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‘Honeycrisp’ (Malus ×domestica) apples were harvested from a total of 17 mid-Atlantic orchards during 2018 and 2019 to verify a previously published bitter pit prediction model. As in the previous study, bitter pit incidence was associated with low calcium (Ca) levels and high ratios of nitrogen (N), potassium (K), and/or magnesium (Mg) to Ca in the fruit peel and excessive terminal shoot growth. The best two-variable model for predicting bitter pit developed with the 2018–19 data set contained boron (B) and the ratio of Mg to Ca (R2 = 0.83), which is different from previous models developed with data from three individual years (2015–17). When used to predict the bitter pit incidence of the 2018–19 data, our previous best model containing the average shoot length (SL) and the ratio of N to Ca underestimated the incidence of bitter pit. The model is probably biased because one or more important variables related to bitter pit have not yet been identified. However, the model is accurate enough to identify orchards with a low incidence of bitter pit.

In three experiments, diameters of apples representing 7% to 30% of the fruit on a tree were measured at ≈60 days after full bloom. Using previously published regression equations, the early-season fruit diameter values were used to estimate apple fruit weight at harvest (FWH). At harvest, all fruit on sample trees were weighed and the distributions of estimated FWH for fruit measured early in the season were compared with distributions of the actual FWH for whole trees. Actual FWH was normally distributed for only one of the three experiments. Although the estimated mean FWH averaged for the 10 trees was within 9% of the actual mean FWH for all three experiments, the distribution of estimated FWH differed significantly from the actual distribution for all three experiments. All fruit were then assigned to appropriate commercial fruit sizes or box counts (number of fruit/19.05 kg). Fruit size tended to peak on the same four box counts for the estimated and actual populations, but the estimated populations had too few fruits in the small- and large-size box counts. Using early-season estimates of FWH, commercial apple growers and packers can predict fairly accurately the percentage of the crop that will fall into the peak box counts, but a more accurate early-season estimate of the fruit size distribution will likely require measuring 50% of the fruit on a tree.

Canopies of ‘Gala’ and ‘Fuji’ trees, trained to the vertical axis, were divided into eight vertical sections, each representing 12.5% of the tree canopy. The diameter of all ‘Gala’ fruit and fruit weight for all ‘Fuji’ fruit were recorded for each canopy section. Fruit size from most canopy sections was normally distributed and distributions were similar for most sections. Therefore, fruit size distribution for a tree can be estimated by harvesting fruit from two sections of a tree, representing 25% of the canopy. For small trees in intensive plantings, with canopy diameters less than 2.0 m, average fruit diameter or fruit weight estimated from all fruit collected from 25% of the canopy may provide estimates within 7% of the true value.

Early-season fruit diameter measurements for ‘Gala’, ‘Fuji’, and ‘Honeycrisp’ apples in three orchards for 3 years were used to develop regression models to estimate fruit weight at harvest. Fruit weight at harvest was linearly related to fruit diameter 60 days after bloom, but intercepts and slopes were not homogeneous for all nine combinations of orchards and years for any of the cultivars. When the entire data set for a cultivar was used to develop a single predictive model, the model was biased and underpredicted fruit weight for small fruit and overpredicted fruit weight for large fruit. Adding the ratio of (fruit weight/fruit diameter) at 60 days after bloom to the model with fruit diameter at 60 days after bloom produced a less-biased model with improved coefficients of determination, and predicted values were more similar to the observed values. The (fruit weight/fruit diameter) ratio was positively related to cumulative growing degree days for the 60 days before the fruit were measured and tended to be lower in years when fruits were exposed to frosts. These multiple regression models can be used to develop tables with predicted fruit weights at harvest for varying combinations of fruit diameter and (fruit weight/fruit diameter) ratio 60 days after bloom.

During a 3-year study of bitter pit in commercial ‘Honeycrisp’ apple (Malus ×domestica) orchards, incidence was associated with low calcium (Ca) levels in fruit peel; high ratios of nitrogen (N), potassium (K), and/or magnesium (Mg) to Ca in fruit peel; excessive terminal shoot length; and low crop load. Peel N and Mg concentrations were negatively correlated and peel Ca concentration positively correlated with crop density (CD). Shoot length (SL) was not consistently correlated with peel N, Mg, or phosphorus (P) and was negatively correlated with only Ca. A two-variable model that included SL and the ratio of N to Ca explained more than 65% of bitter pit incidence. The model has implications for best management of the cultivar in the field and during storage.

