Growth Regulators Applied to Poinsettias in Production Affect Cyathia Drop and Bract Edge Burn in Postproduction

In the production of poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch), the use of a combination of 6-Benzylaminopurine and Gibberellins A₄&A₇ (BA/GA) for expanding bract size and the use of paclobutrazol are expanding.  Preliminary studies indicated that these chemicals may be affecting the occurrence of cyathia drop and Bract Edge Burn (BEB), which is often associated with Botrytis.  Two experiments were conducted in 2012 to further evaluate this relationship.  For both, plants were grown using standard production procedures.  The BA/GA (Fascination) was applied at a concentration of 5 mg·L^-1 for each chemical using a spray volume of 200 mL·m^-2.   At the end of the production phase, the plants were sleeved and moved (shipping) to a dark room for 3 days.  Then plants were unsleeved and placed in a postproduction room with 12 hours of lights.  In postproduction, the numbers of cyathia that were developing and still attached to the plant were counted on 2 laterals on each plant.  With ‘Early Prestige Red’ 7 days after shipping (DAS), the numbers of cyathia per shoot on control plants, on plants only drenched with paclobutrazol (1 mg·L^-1) and on plants sprayed with only BA/GA were 3.6, 6.1 and 0.8, respectively.  Paclobutrazol and BA/GA applications were 7 days before shipping (DBS).  For plants sprayed with BA/GA and drenched with paclobutrazol, the number of cyathia were 1.3, 2.6, 2.0, and 3.2 when the drench was applied 1, 7, 14, or 21 DBS, respectively.  For plants sprayed with BA/GA and with paclobutrazol (20 mg·L^-1) 7 DBS, the number of cyathia was 6.1.  With ‘Prestige Red’ 10 DAS, plants sprayed with paclobutrazol (30 mg·L^-1) had more cyathia than did plants drenched with paclobutrazol (1 mg·L^-1).  Paclobutrazol reduced cyathia drop better when applied 5 or 14 DBS compared to 2 DBS.  Plants given BA/GA and sprayed with paclobutrazol had twice as many cyathia compared to plants only sprayed with BA/GA.  Occurrence of BEB was determined using a whole-plant rating scale with 1 = best and 5 = worse.  BEB ratings for control plants and ones sprayed or drenched with only paclobutrazol were similar.  Rating for control plants and plants sprayed with BA/GA 14 DBS was 1.8 and 3.4, respectively.  Paclobutrazol sprays 5 or 14 DBS did not reduce the occurrence of BEB in plants sprayed with BA/GA.