Adjusting the crop load of peaches [Prunus persica (L.) Batsch] by hand thinning is currently required to ensure marketable size of most cultivars grown in Ontario. A novel approach to adjust cropping by inhibiting flowering using gibberellic acid (GA3) was tested in an orchard experiment in which GA3 was applied at 7, 10, and 13 weeks after full bloom to mature `Redhaven' peach trees. Late GA3 treatments increased soluble solids concentration (SSC) in the season of application. A significant interaction between GA3 rate and time of application was observed on increased fruit firmness in the current season. Increasing rates of GA3 decreased flowering the following season in a quadratic fashion, resulting in a 41% to 90% diminished requirement for hand thinning. This translated into lower crop loads and yields for GA3-treated trees at harvest compared with untreated control trees. However, GA3-treated trees had larger mean fruit size and improved fruit size distribution the year after GA3 application. Advanced fruit ripening was also evident by increased fruit SSC and decreased fruit firmness, likely an indirect effect of GA3 on crop load. GA3 application timing significantly increased overall tree growth measured by the changes in trunk cross-sectional area.
Elina Coneva and John A. Cline
John A. Cline and Eric J. Hanson
Individual fruit of `Delicious' apple (Malus domestica Borkh.) were exposed to low, high, or ambient relative humidity (RH) levels during different stages of fruit development to study the importance of transpiration and the xylem system in supplying Ca to fruit. The Ca content of fruit exposed to low RH was the same or higher than that of fruit exposed to high RH. Treatments imposed early or late in the season usually affected fruit Ca levels similarly. Fruit weight was not consistently affected by RH treatments. The xylem may be a significant source of fruit Ca throughout the season.
Elina D. Coneva and John A. Cline
The purpose of this research was to determine the effectiveness of three blossom-thinning compounds on crop density and fruit quality of two peach cultivars. Treatments consisted of 15 ml·L–1 and 30 ml·L–1 ammonium thiosulphate, 30 ml·L–1 and 40 ml·L–1 decyl alcohol, and 40 ml·L–1 lime sulfur. Treatments were applied to `Redhaven' and `Harrow Diamond' peach trees at two phenological stages: 80%, and 100% full bloom in 2002 and 2003. In both years, treatments reduced the crop density in both cultivars, and in 2003 the amount of hand thinning required to adjust the crop load was significantly reduced. Fruit size from several blossom-thinned treatments was comparable with that observed from hand-thinned trees. However, treatments caused significant leaf phytotoxicity to `Harrow Diamond' trees in 2003, likely a result of hand spray gun applications. These data indicate that chemical sprays at bloom can be used successfully to reduce fruit set, but are very environmentally, dose, and cultivar dependent.
John A. Cline and Tony D. Webster
For many years, researchers and growers have attempted to find methods to alleviate the rain-induced cracking of sweet cherries. Cracking is thought to be caused primarily by the osmotic uptake of rain water through the fruit skin. A 3-year study was conducted at East Malling to test the hypotheses that rain covers reduce, while irrigation increases, fruit cracking. Two types of rain shelters, with and without trickle irrigation, were compared against control treatments on 8-year-old `Merchant'/Colt trees. Covers reduced cracked fruit by up to 11% in 1991, 7% in 1992, and 25% in 1993 when natural cracking on uncovered trees was ≈20%, 25%, and 40%, respectively. Trickle irrigation was associated with a 6% increase in fruit cracking in all 3 years. Tree covers and irrigation also tended to increase fruit size and maturity. Fruits from beneath covers were lower in soluble solids concentration and were firmer in comparison with fruits from uncovered trees. This study indicates that tree covers, while affording some protection against rain-induced cracking, do not altogether prevent the problem. Furthermore, irrigation appears to aggravate cracking when used with tree covers. A mechanism for cracking under covers will be discussed in relation to rainfall, fruit transpiration, and tree water relations.