Pruning is the cutting away of vegetation from plants for horticultural purposes. Pruning is known to reduce apple tree size, increase fruit size and quality, and decrease yield. Methods for studying the effects of varying degrees of severity of pruning on a whole-tree basis have used qualitative descriptions of treatments rather than repeatable whole-tree quantitative metrics. In this study, we introduce a pruning severity index calculated from the sum of the cross-sectional area of all branches on a tree at 2.5 cm from their union to the central leader divided by the cross-sectional area of its central leader at 30 cm from the graft union. This limb to trunk ratio (LTR) was then modified by successively removing the largest branches of ‘Buckeye Gala’ to achieve six severity levels ranging from LTR 0.5 to LTR 1.75, with lower values representing more extreme pruning with less whole-tree limb area relative to trunk area. Pruning treatments were applied for three consecutive years and tree growth and cropping responses were observed for the first 2 years. With increasing pruning severity the following characteristics increased after seasonal growth: number of renewal limbs, number of shoots, shoot length, number of shoot leaves, shoot leaf area, final fruit set, fruit size, yield of large fruit, crop value from large fruit, soluble solids, and titratable acidity. The following characteristics decreased: limb age, number of secondary limbs, number of spurs, number of spur leaves, spur leaf area, the ratio of spur leaf area to shoot leaf area, fruit count per tree, yield, yield efficiency, crop value from small fruit, overall crop value, and sugar:acid ratio. The LTR provides a measurable way to define and create different levels of pruning severity and achieve consistent outcomes. This allows a greater degree of accuracy and precision to dormant pruning of tall spindle apple trees. The use of the LTR to establish the level of pruning severity allows the orchard manager to set crop load potential through regulation of the canopy bearing surface. This metric is also a necessary step in the development of autonomous pruning systems.

A bicultural team of Penn State Extension professionals assessed educational method and learning style preferences of Hispanic/Latino stakeholders who aspire to be next generation specialty crop growers and specialized horticultural managers. During 2014–16, team members conducted and evaluated bilingual programs in various formats, including in-depth workshops, model demonstration plots, on-farm trainings and tours, fact sheets and field guides, and videos. Postprogram surveys indicated formats that provided opportunities for active learning of research-based information applicable to participant operations were most successful. Purposive surveys and interviews identified further ways to adapt extension outreach and education for next generation growers. The top-rated methods of learning for Hispanic/Latino growers were on-farm demonstrations and study circles, tours of other growers’ farms, self-paced on-line courses and videos, and interactive workshops. Factors Hispanic/Latino grower survey respondents felt limited them from participating in educational activities or using extension resources were timing of program, cost, and location. Survey participants suggested extension might improve education and engagement with Hispanic/Latino growers by increasing the use of social media in Spanish, holding educational programs specifically for Latino farmers to increase networking opportunities, and holding educational events at the farms of Latino growers.

Apple harvest depends on a large seasonal workforce, and decreasing availability of agricultural employees, increasing labor costs, and occupational injuries are creating challenges for apple harvest activities. Researchers at The Pennsylvania State University developed a low-cost apple harvest-assist unit to improve apple harvest efficiency. The unit performed reliably during field tests. Apple bruising incidence, however, was extremely high with the initial design. This was a major problem for this unit, which targeted fresh market apples. This study focused on identifying reasons for apple bruising, and designing and testing a new speed-reduction brush mechanism for distributing the apples into the bin. Field tests demonstrated that 98.50% and 1.50% of ‘Fuji’ apples harvested by this unit with the speed-reduction brush mechanism mounted were graded as “Extra Fancy” and “Fancy”, respectively. The satisfactory experimental results demonstrated the commercialization potential for this low-cost apple harvest-assist unit utilizing the brush speed-reduction mechanism.

Harvest is one of the most challenging production tasks in apple production. It is a labor-intensive operation, and mechanization has been slow in development for a myriad of reasons. With increasing labor costs and decreasing availability of harvest employees, researchers have been focusing on mechanical apple harvest technologies. Studies on semi-automatic harvesters, harvest robots, and harvest-assist platforms target development of mechanical apple harvesting. Semi-automatic harvesters for fresh market apples have not been commercialized due to unacceptably high incidence of apple bruising. Harvest robots have not been commercialized due to their high costs and low efficiency. Apple harvest-assist platforms are a technology that has the potential to be more widely commercialized based on the current research.

