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Adolfo Rosati, Andrea Paoletti, Raeed Al Hariri, Alessio Morelli, and Franco Famiani

dwarfing rootstocks ( Avery, 1970 ; Preston, 1958 ) and in some cases, the only mechanism ( Lliso et al., 2004 ), although in other cases, it is probably not the only one. In fact, defruiting apple trees on dwarfing rootstocks allows tree vigor to increase

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Warren Micke, Mark Freeman, Bob Beede, Lonnie Hendricks, and Jim Yeager

Some precocious almond varieties often produce little vegetative growth once they reach full maturity. A pruning trial was established using 11 year old `Harvey' trees that were healthy but making little or no new growth. The four treatments were: 1) severe heading or dehorning trees to six foot in height (first year only), 2) heading one third of the tree for three years, 3) making 20 small heading cuts all over the tree each year, and 4) normal thinning cuts (or control). All heading treatments caused more shoot growth than did the conventional thinning cuts (or control). The dehorning treatment (#1) responded with the most vigorous growth but much lower yields during the next two years compared to the control (#4). Yields were comparable between the two treatments during years three to five however. The heading treatments #2 and #3 had comparable yields with the control by the second year. They also showed more shoot growth. Tree yields from treatment #2 tended to lag below treatment #3 and the control, even though they were statistically the same. This trend may indicate that three years of moderately severe pruning is too much. Treatment #3 may be the best technique for invigorating healthy low vigor trees while minimizing yield losses, but will be the most expensive.

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L.P. Berkett, M.E. Garcia, J. Clements, and G. Neff

Apple scab, a fungal disease caused by Venturia inaequalis, is considered the most important disease of apple worldwide. The disease can be devastating, causing reduction in yield or making the apples unfit for the market. Currently, the production of marketable fruit from scab susceptible cultivars depends on the repeated applications of fungicides. Scab-resistant apple cultivars, which are genetically immune to apple scab, can offer a biological alternative to fungicide use. `Liberty,' was bred for immunity to apple scab; however, it is not immune to other apple diseases and pests. Research has been conducted during a 3-year project (1996–1998) to determine whether reduced fungicide programs adversely affect overall tree vigor, productivity, and fruit quality. Data collected include tree vigor (TCSA and time of leaf abscission), tree productivity (YE), and fruit quality (fruit firmness and disorders during storage). Results indicate no significant differences between the two treatments (reduced fungicide and no fungicide application) in most of the parameters measured. Based on fruit that were harvested and graded to commercial standards, the estimated gross monetary value of the crop does not show difference between treatments. These results could translate into an economic advantage for growers when one factors in the savings in fungicide purchases. In addition, there are also health and environmental advantages to reduced fungicide usage.

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Kuo-Tan Li, Jim Syvertsen, and Jacqueline Burns

The shedding of leaves, branches, flowers, and young fruit; scuffing of bark; and exposed roots that are caused by trunk or canopy shakers during harvest appears to be unavoidable, but generally does not reduce long-term yields. Nonetheless, such visible injuries have limited the widespread adoption of mechanical harvesting in Florida's citrus industry. We determined if such physical injuries caused by a properly operated trunk shaker resulted in any physiological injures or any consequent decline in vigor and productivity of well-managed, healthy citrus trees. We continuously monitored various physiological indexes in mature `Hamlin' and `Valencia' orange trees annually harvested by hand or by a linear-type trunk shaker with various shaking durations. Trunk shaking did not reduce return bloom, fruit set, young fruit growth, or canopy and root growth. There was a correlation between the seasonal timing of a simulated bark injury and recovery from the injury. Although some root exposure was frequently observed during trunk shaking, leaf water relations and fine root growth were unaffected. There was no difference in leaf dry weight per area and leaf nitrogen among treatments. Mechanical and hand harvesting in late season `Valencia' during full bloom removed similar amounts of flowers. However, immature fruit were removed by trunk shaking when `Valencia' were harvested after mid-May, and the number of young fruit removal increased with shaking duration and fruit size. The loss of young fruit for the next crop remains a major problem of mechanical harvesting in late harvest `Valencia'.

