`Macoun' is a high-value apple cultivar in the northeastern United States that is very difficult to produce. It is difficult to thin and prone to alternate bearing. `Macoun' is also prone to preharvest drop. Small fruit size, bruising, and lack of red color are additional obstacles to profitable production. The objective of this study was to compare the efficacy of two chemical thinning treatments—accel plus carbaryl, or NAA plus carbaryl—with an untreated control. A second objective was to evaluate the efficacy of ReTain for delaying `Macoun' fruit maturity and to determine if there was an interaction between ReTain and thinning treatment on fruit characteristics at harvest. Both thinning treatments were effective in reducing fruit set in 1997. Accel plus carbaryl was effective again in 1998, while NAA plus carbaryl over-thinned. Accel increased fruit size in 1997 compared to unthinned controls, and both thinning treatments increased fruit size in 1998. Accel increased fruit firmness in both years. ReTain reduced preharvest drop and delayed fruit maturity both years. In 1997, firmness was greatest for fruit treated with accel and ReTain, while ReTain had no effect on firmness of fruit from NAA thinned trees. ReTain had no effect on fruit firmness in 1998.
Effects of chemical thinners on yield, fruit size, and fruit quality was studied in a commercial orchard in Milton, N.Y., on 6-year-old `Honeycrisp'/M.26 trees. The trees were planted at 1.8 × 3.6-m spacing with trickle irrigation and were trained to the vertical axis system. The treatments applied in a randomized complete-block design with four replications were an untreated control; carbaryl (Sevin XLR at 125 mL/100 L); NAA at 2.5 ppm, 5 ppm, or 7.5 ppm; NAA at 2.5 or 5 ppm plus carbaryl; and Accel (a.i. at 74 g·ha-1) plus carbaryl. Chemical thinners were applied to drip with an air-blast sprayer, when the largest fruit were 11.5 mm in diameter. Generally, thinning activity increased with increasing NAA concentration. The combination sprays of 5 ppm NAA plus carbaryl, and Accel plus carbaryl over-thinned `Honeycrisp'. Carbaryl alone was inconsistent. All thinning treatments increased fruit size relative to unthinned trees, with average fruit diameter exceeding 76 mm. `Honeycrisp' is a large-fruited cultivar that is easy to thin chemically at the traditional 10- to 12-mm growth stage. NAA at 2.5 or 5 ppm provided adequate thinning to produce fruit of good quality and size. If initial set is heavy and a stronger thinning response is desired, the combination of 2.5 ppm NAA plus carbaryl could be used. `Honeycrisp' appears to be very sensitive to Accel, when used in combination with Sevin XLR. Further research needed before Accel is used to thin `Honeycrisp'.
J.R. Schupp, H.A. Schupp, and M.H. Bates
A study was conducted in 1992 at Highmoor Farm, Monmouth, ME to test the effects of fish hydrolysate fertilizer on fruit set, fruit size and fruit quality of apple. Mature, semi-dwarf `Delicious' and `Golden Delicious' trees received 2.76g/1 N, supplied by either fish hydrolysate fertilizer or urea, or received no fertilizer (control). Fertilizers were applied via three foliar sprays applied at seven day intervals, beginning at petal fall. Fish hydralysate fertilizer reduced fruit set of `Delicious' and `Golden Delicious'. Foliar urea increased fruit set and yield of 'Golden Delicious'. Neither fertilizer affected mineral nutrient concentrations of leaves collected in July. Fish hydrolysate increased fruit russeting on both cultivars. Fish hydrolysate is not recommended as a foliar fertilizer for apples.
J.R. Schupp and S.I. Koller
The growth, productivity, and fruit characteristics of four summer-ripening disease-resistant apple cultivars, (DRCs), `NY 66305-139', `Williams' Pride', `Redfree', and `Dayton' on M.26 EMLA, M.27 EMLA, or Mark rootstocks were compared. `NY 66305-139' was the earliest-ripening cultivar, with the smallest tree size, lowest yield, and the smallest, softest fruit. `Williams' Pride' trees were large, productive, and produced large fruit with the highest red skin color in this trial. The loss of marketable yield of this cultivar, due to moldy core and bitter pit in 1996, raise concerns about its commercial potential. `Redfree' trees were intermediate among the four cultivars in vigor and precocity, and produced high yields of medium-sized fruit. `Dayton' trees were large, high-yielding, and produced the largest, firmest, sweetest fruit; however, the ripening date for `Dayton' was 10 Sept., late for a summer cultivar. Mark and M.26 EMLA produced similarsized trees, while M.27 EMLA produced very small trees. A significant cultivar × rootstock interaction resulted from `Dayton' trees being larger than `Williams' Pride' when both were on M.26, while both cultivars produced similar-sized trees on M.27 or Mark. Of the four cultivars in this trial, we consider `Redfree' to be the best summer DRC for commercial orchards, based upon ripening date, yield, and fruit quality. Mark rootstock was preferable to M.26 or M.27 for the cultivars in this trial, with the best tree growth and precocity.
