2019 ASHS Annual Conference

Ethylene is a gaseous plant hormone serving critical roles in many plant processes, including plant growth, development, plant resiliency to abiotic stress, pathogen infection, seed germination and fruit ripening. The commercial product ethephon is applied to Prunus cerasus ‘Montmorency’ tart cherry orchards to promote uniform fruit abscission and facilitate mechanical harvest operations. Ethephon releases ethylene during degradation. There is also a need to abscise flowers and/or young developing fruitlets on young ‘Montmorency’ trees in order to promote canopy development and, more recently, as a means to reduce increased spotted wing drosophila (SWD) pressure. We initiated a study to determine the potential of ethephon as a fruitlet abscission agent. Rates of 50, 100, 200 and 400 ppm were applied at individual phenology stages (either ‘first white’, 50% full bloom, full bloom, ‘petal fall’ or ‘shuck split’) and compared to a non-treated control and the ethylene inhibitor, aminoethoxyvinilglycine (AVG) as the commercial product, ReTain (133 ppm). The study was replicated at two sites, Traverse City and Clarksville, Michigan. Each treatment was applied to four or five single-tree replicates, depending on the site. Flowers and fruitlets were collected every two to three days for several weeks, beginning the day of application, weighed and placed in sealed tubes to capture headspace gas. A gas chromatograph was used to quantify ethylene. Ethylene production rate of flowers and fruit increased relative to ethephon rate (~25 times at 400 ppm compared to the non-treated control). Ethylene production remained higher for ~five days following applications, irrespective of application timing. Natural ethylene production rate was quite low and AVG practically eliminated ethylene production. The effect of ethephon on fruit abscission differed between sites. At Clarksville, only minor reductions in fruit set were observed and these were not significant, irrespective of application timing or rate. At Traverse City, rates of 200 and 400 ppm reduced fruit set to ~80% and 100% of the non-treated control, but only at the petal fall timing. Temperatures during the petal fall application exceeded 27°C. Based on these data and preliminary data from 2017, temperature plays a far greater role in ethylene induced abscission than the fruit developmental stage. Higher ethephon rates may be required when temperatures are below 27°C. AVG had no effect on fruit set. Despite the relatively low fruit set of Montmorency (~20%), natural ethylene production rate of flowers and fruitlets does not appear to limit fruit set.