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C.S. Walsh, F.J. Allnutt, G.R Welsh, and R.H. Zimmerman

A planting to compare budded apple trees (M7a, Ml11) and tissue-culture-(TC) propagated trees was established in 1985. `Golden Delicious' and `Gala' trees were more productive than other cultivars and appeared better-suited to micropropagation. High cumulative yields per tree were harvested regardless of rootstock. `McIntosh', `Delicious', `Mutsu', and `MacSpur' trees were less precocious and more responsive to size-controlling rootstocks. To control tree size prior to bearing and minimize propagation time, trees were set as containerized transplants in a subsequent trial begun in 1986. Small containerized trees were set directly into the orchard. Setting trees in this manner has restricted tree size without delaying bearing. `Oregon Spur II' trees and `Empire' trees are now about 4 m tall. Trees have wide branch angles and numerous spurs. To further control tree size, trees were root-pruned with a Vermeer tree spade in 1991. In the year following, treated trees flowered profusely but did not fruit. Since then, cropping has controlled tree size. Ten years ex vitro `Granny Smith', `Oregon Spur II', and `Empire' trees can be managed without ladders. The goals of this study were: 1) to avoid “short life” problems and 2) develop a management scheme that would allow rapid entry of “bioengineered” cultivars into commercial orchards. Based on our research, selecting precocious cultivars or spur-type clones, in combination with transplanting 3 to 4 months ex vitro and root pruning show promise toward accomplishing these goals.

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Laura J. Lehman, Eric Young, and C.R. Unrath

Spur-type or nonspur `Delicious' apple scions on either Malus domestica Borkh. (seedling) or M.26 rootstocks received paclobutrazol foliar sprays in one or two `consecutive years or a soil drench in the year of planting. For each scion, total shoot, root shank, and tree dry weights measured in the 3rd year after planting were suppressed by all treatments. Trees on M.26 put less dry weight into rootstock wood after foliar sprays, but trees on seedling were not similarly affected. No treatment influenced fibrous root dry weight of the spur-type scion on seedling, while all treatments suppressed dry-weight gain of the same scion on M.26. All trees had higher root: shoot ratios and blossom densities 3 years after the soil drench and several had higher ratios after foliar sprays. Chemical name used: ß-[(4-chlorophenyl)methyl] (l,l-dimethylethyl)-l-H-1,2,4-triazole-l-ethanol (paclobutrazol, PB).

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M.L. Arpaia, G.S. Bender, and G.W. Witney

A project evaluating the performance of cv. Hass on eight clonal avocado rootstocks—G755A, G755B, G755C, Duke 7 (D7), Borchard (BR), D9, Toro Canyon, and Topa Topa was established in southern California in 1986. Two additional rootstocks, Thomas and G1033, were added in 1987. Of the trees planted in 1986, the BR and D7 rootstocks have consistently had the highest total yields for all rootstocks, whereas the three G755 selections have had the lowest productivity. No differences in productivity between the two rootstocks planted in 1987 have been detected. The influence of rootstock on the magnitude of alternate bearing will be discussed, although the oscillation in yield is greater for the higher-yielding rootstocks. Tree size has been measured throughout the study. The BR selection has consistently produced a larger tree, even though it has continued to have high productivity. There are no consistent differences between the other rootstocks. Yield efficiency, measured as the kg fruit/m3 of canopy volume has been calculated. In selections that are prone to severe alternate bearing, the swing in yield efficiency is also the greatest. The data thus far suggests that a yield efficiency of ≈2.5 kg fruit/m3 canopy volume is the maximum yield possible for California `Hass' avocado.

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Chenping Zhou, Ruiting Chen, Yaqiang Sun, He Wang, Yi Wang, Ting Wu, Xinzhong Zhang, Xuefeng Xu, and Zhenhai Han

, fruit-set, plant vigor, fruit characteristics, leaf photosynthesis, shoot hormone, and carbohydrate content in the bridge-grafted, girdled apple trees to better understand the effect of M9 bridge grafting on trunk-wounded apple trees and to provide

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Masahiko Fumuro

consumption of mango fruit. However, ‘Aikou’ has strong tree vigor, so it is likely to be higher than ‘Irwin’. Furthermore, this cultivar needs more exposure to light for coloring the peel than does ‘Irwin’. Another problem with pot cultivation is that the

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Lenny Wells

additional pecan hectares from 2010 to 2014. The majority of these new pecan plantings are equipped with microsprinkler or drip irrigation systems ( Wells, 2014 ). Cultural practices that promote tree growth and vigor during the establishment phase are