J.R. Schupp and S.I. Koller
The growth, precocity, yield, and fruit size of `Liberty', `NY 75414-1', `NY 74828-12', and `NY 65707-19' on M.27 EMLA, M.26 EMLA, and Mark rootstocks, and `McShay' on M.26 EMLA and Mark, were compared. `Liberty', `McShay', and `NY 74828-12' trees were larger than `NY 75414-1', while `NY 65707-19' trees were the smallest. Among rootstocks, trees on Mark were larger than trees on M.26, while trees on M.27 were the smallest. There were no interactions between cultivar and rootstock on tree growth in this study. `NY 74828-12' produced the most flower clusters in the 3rd and 4th years of the study, and `NY 65707-19' the least. In 1993, trees on Mark had more flowers than those on M.26, while trees on M.27 had the fewest flower clusters. `Liberty', `NY 75414-1', and `NY 74828-12' produced higher cumulative yield than `McShay' and `NY 65707-19'. Trees on Mark had higher cumulative yield than M.26, while trees on M.27 produced the smallest yields. Fruit size was greatest for `NY 65707-19' and smallest for `NY 74828-12'. Trees on M.27 produced smaller-sized fruit than trees on M.26 or Mark. `NY 75414-1' had moderate vigor, high precocity, yield, and yield efficiency, with acceptable fruit size. `NY 74828-12' also performed well in this trial, but possesses Vm resistance to apple scab, not Vf, and is unlikely to be named. Based on tree vigor, percocity, yield, and fruit size, `Liberty' and `NY 75414-1' have the best potential for commercial production among DRCs in this trial. Mark rootstock produced the largest trees with the highest yields, and was superior to M.26 as a rootstock for the DRCs in this study.
H.E. Winzeler and J.R. Schupp
The coverage extent and intensity of apple blush are important factors in the evaluation of apple fruit quality for some cultivars. We analyzed blush coverage extent and intensity in the cultivar Honeycrisp to 1) define categories of marketable blush in terms relating to device-independent color measurements; 2) assess relationships among a modified anthocyanin index (AIm) calculated from spectral measurements, colorimetry (CO), and human judgment of apple blush intensity; 3) assess the efficacy of digital image analysis (DIA) of color-calibrated digital photography as a tool to measure blush coverage extent; and 4) explore differences between human judgment of blush coverage extent and DIA. AIm and CO were both effective in providing statistical categorical separation among five classes of apple blush in ‘Honeycrisp’: “non-blush,” “slight non-marketable blush,” “minimum quality marketable blush,” “clear marketable blush,” and “outstanding blush” as judged by human participants. The boundary between blush and non-blush was judged to be a hue angle less than 49.0 ± 3.1 hab in CIELAB L*Cab*hab color space and an AIm value greater than 4.3 ± 1.3 at α < 0.05. DIA was less sensitive and did not show statistically significant differences between “clear marketable blush” and “outstanding marketable blush,” although its use to distinguish the other categories was successful. All methods of analysis resulted in high agreement with respect to the blush/non-blush boundary (Cohen's kappa ≥ 0.897).
J.R. Schupp, M.M. Bates., and H.J. Brummer
`Empire' is a popular new apple with fruit growers in the northeastern United States, noted for producing small-sized fruit. To test the efficacy of chemical thinners and rootstocks for increasing fruit size of `Empire', three-tree plots containing trees on M.7 EMLA, MM. 111, and seedling rootstocks were chemically thinned at petal fall with 10 ppm NAA or 85 ppm 6 BA, applied as Accel. Both NAA and Accel reduced fruit set. Trees on M.7 EMLA had higher set than trees on seedling. Yield was highest on M.7 EMLA and lowest on seedling. Fruit diameter after final set in July was increased by both chemical thinners and was greater for both clonal rootstocks than for seedling. Fruit on seedling trees were delayed in maturity relative to the two clonal rootstocks. Accel increased the number of fruit 70 mm or greater in diameter, while NAA increased the number of fruit in the 64- to 69-mm-diameter class. Analysis of covariance with crop load suggested that the increase in fruit size associated with Accel was a direct effect rather than a secondary effect from thinning.
J.R. Schupp, S.I. Koller, and W.D. Hosmer
This study was undertaken to test the efficacy of a power duster for supplemental pollination of `McIntosh' apple trees, where lack of nearby pollinizing cultivars was thought to be a limiting factor to productivity. The pollen duster was ineffective in increasing fruit set, fruit size, or seed number in fruits on limbs that were covered with spun-bonded rowcover material prior to bloom. Applying supplemental pollen to open-pollinated `McIntosh' trees had no effect on fruit set, yield, fruit size, or seed number, regardless of pollen dose, timing, or number of applications. Dispersal of supplemental pollen with a power duster appears to be an inefficient method of pollinating apple trees.
John J. McCue, James R. Schupp, and Highmoor Farm
The growth and fruiting of 10-year-old `Mcintosh'/M.7 apple trees were compared under the following weed management systems: 1)untreated control; 2) herbicide spray (paraquat + oryzalin); 3) rotary tilling applied in May, June and July; 4) rotary tilling plus herbicide (oryzalin); 5) rotary tilling plus oats sown in August. All weed control methods increased tree growth compared to the untreated control over three years. Yield and fruit size were increased by the herbicide and the rotary tilled treatment. Rotary tilling plus herbicide increased yield but fruit size was larger than controls in 1990 only. Rotary tilling plus oats produced yield and fruit size equivalent to the control. In 1989 and 1990 rotary tilling alone provided less weed control compared to the herbicide treatment, while in July 1991, the reverse was true. Rotary tilling with herbicide and with oats have demonstrated weed control comparable to or better than the herbicide treatment except for the rotary tilled plus oats treatment in 1990. There were no differences among treatments in fruit color, maturity and percent soluble solids.