Effects of Flurprimidol and Fertilization On Growth Regulation of Knockout® Rose In Landscapes

Knockout^® roses are popular shrub roses that are more disease resistant and have become popular in southern landscapes.  They can easily grow to 5 feet tall and require regular trimming.  Plant growth regulators such as gibberellic acid biosynthesis inhibitors may reduce shoot growth thus reduce labor requirement for maintaining a rose planting.  Two experiments were conducted to evaluate the effects of granular flurprimidol (Cutless 0.33 G) and controlled-release fertilizer (CRF) Osmocote 14-14-14 on Knockout^® Red roses established in landscape beds.  In experiment 1, Cutless .33G was applied at 0, 5, 10, or 20 lb/1000 ft² (0, 0.7, 1.5, or 3 pounds a.i. per acre) as single applications in spring or two applications of 5 and 10 lb/1000 ft² applied at 3 month apart in spring and late-summer.  In Experiment 2, Cutless .33G was applied at 0, 7 or 14 lb/1000 ft² to plants being fertilized with CRF at 0, 2, or 4 lb/1000 ft² nitrogen rates with the 4 lb/1000 ft² treatment applied as two applicaitons.  In experiment 1, Plant size index at September 2010 and March 2011 indicated that two applications at 10 lb/1000 ft² product provided prolonged growth control without the need for trimming.  This treatment also resulted in more flowers and higher overall visual quality among all treatments.  In experiment 2, plants treated with 14 lb/1000 ft2 Cutless and fertilized with 4 lb/1000 ft² N rate had the highest visual quality.  In both experiments, plants treated with flurprimidol had darker foliage than untreated plants.  

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