were not sprayed and another set that were pinched.  All plants sprayed with dikegulac sodium were better than the non-pinched plants that were not sprayed.  Efficacy was greater at the higher concentration for each application time.  Efficacy at 7 and 10 DAP was similar and better than at 4 DAP.  Plants in the 1200-mg treatments at 7 or 10 DAP were similar to the pinched plants.