Growth and Landscape Establishment of Pyracantha and Juniperus after Application of Paclobutrazol

Abstract

The long-term effects of paclobutrazol applied to container-grown `Mojave' pyracantha ( Pyracantha ×) and `San Jose' juniper ( Juniperus chinensis L.) were investigated. Paclobutrazol was applied as a drench to container-grown (2.8 liter) plants at the rates of 0, 5, 10, 20, and 40 mg a.i./pot in June 1991, and plants were transplanted to the field in Feb. 1992. Pyracantha plant height, shoot and root dry weight, and total biomass (shoot dry weight + root dry weight) decreased quadratically as rate of paclobutrazol increased during nursery production. Paclobutrazol had no effect on plant height or shoot dry weight of Juniperus , although width indices were reduced. Ratings for root quality for Juniperus in containers increased as rate of paclobutrazol increased. After 9 months in the landscape, paclobutrazol still influenced plant height, width, and shoot dry weight for Pyracantha but had no effect on Juniperus . As rate of application increased, fruit retention on Pyracantha increased. Paclobutrazol applied as a container medium drench at 5 mg a.i./pot was excessive during nursery production of Pyracantha and Juniperus . Chemical name used: [(2 RS , 3 RS )-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-yl)penten-3-ol] (paclobutrazol).