Effect of plant growth regulators applied during budbreak on pecan nut yield

Four plant growth regulators were applied the last week of March and the first week of April during four consecutive years in order to evaluate their effect on nut yield and quality. Plant growth regulators and rates evaluated were: Biozyme TF (R) (BZ), 1 L cm ha(-1) in each application; Biofrut (R) (BF), 300 g cm ha(-1) in each application; thidiazuron (TDZ), 10 and 5 g a. i. ha(-1) in the first and second application, respectively; and paclobutrazol (PBZ) 200 g a. i. ha(-1). All treatments were sprayed with 1800 L ha(-1) of water but PBZ. PBZ was soil applied only the last three years and it was mixed with water in a ratio of 0.5 g L-1 and then placed in the bottom of eight 20-cm deep holes. The experimental design was a randomized complete block with three replications. Four trees were applied and two central trees were used as the experimental unit. Marketable nut yield was affected significantly during the first year of evaluation. Control treatment yielded 1149 kg ha(-1), while the rest of treatments yielded from 1798 to 2096 kg ha(-1). In the second year, total nut yield varied from 1820 to 2053 kg ha(-1) in all treatments but differences among them were not significant. Also, in the third and fourth year there were no significant differences in nut yield among treatments. TDZ treatment decreased alternate bearing intensity (I) from 0.27 showed in the control treatment, to 0.05. TDZ decreased cumulative I in the third and fourth year of study. Effect on pecan nut weight was not significant and values were inconsistent among treatments and years. The application of plant growth regulators during early shoot growth in pecan trees affected pecan nut yield and I. These results suggest that application of plant growth regulators could help to manipulate yield and alternate bearing in warm regions where chilling is not enough to induce and break a regular dormancy for pecans.