Developing Field Strategies to Correct Alternate Bearing in Avocado Groves

When ‘Hass’ avocado trees produce an on-bloom and set an on-crop, the apical (and axillary) buds on the spring shoots, which would normally produce vegetative shoots during the summer and fall, are inhibited by the young developing fruit. Inhibition of summer shoot growth reduces the number of nodes that can bear floral shoots the next spring. It is important to note that summer shoots contribute > 60% of the spring bloom. The objectives of the research were to adapt prior trunk-injected and foliar-applied PGR treatments that showed promise in overcoming correlative inhibition (auxin > cytokinin) of summer vegetative shoot growth and inhibition of spring bud break (endodormancy, ABA > cytokinin) during the on-crop year as foliar- and irrigation-applied PGR treatments for use on ‘Hass’ avocado. The research was conducted at the South Coast Research and Education Center (SCREC). A commercial (synthetic) cytokinin (6-benzyladenine, 6-BA) plus auxin-transport inhibitor (triiodobenzoic acid, TIBA) treatment was compared with a proprietary (naturally plant product) cytokinin (PCK) plus auxin-transport inhibitor (NATI) treatment. The PGR combinations were applied in July 2012 and again in January 2013 as foliar-sprays (100 mg/L each). In this experiment, a second set of on-crop trees was treated again during the putative of-crop year. This experiment also included inflorescence pruning, in which 3 out of 10 major floral branches were removed (J. Dixon) and S-abscisic acid (S-ABA, a growth inhibitor) sprayed in spring 2012 at 500 and 2000 mg/L in an 18”-wide strip on two sides of the tree parallel to the row. Both treatments were designed to reduce fruit set by the on-bloom sufficiently early to increase the yield of large size fruit in the on-crop year and total yield the following year. In a second experiment, 6-BA and TIBA were applied through the irrigation system (4 g each/tree). To test the concept, 6-BA plus TIBA were sprayed directly onto the soil under the canopy of each tree (4 g each/tree) and mulch under each tree was removed before the soil spray