Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2007
Publication Date: 10/1/2007
Citation: Miller, S.S. 2007. Prohexadione-calcium (Apogee) Reduces Both Shoot Growth and the Efficacy of GA4+7 (ProVide) Used to Suppress 'Stayman' Apple Cracking. HortTechnology. Vol. 17, p 1-9. Interpretive Summary: Shoot growth control is an important aspect of apple culture. A plant growth regulator (PGR), prohexadione-calcium (PCa) (Apogee), has proven to be an excellent non-residual bioregulator for suppressing excess shoot growth in apple trees. The Stayman apple cultivar is a high quality culinary and processing apple that is subject to a physiological disorder known as Stayman cracking. Fruit losses from this disorder may reach 80% in some years. Another PGR, gibberellin A4 + A7 (GA4/7) has been shown to reduce the severity of Stayman cracking. Field studies were conducted over five years to examine the interaction of PCa, an anti-gibberellin, and GA4/7 on growth and the incidence of cracking in Stayman apple. PCa reduced shoot growth but increased cracking. GA4/7 reduced the incidence of cracking, but generally was unable to completely negate the effect of PCa to increase fruit cracking. This information is valuable to researchers studying fruit cracking, fruit extension specialist who provides production recommendations, and apple growers producing Stayman apple.
Technical Abstract: The ‘Stayman Winesap’ apple (Malus xdomestica Borkh.) is a high quality apple with good fresh fruit and processing characteristics. Trees are of moderate to high vigor where it is grown in large numbers in the Mid-Atlantic region. ‘Stayman’, however is prone to skin cracking which in some seasons can result in losses that exceed 60 to 80% of the crop. A series of experiments were conducted between 1997 and 2001 to examine the effect of prohexadione-calcium (PCa) and the proprietary mixture of gibberellins A4 plus A7 (GA4+7) (ProVide) on shoot growth and cracking in the ‘Stayman 201’ apple cultivar. PCa consistently reduced terminal shoot growth when applied in one, two, or three sprays between petal fall (PF) and PF + 6 weeks (postbloom), but this timing of application had no effect on the growth of water sprouts. PCa sprays applied during July and Aug. (preharvest) reduced the growth of water sprouts. The level of cracking varied with year, but in general GA4+7 applied in five bi-weekly preharvest sprays reduced the incidence of cracking. PCa increased the incidence of cracking in most, but not all, experiments. In those trials where postbloom PCa did not result in a significant increase in cracking there was a definite trend toward more cracking. GA4+7 applied preharvest partially or completely reversed the effect of postbloom PCa on fruit cracking compared to the untreated controls. In one experiment, PCa + ammonium sulfate (AMS) as a water conditioner applied without an adjuvant showed a 43% increase in the incidence of cracking. Including any one of five adjuvants to the PCa + AMS spray increased cracking by 77% to 178% above the level of cracking in the untreated controls. The use of PCa to suppress shoot growth in bearing ‘Stayman’ apple trees is not recommended because of the potential for increased fruit cracking.