The U.S. apple industry is facing difficulties because apple production costs have been continuously increasing. Three factors contribute to this situation: close dependence on a large seasonal workforce, increasing labor costs, and decreasing availability of agricultural employees. Apple harvest is the most labor-intensive operation during the production season. An economical apple harvest-assist unit prototype targeting fresh market apples was designed and field tested, aimed at increasing harvest efficiency, reducing harvest-related injuries, and increasing the potential labor pool through decreased working strength requirements. This harvest-assist unit focused on apples in the top of the canopy, which typically require use of ladders for conventional harvest. The unit was field tested for two years, with the first year focusing on identifying the components that caused apple bruising, and the second year focusing on identifying the performance of this unit. After being identified as the major component causing apple bruising, the distributor (a rotating disk used to distribute apples evenly in the bin) was improved and then tested in the second-year experiment. Apple downgrade incidence was reduced to 0% using an optimized distributor rotation speed of 28 rpm. For the apples located in the upper portion of the trees, the harvest-assist unit increased apple harvest efficiency (apples picked per second) by 95% compared with the conventional apple harvest method using ladders.

The objective of this investigation was to develop and test an automated selective fruit-thinning system for blossom removal in peach tree orchards. The proposed system needed to visualize the tree fruit canopy, discriminate targets (blossoms), mechanically reach the canopy from a stable platform, and remove unwanted targets. The system consisted of kinematic targeting and heuristic programming, a robotic arm, and a pomologically designed end-effector. A quarter-scale robotic arm based on a Fanuc M-16iL manipulator model and rotating brush end-effector were designed and constructed for this study. The normal and tangential force requirements to remove a peach blossom from a shoot were also evaluated. The resultant blossom force tests yielded a range of 0.44 to 0.57 N for the normal force and 0.49 to 0.71 N for the tangential force. The precision and accuracy of the robotic arm and end-effector placement were then examined. A kinematic positioning test for the robotic arm consisting of 120 repetitions fell within the first standard deviation of a proposed ±2.54 cm precision standard. With a confidence level of 95% and a margin of error of ±8.96%, the robotic arm had a consistent range of -1.26 cm to +1.57 cm vector magnitude per target location. For the end-effector positioning test, the brushes reached the proposed ±2.54 cm target area 100% of the time. The deviation from the target to the center of the brushes was within the first standard deviation with a confidence level of 95% and a margin of error of ±10.33%, and the end-effector brushes had a consistent range of -2.97 cm to +3.04 cm per target location. The selective spatial thinning heuristic algorithm was also tested. The heuristic test consisted of a series of branches that varied in length from 10, 15, and 20 cm spanwise across the branch, with three artificial blossoms placed every 5 cm. The end-effector successfully removed the unwanted blossom in each case.

‘Honeycrisp’ apple fruit are highly susceptible to development of soft scald and bitter pit during storage. However, the commercial postharvest treatment of conditioning fruit at 10 °C for 7 d before storage at 3 °C to reduce soft scald development can increase bitter pit incidence. Prediction of these physiological disorders would enable storage operators to modify management techniques to reduce fruit losses due to both disorders. To develop prediction tools, harvest indices and mineral concentrations of fruit were analyzed from orchard blocks in Pennsylvania (PA) for three years, the Hudson Valley region (HV) for four years, the Champlain region for two years, and Western New York (WNY) for five years. Fruit were stored at 3 °C, without or with conditioning, and stored for 2 - 5 months in 2013- 2017. Fruit were also stored at 0.5 °C without or with conditioning in 2013, 2015, 2016. Multivariate analysis described significant relationships that were different for unconditioned and conditioned fruit. In unconditioned fruit, bitter pit incidence was negatively correlated with increasing internal ethylene concentration (IEC) and starch pattern indices (lower starch content), positively with higher chlorophyll content as indicated by the index of absorbance difference and with all minerals except N, as well as mineral ratios. In conditioned fruit, bitter pit incidence was correlated negatively with IEC, Ca, and positively with firmness, and all mineral ratios. Soft scald incidence in fruit stored at 0.5 °C was positively correlated with IEC and firmness, and all fruit mineral ratios except N/Ca and P/Ca, and negatively with Ca and Mg. For conditioned and unconditioned fruit stored at 3 °C, harvest indices predicted 27-28 % and 21-26 % bitter pit, respectively, while minerals and mineral ratios predicted 22-55 % and 18-54 % bitter pit, respectively. Harvest indices predicted 29-57 % soft scald, while minerals and mineral ratios predicted 29-49 for % soft scald for fruit stored at 0.5 °C. Correlations of bitter pit against P, K, and Mg were higher, and Ca and all mineral ratios lower, in conditioned fruit stored at 3 °C as opposed to those stored unconditioned at 3 °C. Nonlinear iterative partial least square algorithms based on variable importance plots vs coefficients showed that the regression of determination was affected by postharvest treatment in relation to harvest indices, minerals and their ratios. A negative correlation of bitter pit incidence against soft scald incidence was found for a region with high bitter pit and soft scald development.