Derek J. Plotkowski and John A. Cline
Insufficient biologically available nitrogen (N) for yeast is a persistent issue facing cidermakers, whose apple juice base usually does not provide adequate nutrition for a complete fermentation. Cidermakers often supplement their juice with additional yeast assimilable nitrogen (YAN) in the cellar to aid fermentation. The development of biologically available N in apple juice is not well understood. In this study, juice samples from ‘Crimson Crisp®’ apples were taken at several sampling dates in the 2016, 2017, and 2018 growing seasons and analyzed for YAN using formol titration and high-performance liquid chromatography. It was observed that while the total YAN concentration in these apples drops from the period shortly after fruit set to the end of summer, YAN remains stable from several weeks before harvest until the date of harvest. The total YAN did not change after a 6-week postharvest storage period. By contrast, the individual amino acid components of YAN do change during this period. This experiment shows that foliar urea sprays in ‘Crimson Crisp®’ produce an increase in organic N in the juice, mostly in the form of asparagine. Increased organic N impacts yeast growth and sensory characteristics of cider and may be seen as desirable by cider producers.
Eugene J. Hogue, John A. Cline, Gerry Neilsen, and Denise Neilsen
Fertigated ‘Gala’ apple trees on M.9 (Malus domestica Borkh.) rootstock, planted in 1998, were grown on a coarse soil for 6 years (1998 to 2003) and exposed to eight orchard floor vegetation management treatments within the tree row. These consisted of a glyphosate control; three waste paper mulch treatments [spray-on mulch paper mulch (SM), SM incorporated with dichlobenil, SM applied over uniformly spread shredded office paper (SOP)]; and four living cover crop mulch treatments [dwarf white clover (WC), sweet clover (SC), hairy vetch (HV), and annual rye]. There were no significant treatment effects on leaf nitrogen (N) and phosphorus (P) status; however, leaf potassium (K) levels were negatively affected by the living mulch treatments in 2 of 5 years. Tree vigor was diminished by several of the orchard floor vegetation management systems in 5 of 6 years. Trees receiving an SM treatment grew more rapidly than trees receiving the ground cover treatments and trees receiving a glyphosate treatment had relatively poor but comparable growth to several of the cover crop treatments. Growth response in trees receiving SM were observed in all production years. After 6 years, cumulative yields were highest from trees receiving any of the three SM or glyphosate treatments and significantly less for any of the ground cover treatments. Weed growth within the rye cover crop was significantly reduced in comparison with the other living mulches; however, it remained sufficiently competitive to contribute to diminished overall yield and tree growth in comparison with the SM and gylphosate control treatments. Overall, response of leaf K concentration to mulch treatments was insufficient to prevent low K levels after 5 years. The addition of K through the organic mulches or recycling of K by cover crops was insufficient to avoid the development of low leaf K levels. Annual fertigation of K, in addition to N and P, appears necessary to maintain adequate vigor and yield when using mulches or cover crops in intensive, drip-irrigated apple orchards grown on coarse soils.
John A. Cline, Mary Bom, and Donald C. Elfving
A series of seven fruit thinning experiments with benzyladenine (BA), benzyladenine and GA4+7 (10:1 BA:GA4+7, Accel), carbaryl (CB), and NAA were conducted at the Horticultural Experiment Station, Simcoe, during the 1993 and 1994 growing seasons. In 1993, BA and Accel at 0, 100, 200, and 300 mg of BA/liter were applied to mature `Redspur Delicious'/M.26 and `Empire'/M.26 trees when fruit were ≈10 mm in diameter. In one set of experiments in 1994, Accel was applied at 0, 25, 50, 100, 150, and 200 mg of BA/liter to mature `McIntosh'/M.26 and `Empire'/M.7 trees. In a second set of experiments in 1994, Accel was applied at 0, 50, and 100 mg of BA/liter to mature `Idared'/M.26, `Empire'/M.26, and `Marshall McIntosh'/Mark trees when fruit were ≈10 mm in diameter. Additional treatments included bloom sprays of Accel at 50 mg of BA/liter, and sprays of BA at 50 mg a.i/liter, NAA at 10 mg a.i./liter, CB at 1000 mg a.i./liter, and a “low” (two fruit remaining/flower cluster) and `”high” (one fruit remaining/flower cluster) rate of hand thinning. In all experiments, thinning response to BA and Accel increased with concentration. Concentrations below 50, 100, and 300 mg BA/liter were generally ineffective for thinning `Empire', `Idared', and `McIntosh', and `Delicious', respectively. Fruit size of `Idared' and `Empire' was increased at rates of 50 mg BA/liter, whereas rates of 100 mg BA/liter were needed to increase fruit size of `McIntosh'. Accel applied to `Empire' at 150 mg BA/liter decreased the number of seeds per fruit and increased fruit length:diameter (L:D) ratios. Concentrations of Accel exceeding 100 mg BA/liter in `Red Delicious' decreased the number of seeds per fruit, while having little effect on fruit L:D ratios even though lower concentrations increased fruit L:D ratios. Diametric fruit growth measurements in 1994 indicated a temporary, but sharp, decline in growth rate immediately following treatment imposition for trees that responded positively to thinning. Additional data describing treatment effects on fruit size distribution, vegetative growth, and fruit maturity will be presented and discussed in relation to crop load.
