A preliminary evaluation of ethephon and naphthaleneacetic acid as deblossoming agents in blueberries

Abstract: Removing flowers to prevent fruit set is a common practise to direct plant resource allocation towards improved shoot and root growth in young blueberry plants. As the current approach of manual deblossoming is labor-intensive, a chemical alternative could benefit blueberry growers. Various growth regulators and caustic chemicals are being used in other crops for preventing fruit set. However, it is unclear if they can be effective in blueberries, particularly due to their urceolate flower shape that prevents direct exposure of flower parts to spray reagents. Here, we conducted a preliminary study to understand the deblossoming efficacy and phytotoxic risks of plant growth regulators ethephon and naphthaleneacetic acid (NAA) in blueberries. The study was conducted in a five-year-old ‘Duke’ planting and included 16 different treatments, composed of different rates of the synthetic auxin, NAA (20-120 PPM), an ethylene releasing agent, ethephon (500-16,000 PPM), or their combinations. Treatments were made as single applications at full bloom or split applications at early and full bloom. The NAA treatments caused at least some phytotoxicity, even at the lowest concentration tested, but showed no strong deblossoming effect. Lower concentrations of ethephon reduced fruit set and higher concentrations were phytotoxic. Mixing with NAA did not increase the deblossoming efficacy of ethephon. Our results suggest that ethephon has the potential for use in deblossoming of blueberry, but a standalone treatment may not be sufficient for the complete elimination of fruit set.