Increasing labor costs and changes in labor forces have prompted an increased demand for automation in specialty crop production. Implementation of technological innovations in the agricultural sector tends to be slow, thus this study investigated motivations and perceptions of technology. Using qualitative interviewing and analysis, this study used a diffusion of innovations framework to gain insight into what channels of communications impacted planned adoption rates and what aspects of technology influence the decision-making process. Interview participants emphasized the inevitability of implementing new technologies while considering the capital investment of more complex technology, changes in labor management to integrate technology, applicability of technology to current practices, and trust in technology designers.

Peach (Prunus persica L. Batsch) thinning is a costly and time-consuming but necessary practice to produce a crop of marketable size fruit. A number of mechanical devices and methods have been developed and evaluated to reduce the cost and time required for hand thinning peach. This report provides additional evidence that a Darwin string thinner can effectively thin peach at bloom and a spiked drum shaker can thin at bloom or at the green fruit (pit hardening) stage. Five trials were conducted over 2 years in grower orchards with trees trained to a perpendicular V system. A Darwin string thinner at 60% to 80% full bloom (FB) reduced crop load (fruit/cm2 limb cross-sectional area) on scaffold limbs by 21% to 50% compared with a hand-thinned control. At the 60% FB stage, a USDA-designed double-spiked drum shaker reduced crop load by 27% and in another trial, a USDA prototype single-drum shaker reduced crop load by 9%. Across all trials, the spiked drum shakers (single or double units) removed an average of 37% of the green fruit. All mechanical devices reduced the time required for follow-up hand thinning. Follow-up hand-thinning costs (US$/ha) were reduced an average of 27% by mechanical thinning devices over hand-thinned control trees. Fruit size was increased over hand-thinned controls by mechanical thinning in most, but not all, trials. A combined treatment of the Darwin string thinner at bloom followed by a drum shaker (single or double unit) at the green fruit stage produced the greatest net economic impact in a number of the trials. Despite overthinning in some trials, the mechanical thinning devices described provide a potential alternative to hand thinning alone in peach production.

Advances in horticultural production technology are often hindered by slow grower adoption. Low adoption rates are largely the product of skepticism, which can lead to weaknesses in the commercialization process and affect future research and product development. To better understand industry concerns and design effective outreach methods, an information technology survey was designed as part of the U.S. Department of Agriculture Specialty Crop Research Initiative project titled Comprehensive Automation for Specialty Crops (CASC). This study outlines the survey results from 111 participants at tree fruit meetings in the Pacific northwestern and eastern United States in 2009. Many of the misgivings about new automated technologies, such as equipment cost and reliability of harvest assist, sensor systems, and fully automated harvest machinery, were consistent across the country. Subtle differences appeared between the eastern U.S. and Pacific northwestern U.S. responses, including justifiable equipment price points and irrigation and pest concerns; these are likely attributable to regional differences in climate, operation size and scale, and marketing strategies. These survey data will help the project team better address grower concerns and uncertainty on a regional and national level, thereby improving adoption speed and rates after CASC-developed technologies are rolled out.

A unique dry bin filler for apples using a sequenced tray was developed to reduce bruising in packing operations. Research and commercial trials in West Virginia, Pennsylvania, and Washington State demonstrated the ability to fill bins evenly and with low damage. Cultivars with different bruising susceptibility ('Pink Lady,' 'Golden Delicious,' 'McIntosh,' 'Mutsu,' 'Delicious,' and 'Fuji') were used to test the bin filler in research trials and commercial assessments. Fruit that were downgraded from U.S. Extra Fancy grade after handling by the bin filler were 1.7%, 1.4%, and 2.9% at each test location. The filler was shown to produce less than 5% bruising on fruit and to have the ability to operate in commercial locations.

The apple industry is currently facing difficulties because apple production costs have been increasing continuously. Three factors contribute to this situation: close dependence on a large seasonal workforce, increasing labor cost, and decreasing availability of agricultural employees. To help the apple industry survive and thrive, a new apple harvest-assist unit has been designed and fabricated. Cost of the unit is a factor that is being considered during the design/fabrication of the new apple harvest-assist unit, as the final goal for this research is to commercialize the device. Lab and field tests were conducted on the unit during fall and winter of 2013. Field tests demonstrated that this low-cost apple harvest-assist device worked very well in the field. Major components causing apple bruising for this device were identified as distributor and collection bin. Tests also showed that the apple mass did not affect bruising area. Obtained results provided some critical information required for optimization of this apple harvest-assist unit.