Richard P. Marini, John A. Barden, John A. Cline, Ronald L. Perry, and Terence Robinson
The influence of rootstock on average fruit weight was evaluated for a subset of data from a multilocation NC-140 apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] rootstock trial. Data for eight dwarf rootstocks were collected at four locations for 2 years. Analysis of covariance was used to evaluate the effect of rootstock on average fruit weight when crop density or number of fruit per tree was included in the linear model as a covariate. When number of fruit harvested per tree was used as a covariate, average fruit weight was not affected by rootstock in either year in Ontario. In Michigan and Virginia, rootstock and number of fruit per tree, but not the rootstock × number of fruit interaction, were significant, so common slopes models were used to estimate least squares means for average fruit weight. In general, trees on M.27 and P.1 produced the smallest fruit, and trees on B.9, M.9 EMLA, and Mac.39 produced the largest fruit. In New York the interaction of rootstock × number of fruit was significant, so least squares means were estimated at three levels of number of fruit per tree. Both years, at all levels of number of fruit, trees on M.26 EMLA produced the smallest fruit and trees on M.27 EMLA produced the largest fruit. Average fruit weight was most affected by number of fruit per tree when Mark was the rootstock. In general, results were similar when crop density was used as the covariate, except that trees on M.27 EMLA did not produce small fruit in Michigan and Ontario.
Renae E. Moran, Bryan J. Peterson, Gennaro Fazio, and John A. Cline
The goal of this research was to evaluate resistance of apple rootstocks to late winter deacclimation during a 2-day exposure to warm temperatures in Maine. We measured the cold temperature tolerance of xylem, phloem, and cambium from 0 to −40 °C in 1- and 2-year-old shoot pieces from apple rootstock cultivars and advanced selections ‘M.9 T337’ (M.9), ‘M.7 EMLA’ (M.7), ‘Budagovsky 9’ (B.9), ‘Geneva® 41’ (G.41), ‘Geneva 30’ (G.30), ‘Geneva 935’ (G.935), ‘Geneva 814’ (G.814), G.4013, G.5257, and Vineland 6 (V.6) after a 2-day exposure to warm (22 °C) or cold (2 to 4 °C) temperatures. Injury was measured on a 0 to 10 rating scale based on percentage of discolored cross-sectional xylem and phloem, and cambial length and circumference with brown discoloration, with 0 indicating no browning and 10 indicating browning in the entire tissue. Injury was also measured as intensity of browning on a scale of 0 (no browning) to 5 (dark brown to black). The weighted averages of the two ratings were used to calculate an index of browning. Genotypic variation occurred in the degree of deacclimation, which ranged from none to as much as 15 °C loss in hardiness. Two genotypes, ‘G.41’ and ‘M.9’, showed little change in hardiness in both years they were tested. Two genotypes, G.4013 and ‘G.814’, lost substantial hardiness in both years and may be vulnerable to late winter freeze-thaw events, but were among the hardiest before deacclimation. ‘G.935’ and G.5257 showed a small loss of hardiness, whereas ‘B.9’ lost hardiness in the cambium, but not the xylem, and V.6 lost hardiness after warm exposure, but showed almost no injury at temperatures as cold as −35 °C. The loss of hardiness of these four genotypes that were tested in only one year should be verified with additional testing because of the potential for yearly variation.