Silicate Sprays as Effective as Calcium Sprays at Suppressing Bract Necrosis in Poinsettia

in HortScience

Bract necrosis (BN) first appears at anthesis, and symptoms become more numerous and severe with time. Previously, we reported that 3.6 mm sodium silicate (Na2SiO3) sprays, applied during bract development, were as effective as 10 mm CaCl2 sprays at suppressing BN on `Supjibi' and `Angelika White', but only for several weeks after initial anthesis. While applying Na2SiO3 during bract development dramatically suppressed BN (7.2% of bracts with BN 46 days after anthesis vs. 33.4% for untreated plants), applying Na2SiO3 after anthesis is ineffective (35.7% BN). In 1995, suppression of BN was evaluated on `Supjibi' plants sprayed with similar concentrations (2 or 4 mm) of Na2SiO3 and CaCl2; treatments were compared to unsprayed poinsettias, or plants sprayed with either deionized (DI) water, 4 mm SrCl2, 4 mm NaCl, 4 mm MgCl2, or a solution of Na2SiO3 plus CaCl2 (1 or 2 mm each). At harvest (38 days after initial anthesis), 40.6% of the bracts on unsprayed plants and 35.8% of the bracts on DI water sprayed plants had BN. In contrasts, only 5.3% of the bracts on the 4 mm CaCl2 treated plants and 5.9% of the bracts on 4 mm Na2SiO3 treated plants had BN. Plants sprayed with 4 mm SrCl2 or the combination of 2 mm Na2SiO3 plus 2 mm CaCl2 developed BN on 7.8% and 9.2% of bracts, respectively. NaCl and MgCl2 sprays (4 mm) were not as effective (29.6 and 26.4% BN) as Ca, Si, or Sr sprays at suppressing BN over the duration of this study.

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