We compared conventional and alternative systems for the establishment of apple trees on a replicated, whole-orchard scale. The alternative system consisted of a K-31 fescue sod rotation followed by planting of trees directly into sod that had been kitted with herbicide. The conventional system consisted of a standard corn rotation, accompanied by application of fertilizer and nematicide. Orchard floor management in the three years following tree planting was based on the use of both pre-and post-emergence herbicides in the conventional system and only contact herbicide in the alternative system. The study documented tree growth, pest incidence, and nitrate mobility in the two systems. The alternative system compared favorably with the conventional system for the growth and establishment of four apple cultivars. Many advantages accompanied the killed sod system, including less subsurface leaching ofnitrate-N and lower costs (largely from decreased herbicide use). The alternative system provided an economical alternative to the problem of soil organic matter depletion in conventional orchard soils without requiring increased use of commercial fertilizers. Grower concerns regarding increased potential for vole damage and poor initial tree growth were unsubstantiated.

Three growth suppression treatments were compared during 1991 to 1993 on `Stayman' apple (Malus domestica Borkh.) trees grown in the T-trellis and the MIA trellis systems. All treatments—root pruning, K-31 fescue (Festuca arundinacea Schreb.), and K-31 fescue plus root pruning—suppressed tree growth compared to the nontreated control, but results were inconsistent between years and systems. Sod or sod plus root pruning reduced terminal shoot length in both systems in 2 out of 3 years. Root pruning decreased shoot length in the T-trellis in 1992. Sod decreased trunk cross-sectional area in the T-trellis in 1993. Treatments did not affect 3-year average yield efficiency but did appear to increase biennial bearing. Sod, with or without root pruning, decreased fruit cracking in the T-trellis 69% and 42%, respectively, in 1992, and sod plus root pruning decreased cracking in the MIA trellis 50%. Sod reduced fruit diameter in the T-trellis in 1992. Secondary effects of growth suppression treatments included increased light penetration and improved fruit color. Sod decreased leaf N and Mg and increased leaf P, K, and Cu. The Oct. 1993 stem water potential gradient from root to canopy was more negative in the sod plus root pruning treatment, and the osmotic potential of rootsucker leaves in the combination treatment was greater than in the control, indicating that sod plus root pruning alters the distribution of water within a fruit tree.

Integrated whole farm management systems offer the potential to reduce impacts on the environment and human health by reducing inputs of petrochemicals while increasing net income to the fruit industry through reduced costs. This article reports on the rotation phase of orchard establishment focusing on integration of an alternative rotation crop system (tall fescue) with a conventional orchard establishment practice (m + nematicide). A 5.6-ha (14-acre)orchard has been established at the West Vuginia University Experiment Fann, Keameysville, WV. The site has been divided into six 0.8-ha main plots with each plot randomly assigned one of two rotation treatments. Comparisons between rotation treatments included soil organic matter and fertility, populations of plant pathogenic nematodes, nematode biological control activity, and an economic analysis. When compared with the conventional corn rotation, plots rotated with fescue exhibited increased numbers of nematode biological control organisms, higher soil ...

A study was conducted to quantify the effects of rootstock and training system on C allocation in apple. Dry-matter distribution was determined at harvest in 5-year-old `Golden Delicious' apple (Malus domestica Borkh.) trees on four rootstocks (MM.111 EMLA, M.7a, M.26 EMLA, and M.9 EMLA) and in three training systems (three-wire palmette, free-standing central leader, and nonpruned). Mobilizable carbohydrate content was determined at harvest and leaf fall in trees from the same planting on MM.111 EMLA and M.9 EMLA in all three training systems. Training system effects interacted with rootstock effects in dry weights of branches and of fruit. Nonpruned system shoot and fruit dry weights reflected known rootstock vigor; whereas, pruned system (three-wire and central leader) shoot dry weights were greatest and fruit dry weights were lowest in trees on M.7a. Rootstock affected the partitioning of dry matter between above- and below-ground tree components, with MM.111 EMLA accumulating significantly more dry matter in the root system than trees on the other rootstocks. Trees in the central leader and the three-wire palmette systems partitioned more dry weight into nonbearing 1-year shoots than trees in the nonpruned system. Root starch content at harvest was greater in trees on MM.111 EMLA than on M.9 EMLA, and root sucrose and sorbitol were less in trees on MM.111 EMLA compared to M.9 EMLA. At leaf fall, starch in young roots was equal in trees on both rootstocks, and sorbitol again was lower in trees on MM.111 EMLA. Harvest starch content of roots, shoots, and branches was lower in nonpruned than in pruned trees. At leaf fall, root, shoot, and branch starch content increased in nonpruned and central leader-trained trees but did not increase in three-wire palmette-trained trees.

