John A. Cline

Effect of gibberellic acid on fruit cracking and quality of Bing and Sam sweet cherries

Rain-induced cracking of sweet cherries (Prunus avium L.) is a major problem in many cherry growing regions throughout the world. One method to reduce cracking is to grow cracking resistant cultivars; however, no completely effective control measures are currently available to eliminate this problem. Studies conducted in New Zealand to test the ameliorating properties of gibberellic acid sprays to reduce cracking were examined. The results revealed that repeated or singular foliar applications at 10 or 40 mg L-1 gibberellic acid (GA3), respectively, increased both fruit cracking, and fruit firmness, but delayed fruit colour development. Key words: Prunus avium, cherry splitting, cracking

Mechanical blossom thinning of apples and influence on yield, fruit quality and spur leaf area

McClure, K. A. and Cline, J. A. 2015. Mechanical blossom thinning of apples and influence on yield, fruit quality and spur leaf area. Can. J. Plant Sci. 95: 887-896. Apple (Malus×domestica Borkh.) trees tend to crop heavily, which often makes crop load adjustment necessary. This can now be achieved as early as bloom by mechanical removal/thinning of blossoms. High-density Empire/M.26 and Royal Gala/M.26 apple trees were mechanically (MBT) and hand blossom thinned (HBT) in 2010 and 2011, respectively, and their effects on fruit set, subsequent hand thinning, final crop load, and spur leaf area were measured. In both years, MBT effectively thinned trees and reduced fruit set, but did not reduce the requirement for follow-up hand fruitlet thinning after June drop in 2011. In 2010, harvest yields for MBT treatments decreased, while weight and diameter increased. In 2011, most harvest and fruit quality parameters were unaffected by thinning. Trees that were mechanically thinned had significantly reduced spur leaf area, but were similar to unthinned control trees with respect to many of the yield and quality parameters measured. Mechanical blossom thinning is a new crop load management option for apple growers looking to supplement more traditional chemical and hand thinning techniques.

Diurnal spray timing does not affect the thinning of apples with carbaryl, benzyladenine, and napthaleneacetic acid

Inclement weather during fruit set of apples [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] can restrict an orchardists ability to apply chemical thinners in a timely fashion. While recommendations for the timing of chemical thinners are very specific to the phenological stage of development and the environmental conditions following spray application, few studies have addressed the influence of diurnal timing and environmental conditions at the time of application on treatment efficacy. This 2-yr study was designed to determine the effect of diurnal spray timing and product on the thinning of mature Empire/M.26 apple trees. Treatments of 10 mg L-1 1-napthaleneacetic acid (NAA), 75 mg L-1 N-(phenylmethyl)-1H-purine-6-amine (6-benzyladenine) (BA), and 750 mg L-1 1-napthyl-N-methylcarbamate (CB) were applied at approximately 6-h intervals over a 24-h period when the largest fruitlets were 10–12 mm in diameter. Environmental conditions at the time of spraying in both years ranged from very cool...

AVG, NAA, boron, and magnesium influence preharvest fruit drop and fruit quality of ‘Honeycrisp’ apples

Abstract: Preharvest fruit drop (PFD) of apple (Malus domestica Borkh.) can cause significant losses resulting in up to 50% reduction in yield in some years. In a 2-yr study, ‘Honeycrisp’ trees were treated with six foliar treatments including 20 mg·L-1 1-naphthaleneacetic acid (NAA) 2 wk before anticipated harvest (WBAH), 125 mg·L-1 aminoethoxyvinylglycine hydrochloride (AVG) 4 WBAH, AVG plus NAA 2 WBAH, and repeat sprays of 200 mg·L-1 B, and 2000 mg·L-1 Mg applied 48–93 d after full bloom to evaluate their effect on PFD and fruit quality. Fruit drop associated with broken pedicels and physiological causes was monitored. During a year with ∼43% PFD on untreated control trees, AVG retained up to ∼35% and NAA retained up to ∼27% of the total fruit number, relative to the control trees. The combination of AVG plus NAA had similar PFD compared with AVG alone, while B and Mg were similar to the control. The proportion of PFD associated with broken pedicels was ∼5%. Aminoethoxyvinylglycine delayed starch degradation, ethylene evolution, and blush skin colour development of fruit. This study supports the use of AVG 4 WBAH and NAA 2 WBAH to manage ‘Honeycrisp’ PFD, which may offer economic advantages for growing quality apples. Foliar sprays of Mg or B failed to reduce PFD.

Prohexadione-calcium, ethephon, trinexapac-ethyl, and maleic hydrazide reduce extension shoot growth of apple

Abstract: Prohexadione-calcium (P-Ca) is widely used to reduce vegetative growth and labour costs associated with manual pruning. Orchard studies were conducted in 2012 and 2013 to determine the response of mature ‘Empire’/M.26 apple trees to individual or combined applications of P-Ca, ethephon (ETH), trinexapac-ethyl (TE), and maleic hydrazide (MH). Sprays were repeated three times at approximately 2-wk intervals starting at petal fall. All compounds reduced extension shoot growth, ranging from 40%–73% in 2012 and 26%–57% in 2013, relative to untreated controls. The greatest reduction in growth was achieved with ETH in one year and P-Ca + ETH and MH in another. The tank-mixed combination of P-Ca + ETH improved vegetative control compared with each compound applied alone. MH caused foliar phytotoxicity and damage to the apical meristem, resulting in the stimulation of lateral shoot growth. Reduction in shoot growth from any of the plant bioregulators (PBR) did not reduce dormant pruning times in the spring following application. Total and marketable fruit yield was unaffected by the PBRs, although applications of MH resulted in a significantly higher number of fruit per tree and crop load but a lower mean fruit weight and percent marketable fruit.