2017 ASHS Annual Conference

Successful commercial pecan [Carya illinoinensis (Wangenh.) K. Koch] production relies heavily on mitigation of alternate bearing, a propensity to have alternating heavy (‘on’) and light (‘off’) year crop loads. Alternate bearing is a function of pistillate flower production at the shoot level. Mechanisms of floral initiation in pecan are not well understood. Our objective was to assess the impact of select plant growth regulators (PGRs) on return bloom for potential commercial application in pecan. A two-year study evaluated effects of ethephon (Ethepon2^® [100 mg∙L^–1 a.i.]), aminoethoxyvinylglycine (AVG; as ReTain^® [88 mg∙L^–1 a.i.]), and two rates of gibberellic acid (GA_3; ProGibb^® [50 & 100 mg∙L^–1 a.i.]) on subsequent season return bloom in fruiting versus nonfruiting pecan shoots when applied post full bloom. Cultivars used were mature ‘Western’ and immature ‘Western’ and ‘Pawnee’. Effects of PGRs on return bloom of nonfruiting shoots were different than for fruiting shoots. Three late spring applications of the 100 mg∙L^–1 a.i. GA₃ treatment on fruiting shoots of mature ‘Western’ trees increased number of flowers per new shoot by 55.6% compared with the control fruiting shoots. Whereas, for nonfruiting shoots in immature ‘Western’ trees the 100 mg∙L^–1 a.i.GA₃ treatment reduced number of flowers per new shoot in the next season by 88.2%. The total number of new shoots from the previous season nonfruiting shoots in the mature ‘Western’ trees was decreased significantly by all treatments compared to the control nonfruiting shoots, as much as 93.4% for the AVG treatment. Results from immature ‘Pawnee’ shoots did not show statistically significant differences, but followed a similar trend as mature ‘Western’ shoots. The effects of these PGRs on subsequent season flowering in pecan are complex. Successful management of alternate bearing in pecan, as well as in other crops, is highly dependent on the rates and timing of PGR applications. This study offers insights for mitigation of alternate bearing by either increasing subsequent season return bloom with GA₃ application on current season fruiting shoots or reducing the need for fruit thinning in an ‘on’ year by applying PGRs to nonfruiting shoots an entire season in advance.