Hand thinning is a labor-intensive and expensive peach production practice. Mechanical thinning has been shown to be an economical method of reducing thinning cost. However, current mechanical thinning systems applied to perpendicular V systems require the operator to constantly steer the tractor to maintain engagement. This paper presents a system using a LIDAR to sense the canopy and automatically control the position of a modified Darwin string thinner position to maintain engagement. We demonstrate that the automated system is approximately as good as a human at maintaining canopy engagement by presenting blossom removal counts, and suggest that this may be an economically viable method of augmenting mechanical thinning.

Bin filling remains among the most challenging operations of apple harvest. The current standard practice is careful release of fruit from the bottom of a picking bag while sweeping the across the top layer of apples already in the bin to distribute the fruit with minimal bruising. This process is time consuming and still prone to damage the fruit. In this paper we describe two new devices that show promise for increasing speed and reducing bruising in passive bin filling. The first distribution is the energy absorbing grate for apple distribution and bin filling in which apples are dumped through a network of elastic bands holding energy absorbing foam shapes. The vibration of the elastic bands creates a fluidized bed effect that allows apples to pass through the device while reducing their speed so that bruising is nearly eliminated. The second is the pneumatic self-adjusting bin filler, in which alternate inflation and deflation of adjacent cylindrical bladders causes the device to climb up the rising pile of apples in the bin filler. The bladders also serve as to absorb the energy of the falling apples. We will present the design process, the results of laboratory and field tests, lessons learned, and future plans.

Studies were conducted on peach (Prunus persica (L.) Batsch) during 1988 to 1990 to test the performance of a tree-width rope-curtain bloom thinner and a rotating rope-curtain thinner. Six trips over the tree canopy were required with the tree-width rope curtain, and only one trip was required with the rotating curtain to thin to a spacing of about one flower per 9 cm of fruiting shoot length. Based on the number of flowers per square centimeter of branch cross-sectional area (CSA) immediately following thinning and the number of fruit per square centimeter of CSA following June drop, rope-curtain thinning was equal to hand-thinning at full bloom (FB). Rope-curtain thinning reduced hand-thinning time by 40% and increased harvest fruit weight by 10% to 20%. Research on various modifications in tree training/pruning indicated that performance of the mechanical thinner was negatively correlated with shoot density. Thinning was maximum on open-center-t rained trees on which detailed pruning had been con- ducted to eliminate overlapping shoots. Thinning peaches at bloom increases fruit size, flower bud formation, and, in general, revenue to the grower (Baugher et al., 1988; Byers, 1989; Byers and Lyons, 1985; Byers et al., 1990; Johnson and Handley, 1989). Although the standard com- mercial practice still is to thin peaches by hand at 40 to 60 days after full bloom (DAFB), hand-thinning at FB is becoming more common (Myers, 1986). Peach orchard profits can be further increased if hand bloom thinning is replaced by chemical or mechanical thinning. Byers and Lyons (1985) have shown that desiccating chemicals can be successfully used at FB to thin peaches; however, commercial registration of these chemicals remains questionable. Preliminary studies on mechanical bloom thinning with a rope curtain (Baugher et al., 1988) or a high- pressure water stream (Byers, 1989) show promise, but the tech- niques need refinement. Rope thinning was initially tested in West Virginia in 1987 (Baugher et al., 1988). Our research demonstrated that maxi- mum thinning occurred when 80% to 100% of the blossoms were open and the tractor operated at 3.2 km·h -1 . The most effective treatments removed 45% to 60% of the blossoms and reduced follow-up hand-thinning time by 30%. Disadvantages of the 1987 test unit were: 1) multiple trips over the tree were required and 2) fewer flowers were removed in the lower third than in the upper part of the canopy. Studies were conducted in 1988 to 1990 to test modifications of the rope-curtain thinner and also of tree training for potential effects on thinning. The objectives were to reduce the number of trips through the orchard, improve uniformity of thinning, reduce labor, and increase fruit size.

