Soil Texture and Moisture Availability Impacts on the Efficacy of Soil-Applied Paclobutrazol

Abstract

Soil-applied paclobutrazol has been shown to reduce tree growth and pruning costs in trees occupying utility rights-of-way. Uptake and efficacy of soil applied chemicals is often influenced by soil texture and moisture status at the time of application. To test the influence of these conditions on paclobutrazol efficacy, Profile 2SC growth regulator (DowElanco) was applied at three rates (control, 0.3 or 0.6 ml ai/cm stem diameter) to potted sweetgum and white pine seedlings under factorial combinations of soil texture (clay loam or sandy clay loam) and water availability (drought or well-watered). Under well-watered conditions, terminal leader elongation was reduced 53 and 23% by paclobutrazol for sweetgum {Liquidambar styraciflua) and white pine {Pinus strobus), respectively. Sweetgum shoot elongation was responsive to paclobutrazol in the clay loam, but not the sandy clay loam soil. Sweetgum total leaf area and specific leaf area and white pine needle length were reduced by paclobutrazol treatments across water availabilities and soil textures. The results of this study suggest that drought during and following application of paclobutrazol does not reduce efficacy of this chemical. Further research is needed to clarify the impact of soil texture on paclobutrazol efficacy.