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newly established pecan trees increases trunk diameter, 2) pruning of newly established single-trunk tree scions will lead to fewer, but longer shoots, and 3) pruning will lead to higher total shoot growth. The findings generally support the second

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Five tree species, Platanus occidentalis L., Fraxinus americana L., Quercus palustris Muench., Liriodendron tulipifera L., and Gleditsia triacanthos L. f. inermis (L.) Zabel were wounded for 4 consecutive years. Four whorls of circular wounds or one whorl of elliptical wounds were cut into the trunk at widths of 10, 13, 17, and 25 mm. Tree growth was not measurably reduced by trunk wounding. Wound closure per unit of radial growth differed by species and annual growth.

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gibberellin acid (GA) content in the shoots ( Dann et al., 1985 ; Skogerbo, 1992 ). This hormone imbalance caused by trunk girdling might be associated with the altered carbohydrate metabolism, root growth, and vegetative growth ( An et al., 2017 ). Bridge

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In spring 1999, a commercial NAA (1-naphthaleneacetic acid) preparation for trunk sprout inhibition was compared with a corrugated plastic trunk wrap, aluminum foil wrap, bimonthly hand removal of sprouts, use of NAA preparation plus bimonthly hand removal when sprouts appeared, and a nontreated control. Three recently planted groves on three different rootstocks [`Midsweet' orange (Citrus sinensis)] on Swingle citrumelo (Citrus paradisi × Poncirus trifoliata), `Valencia' orange on Volkamer lemon (Volk, Citrus limon), and `Minneola' tangelo (Citrus paradisi × C. reticulata) on Smooth Flat Seville (SFS, Citrus hybrid) received each of the treatments in a randomized complete block experimental design with trees blocked by initial height and circumference. Every 2 months, sprouts were counted on each tree and removed from the hand removal treatments. After 1 year, all sprouts were removed and counted and height and circumference of trees was determined. Across all experiments, 82% to 100% of nontreated trees produced trunk sprouts and all sprout control methods significantly reduced sprouts per tree. NAA treatments were never significantly less effective at sprout suppression than the wraps at the P = 0.05 level, although in two experiments, wraps were more effective than NAA at P = 0.10. Time of sprout appearance varied between the three experimental blocks. Plastic and foil trunk wraps enhanced development of trunk circumference compared with nontreated controls in `Midsweet'/Swingle and `Valencia'/Volk. Greater trunk circumference resulted from use of wraps versus NAA in all three experiments, which appeared unrelated to differential sprout suppression. In these experiments, it appears that either wraps enhanced tree development beyond the suppression of sprouts or NAA influence on tree metabolism somewhat reduced trunk growth. The economics of the sprout suppression methods are also discussed.

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53 ORAL SESSION 17 (Abstr. 137–144) Growth & Development/Fruit & Nuts (Temperate)

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Radial trunk growth measured by the Verner dendrometer was reduced markedly due to competition for assimilates and water by greatly stimulated fruit growth resulting from the application of 2,4-D. These responses were accompanied by reduced water tension within the 2,4-D-treated trees, as indicated by less diurnal trunk shrinkage than that which occurred in control trees.

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Radial trunk growth of mature almond trees under 4 irrigation treatments was measured with Verner dendrometers for 4 consecutive years. Trunk growth rates and total seasonal growth were affected primarily by soil water and secondarily by crop density conditions. In early spring, when soil water was abundant (near field capacity in entire root zone), the rate of trunk growth was inversely correlated with crop density. Later on, trunk growth was influenced more by soil moisture conditions. Irrigation early in the season increased trunk growth rates even though 30 to 40% available water remained throughout the root zone at time of irrigation. Irrigations after mid-season merely maintained the prevailing trunk growth rates.

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Maleic hydrazide (MH) was readily translocated in the apricot tree, as indicated by inhibition of shoot growth and seed abortion in the fruits. However, cambial activity was undisturbed, and trunk growth proceeded normally.

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Trunk looping of several apple cultivars on seedling roots reduced terminal shoot growth and trunk enlargement below the loop and increased root suckers. Growth was reduced most in the early years of tree growth. In the 5th, 6th, and 7th growing seasons, annual trunk enlargement was not affected, but growth suppression in the 2nd, 3rd, and 4th years reduced final trunk diameter measurements after seven seasons. Similarly, terminal shoot length was suppressed greatest in the early years and to a lesser extent in the 5th through the 7th growing seasons. Fruit number was unaffected by looping in the 5th growing season, but looping increased fruit number and fruit/cm2 trunk cross-sectional area in the 6th and 7th seasons in ‘Golden Delicious’, ‘Starkrimson Delicious’, and ‘Northwest Greening’, but not ‘Stayman’.

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Mechanical harvesting using trunk shakers on late-season `Valencia' sweet orange [Citrus sinensis (L.) Osb.] trees can remove young fruit for the next crop and occasionally cause root exposure or severe bark scuffing on the trunk. To evaluate the effects of these physical injuries on fine root growth and lifespan, we installed minirhizotrons in the root zone of 15-year-old fruiting `Valencia' trees on Swingle citrumelo [C. paradise Macf. × Poncirus trifoliate (L.) Raf.] rootstocks. Images of roots against the minirhizotron tubes were captured biweekly with a custom-made video-DVD recorder system. Trees were harvested in early June by hand or with a linear-type trunk shaker in two consecutive years. Bark injury after trunk shaking was mimicked by removing part (42%) of the bark tissue from the main trunk with a sharp knife. Numbers of fine roots, root activity and lifespan as indexed by the color of the root, and the distribution of new fine roots after harvest were analyzed. Although root exposure was common with the normal operations during mechanical harvesting, few disturbances reached the major fine root zone. There was no clear correlation between root growth and trunk shaking with or without bark injury. The root system might benefit from less competition after the loss of young fruit from mechanical harvesting, as a greater availability of carbohydrates or other resources may compensate for any potential damage due to mechanical harvesting.

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