The characteristics of l-year-old vegetative spurs growing on 2-year-old branches were measured on 28 ‘Delicious’ apple (Malus domestica Borkh.) strains growing on M.7 rootstocks at Clarksville, Mich., and on 23 strains of ‘Delicious’ on M.7a rootstocks at Kearneysville, W.Va. Spur-type strains typically had densities >20 to 21 spurs/m, and high spur leaf numbers, leaf areas per spur, leaf areas per leaf, and terminal bud diameters, whereas values for standard strains were generally lower. However, for most spur quality characteristics, there was a continuous range of values between the extremes rather than any distinct grouping into either spur or standard type. At both sites, spur density was significantly and positively correlated with yield efficiency. In a related study, the spur characteristics of ‘Starkspur Supreme’ were measured on nine rootstocks: M.7 EMLA, M.9 EMLA, M.26 EMLA, M.27 EMLA, M.9, MAC 9, MAC 24, OAR 1, and Ottawa 3. Spur leaf number and spur leaf area were both high with vigorous rootstocks, whereas spur density was low. The rootstocks MAC 9, M.9, and M.9 EMLA had the highest yield efficiencies. A feature of red apple cultivars in general, and of ‘Delicious’ in particular, is the availability of many different strains from commercial nurseries (Tukey and Ballard, 1969a). Most ‘Delicious’ strains have been selected primarily either for some specific fruit characteristic (mainly color and shape) or for a particular type of growth and related spur-bearing habit that is predominantly either a spur type or standard form (Fisher and Ketchie, 1981; Tukey and Ballard, 1969b). However, while fruit characteristics are well known and definable (Crassweller et al., 1985; Fisher and Ketchie, 1981; Ingle, 1972; Lord et al., 1980), few data are available on the yield performance of the different strains or on the relative performance of strains within and among apple-producing regions (Dozier et al., 1984; Ferree et al., 1975; Ketchie, 1984, 1987; Lord et al., 1980; Rom and Ferree, 1984). Therefore, the selection of the most appropriate and highest-yielding strains for a particular region is not possible unless either comparative regional trials are carried out (Ketchie, 1987) or indices can be identified that would allow a prediction to be made of relative performance. An obvious difference in the growth characteristics of various ‘Delicious’ strains is the degree of spur-bearing habit. Spur leaves are critically important for fruit development (Ferree and Palmer, 1982), and differences in spur habit and form may, therefore, influence fruit yield and the distribution of fruit on a tree. Before bloom, spur leaves constitute the major leaf area on a Received for publication 8 June 1989. Salaries and research support provided nd federal funds appropriated to the Ohio Agricultural Research and ent Center, The Ohio State Univ. Journal Article no. 18-89. The cost ing this paper was defrayed in part by the payment of page charges. stal regulations, this paper therefore must be hereby marked adverolely to indicate this fact. address: Plant Physiology Division, DSIR, Private Baa, Palmerston ew Zealand. ddress: Highmoor Farm, Univ. of Maine, PO Box 178, Monmouth, 9. tree and provide the majority of photosynthate available for early fruit growth and development (Hansen, 1971). During fruit set and the cell division phase of fruit growth, spur leaves play a major role in determining fruit size, shape, and fruit calcium concentration (Ferree and Palmer, 1982). The removal of spur leaves before and during bloom reduces fruit set (Dalbro, 1966), while a certain minimum spur leaf area is necessary for flower bud formation (Harley et al., 1942). Differences among apple cultivars for spur diameter, flower number, spur leaf number, area, and individual spur leaf size have been reported, and total spur leaf area or average spur leaf size has been related to tree productivity, yield efficiency, and yield variation (Rom and Ferree, 1984). The objective of this study was to evaluate these relationships on various commercially designated spur and standard ‘Delicious’ strains growing in two locations. In addition, the influence of rootstock on spur quality, tree size, and yield of ‘Starkspur Supreme Delicious’ was investigated on trees planted at the Ohio Agricultural Research and Development Center (OARDC), Wooster. (Throughout the manuscript, the word ‘Delicious’ has been deleted from each strain name to avoid unnecessary repetition.) Materials and Methods Twenty-eight ‘Delicious’ strains were evaluated at the Michigan State Univ. Clarksville Horticultural Research Station (Table 1). The trees were established in 1980 in a planting 18 trees long and 21 rows wide, with each strain represented by one tree in each of six blocks. All of the strains studied were planted on M.7 EMLA rootstock. An equal number of trees on MM.111 EMLA rootstock were randomly distributed among the study trees, and four individual trees of ‘Idared’ were included in each block as pollenizers. Trees of similar age and size surrounded the planting. The within/between row spacing was 3.65 × 5.5 m. The trees were part of a cooperative research program to J. Amer. Soc. Hort. Sci. 115(3):348-356. 1990. Table 1. ‘Delicious’ strains studied, name of the supplying nursery, plant patent number, growth type, and location of study site. Strain Nursery U.S. plant Growth Study company patent type site

