ARS | Publication request: Shoot growth and fruit cracking in 'Stayman' apple treated with prohexadione-calcium and GA4/7

Submitted to: Annual Cumberland Shenandoah Fruit Workers Conference
Publication Type: Proceedings
Publication Acceptance Date: March 16, 2007
Publication Date: April 1, 2007
Citation: Miller, S.S. 2007. Shoot growth and fruit cracking in 'Stayman' apple treated with prohexadione-calcium and GA4/7. Annual Cumberland Shenandoah Fruit Workers Conference.

Technical Abstract: The ‘Stayman’ apple (Malus x domestica Borkh.) is a high quality apple with good fresh fruit and processing characteristics. ‘Stayman’ is grown in large numbers in the Mid-Atlantic region where trees are of moderate to high vigor. ‘Stayman’, however is prone to skin cracking which in some seasons can result in losses that exceed 60 to 80 percent of the crop. A series of experiments was 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 fruit 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 percent increase in the incidence of cracking. Including any one of five adjuvants to the PCa + AMS spray increased cracking by 77 percent to 178 percent 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.