Shoot elongation retardation owing to daminozide in Chrysanthemum: II. Modeling multiple applications

Abstract

A model for simulating the effect of an application of daminozide on shoot elongation of potted chrysanthemum ( Dendranthema × grandiflora (Ramat.) Kitamura) shoots was adapted to simulate the effect of multiple growth retardant applications using four different approaches. The resulting simulation model allowed testing of optimal strategies for timing daminozide concentrations as well as for comparison of predictions with observed shoot growth data. Of the four approaches tested, the two which performed best were (1) the elimination approach, where the residual effect from previous applications was discarded, (2) the residual-additive approach, where the residual effect from previous applications was incorporated by computing a theoretical daminozide concentration for the residual effect and adding this to the concentration of the new application. The elimination approach appeared to be more suitable for situations where multiple applications were spaced more than 7 days apart, while the residual-additive approach was better at closely spaced applications. These two approaches predicted that two spray applications of daminozide at concentrations of 0.25% a.i. would result in maximum shoot length reductions of 19% and 23%, respectively; 22% and 30% with three applications. The optimal application dates predicted with the elimination approach were Days 16 and 34 after pinching for two applications, and Days 11, 26, and 41 for three applications.