A 2-year study was designed to test the effect of four growth-suppressing treatments on the incidence of nectarine [Prunus persica (L.) Batsch] pox, nectarine fruit quality, and the growth and nutritional status of nectarine trees. Root pruning was the only treatment that significantly reduced the incidence of nectarine pox. The percentage of red surface was increased by root pruning, foliar-applied paclobutrazol, and girdling. Root pruning and paclobutrazol suppressed extension shoot growth. Root pruning decreased fruit N, P, K, Mg, Mu, Fe, B, and Zn levels and increased fruit Ca. Results of the study support earlier observations that nectarine pox is associated with excessive shoot growth, excessive levels of fruit N and K, and low levels of fruit Ca. Chemical name used: Beta-[(4-chlorophenyl) methyl] -alpha-(1,1-dimethylethyl)-l-H-1,2,4 -triazole-l-ethanol (paclobutrazol).

Fruit of 10 `Delicious' apple (Malus domestica Borkh.) strains were harvested 149 days after full bloom in 1988. Fruit color was measured at four locations on each fruit at the midpoint between the stem and calyx end with a Minolta CR-200b portable tristimulus calorimeter. Anthocyanin content of corresponding skin disks was determined spectrophotometrically. Significant differences existed among strains in both the amount and distribution of anthocyanin around the fruit. High-coloring strains had a significantly higher anthocyanin concentration at both the blushed and the nonblushed surface when compared to low-coloring strains. A linear regression of anthocyanin content on the ratio of (a*/b*)2 provided an R2 = 0.59; precision was enhanced by using a separate equation for each strain (R2 = 0.80). Regressing log (anthocyanin) on L* using two linear splines yielded an R2 = 0.78. These relationships allow the use of a portable calorimeter for rapid, nondestructive estimation of fruit anthocyanin content in situ.

Photosynthesis, light (PAR) and transpiration were measured with an ADC portable infrared gas analyzer on apples and grapes. Measurements were taken on north and south sides of the rows, in the morning and afternoon, on sun and shade leaves, and with the leaf chamber in a horizontal position and in a natural leaf orientation position. Measurements were made on three cloudless days in August 1990 and 1991. Subsequently, fruit adjacent to sampled leaves were harvested and soluble solids determined. Sampled leaves were then harvested and leaf areas and dry weights measured. Correlation coefficients of variables were then subjected to analysis of variance to determine which techniques gave the best correlations. Grapes and apples responded differently. For grapes, soluble solids were most closely correlated to light and photosynthesis measurements when measured on south side shade leaves, while with apples, blush side soluble solids were best correlated with measurements on south side sun leaves in the afternoon. Specific leaf weight was best correlated to photosynthesis and light with grapes when measured on north side sun leaves and with apples when measured on the south side in the morning.

“Nectarine pox” is a disorder that reduces packout of commercially grown nectarines [Prunus persica (L.) Batsch Nucipersica (Schneid)]. Although accounts of the occurrence of nectarine pox are widespread across fruit growing regions and cultivars, we found no studies describing it in the literature. The disorder is characterized by superficial warty outgrowths (Fig. 1) and, in some years, may occur on 20% to 80% of the fruit in an orchard block. Suggested causal agents include low levels of B or a virus (S. Johnson, personal communication). The expression of the disorder follows a trend similar to that of cork spot on apple. Nectarine pox is not observed every year in an orchard; it tends to be most severe when the crop load is light, shoot growth is excessive, N, K, and/or Mg levels are excessive and Ca and/or B levels are low. We have studied nectarine pox in West Virginia in a block of ‘Firebrite’ nectarines since 1984. Symptoms initially are observed 40 days after anthesis, sometimes as a pale white or light-colored circular spot 0.5 to 1.0 mm in diameter but more often as a slightly raised area similar in color and surface texture to the surrounding epidermal tissue. At this stage the

The objective of this study was to determine the relationship between temperature and color development in 3 strains of Red Delicious apple (Malus domestica Borkh). The strains `Scarlett Spur', `Ultrastripe' and `Starkrimson' were chosen based on variation in coloration. Chromaticity values (L* a* b*) were measured with a Minolta CR-200b calorimeter on 5 tagged apples on each of 4 trees of each strain. Measurements were made at approximately the same location on each fruit 23 times from July 11 through September 25, 1989. Differences in a*/b* ratio among strains were observed as early as the first sampling date; with `Scarlet Spur' having the highest ratio and `Starkrimson' the lowest. These differences were maintained for most the growing season. Temperature below 21C tended to enhance color development, whereas temperature above 21C reduced coloration. Temperature affected all 3 strains similarly.