ARS | Publication request: Return bloom in 'Stayman' apple with NAA and/or ethephon: 2007 through 2009

Submitted to: Annual Cumberland Shenandoah Fruit Workers Conference
Publication Type: Proceedings
Publication Acceptance Date: February 5, 2010
Publication Date: March 23, 2010
Citation: Miller, S.S., Crim, V.L. 2010. Return bloom in 'Stayman' apple with NAA and/or ethephon: 2007 through 2009. Annual Cumberland Shenandoah Fruit Workers Conference.

Technical Abstract: Following a season in which apple trees produce a full crop, many cultivars fail to produce enough bloom the next year for an adequate crop. Obtaining good return bloom is a problem for many apple growers. Plant growth regulators (PGRs) are recommended to enhance return bloom in apple. This study examines the effect of multiple sprays of two PGRs, 1-naphthalenacetic acid (NAA) and/or (2-chloroethyl) phosphonic acid (ethephon), applied during the growing season on return bloom in the 'Stayman' apple cultivar. Treatments were applied dilute with a handgun sprayer beginning in 2007 and repeated in 2008 and 2009. In addition to a hand-thinned and a non-thinned control, treatments included: a chemically thinned (CT) only spray (NAA in 2007 and carbaryl + oil in 2008 and 2009); four bi-weekly NAA sprays at 5 ppm beginning 6 weeks after full bloom (WAFB) ("Summer NAA"); four weekly NAA sprays at 5 ppm beginning 4 weeks before harvest ("Pre-harvest NAA"); four bi-weekly ethephon sprays at 150 ppm beginning 6 WAFB (Ethephon); and a combined treatment of summer NAA and ethephon. All NAA and ethephon treated trees received the CT spray at the commercial recommended fruit size stage. Ethephon and summer NAA + ethephon applied in 2007 increased return bloom compared to the control and CT only treatments in 2008. Ethephon alone applied in 2008 increased return bloom in 2009 compared to the non-thinned control (p = 0.0219) and the hand thinned control (p = 0.0210) (SAS PROC MIXED at 5 percent). Summer or pre-harvest NAA treatments increased return bloom slightly in 2008 and 2009, but the difference was not significant from the control treatments. None of the treatments affected pre-harvest fruit drop. Pre-harvest NAA advanced fruit maturity (based on starch index rating) in all three years and ethephon advanced maturity in 2008 and 2009 compared to the non-thinned and hand thinned controls. Additional data are needed to determine if ethephon provides an economic benefit from the enhanced return bloom.