Effects of Prohexadione-Ca and GA4+7 on Scarf Skin and Fruit Maturity in Apple

Abstract

Nutrient release characteristics of four different controlled-release fertilizers (Osmocote, Nutricote, Polyon, and Multicote) were monitored during an 11-month period in a simulated outdoor nursery production facility. Although no plants were used in the experiment, fertilization rates, irrigation regimes, and cultural practices simulated those typically used to produce fast-growing, high-nutrient-requiring containerized woody ornamentals. Fertilizer prill release characteristics were monitored through analyses of leachates, which were collected weekly. Concentrations of Mg, Mn, Zn, Cu, and Mo were relatively high during the first 5 to 10 weeks of the experiment, then declined and usually stabilized during the remainder of the study. However, Mn and Zn displayed erratic increases in concentrations several times throughout the study. Calcium concentrations did not increase until the fifth week, rapidly peaked to about 300 mgÁL -1 , and then decreased and leveled off to %80 to 100 mgÁL -1 during the remainder of the study. Several significant differences were observed between treatments. The Osmocote treatment had significantly greater Ca and Mg concentrations in the leachate than the other fertilizer types during the last 6 weeks of the study, whereas the Nutricote treatment often had significantly greater Fe concentrations than leachates from other treatments, especially during the last 26 to 35 weeks of the study, and significantly greater Zn concentrations than the other CRFs during the last 21 weeks of the study. Based upon U.S. Environmental Protection Agency guidelines, concentrations of Fe were often more than the allowable limit of 0.3 mgÁL -1 with all fertilizer types, but especially with Nutricote. Concentrations of Mn and Cu also exceeded federal guidelines, particularly during the first several weeks of the study.

Prohexadione-Ca Reduces Russet and Does Not Negate the Efficacy of GA4+7 Sprays for Russet Control on ‘Golden Delicious’ Apples

“…The effects of combining a single application of P-Ca at PF with three or four GA 4+7 sprays on russet were additive as determined by the lack of an interaction term in a factorial analysis of the data in the present experiments. This result is in agreement with previous studies on a different skin disorder of apple fruit (scarf skin), in which the combination of P-Ca with the first of three GA 4+7 sprays was more effective than either material alone (McArtney et al, 2006). These results are not consistent with the findings of Miller (1998), who reported that P-Ca sprays did not affect the activity of a GA 4+7 program for russet control on 'Golden Delicious' in two different experiments.…”

“…The main effect of P-Ca on mean fruit weight at harvest was neutral; however, P-Ca reduced fruit weight in three of the four experiments in the current study. In a previous study, we also found that P-Ca reduced mean fruit weight (McArtney et al, 2006). Because the effects of P-Ca on fruit set were only measured in one of the four experiments reported here, it is not known at this time if the fruit size response is a direct effect of the combined treatment on fruit growth or if it is mediated by a crop load effect.…”

“…Tromp (1982) found that GA 4+7 did not actively promote shoot growth in apples, even at concentrations as high as 500 mgÁL -1 . Others have reported a slight antagonizing effect on shoot growth when P-Ca was applied with GA 4+7 (McArtney et al, 2006;Miller, 1998;Miller et al, 2002;Schroeder et al, 2003). Treatment effects on shoot length were only recorded 30 d after PF in the present study, and it would be logical to assume that final shoot length should not be greatly affected by a single application of P-Ca at PF.…”

“…However, GA 4+7 sprays for russet control did reduce the level of shoot growth control normally obtained with multiple P-Ca sprays. We recently reported that a single application of P-Ca at PF reduced the severity of another skin defect of apple (scarf skin) and furthermore, the efficacy of multiple GA 4+7 sprays for scarf skin control was in fact increased when P-Ca was applied either in mixture or within 2 d of the first GA 4+7 application (McArtney et al, 2006). However, we also reported that mean fruit weight at harvest was occasionally reduced by the combination of P-Ca and GA 4+7 sprays.…”

Interactive effects of 6-BA, GA4+7 and prohexadione-calcium on ‘Gala’ apples

“…In 2011, P-Ca alone reduced scarf skin by 7% compared with the untreated control (P = 0.0046); however, this effect was negated when combined with GA 4+7 + 6-BA. These data are consistent with other reports in the literature that found a reduction in scarf skin associated with GA 4+7 and P-Ca (McArtney et al 2006).…”