CHEMICAL AND MECHANICAL THINNING OF PEACHES

Horticultural and economic evaluations of chemical blossom thinners were conducted in 16 commercial orchard trials during 2005 to 2007. The treatments were applied at 80 percent full bloom and compared to hand thinning post-bloom. Chemical efficacy was variable among years and blocks. Chemical thinners decreased follow-up hand thinning time in 33 percent of the trials and increased fruit diameter in 55 percent of the trials, resulting in net impacts of $14 to $983 per acre in 78 percent of the trials. Similar evaluations of mechanical peach thinners were conducted in four commercial orchard blocks in 2007. A mechanical blossom thinner designed by a German grower for thinning apple trees in organic orchards was tested on peach trees trained to either a perpendicular V or quad V system. Thinning was conducted at 20 or 80 percent full bloom. A USDA spiked-drum shaker, originally designed for harvesting citrus, was tested at 45 days after full bloom in two of the same blocks that were mechanically blossom thinned. Mechanical thinners reduced fruit set, decreased follow-up hand thinning time, and increased the number of fruit in the 3-inch or greater size distribution in 100 percent of the trials. Net profits ranged from $71 to $796 per acre. Bloom thinning at 20 percent full bloom was similar to thinning at 80 percent full bloom. Detailed counts of flowers on branches with different orientations indicated that pruning can be adjusted to improve thinner performance.