SOME EFFECTS OF SOIL-APPLIED PACLOBUTRAZOL ON PERFORMANCE OF SUNDROP APRICOT (PRUNUS-ARMENIACA L) TREES AND ON RESIDUE IN THE SOIL

Twelve-year-old 'Sundrop' apricot (Prunus armeniaca L.) trees were tre ated with a single soil application of paclobutrazol (PBZ) at the rate of 2, 4, and 6 g of active ingredient per tree. The chemical was appl ied as a trunk drench. Regardless of rate, PBZ treated trees had signi ficantly reduced most vegetative growth characteristics and pruning re quirements as compared with control trees. A rate of 2 g PBZ/tree effe ctively controlled vegetative growth for 3 years. Bioassay with broad bean (Vicia faba L.) confirmed that PBZ was still present in the treat ed soil almost 3 years after application. The extent of growth suppres sion of the indicator plants was in direct relation to the treatment r ate.