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Bruce W. Wood

Canopy morphology of 83 pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivars differed in structural, size, and form characteristics. Cluster analysis identified two to five distinct classes for canopy height and diameter and their ratio, inclination angles for both major limbs and young shoots with lower-order structures, branch types, and canopy form and volume. Cultivar-related variability in these traits may have the potential for the improvement of pecan cultivars for factors such as light interception, cooling, air movement, and fruiting; thus, there is potential for identifying the development of canopy characteristics adapted to specific site conditions or cultural/management strategies.

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Bruce W. Wood

Pecan is wind pollinated, exhibits heterodichogamy and are either protandrous (I) or protogynous (II). Orchards are typically established using two complimentary flowering types but with no further scrutiny as to the degree of compatibility of these two types. Additionally, orchards are sometime established with a very low frequency of pollinator. An evaluation of several orchards revealed that yield losses are due to poor pollination is likely common. Data indicate that trees beyond about 46 m (150 feet) from a complementary pollinator exhibit substantial reductions in fruit-set; therefore, large block-type plantings are disadvantaged. Flowering data over several years show that Type I and Type II cultivars are often functionally noncomplementary, suggesting that pecan cultivars should also be identified with a seasonal identification (i.e., early, mid, and late). Data also indicate that dichogamy patterns substantially change as trees age or with abnormally warm or cool springs; hence, pollination patterns will vary depending upon orchard age. Data indicate that orchards should be comprised of 3+ cultivars. RAPD-DNA analysis of “hooked-nuts” indicates that this trait is not reliable as an indicator of selfing.

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Bruce W. Wood

Of 18 commonly used adjuvants evaluated on pecan [Carya illinoinensis (Wangenh) K. Koch], a few exhibited potential for substantially suppressing net photosynthesis (A) and the conductance of foliage to water vapor (g sw) when used within their recommended concentration range; however, most provided no evidence of adversely influencing A or g sw. Suppression of gas exchange by certain adjuvants persisted at least 14 days after a single application. The recently developed organosilicone-based surfactants generally exhibited the greatest potential for suppression. These data indicate that orchard managers should consider the potential adverse influence of certain adjuvants when developing orchard management strategies.

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Bruce W. Wood

Pecan [Carya illinoinensis (Wangenh.) K. Koch] nursery transplants performed best on establishment in nonirrigated orchards when using large trees planted early in the dormant season. After 6 years, growth and survival of bare-root transplants were equal to that of containerized transplants when established during the dormant season. Reducing transplant trunk height by ≤75% at planting did not affect subsequent tree survival, although rate of height growth and tree vigor increased such that there was no difference between pruned and nonpruned trees after 3 years, except that pruned trees appeared to possess greater vigor. There also were no differences in growth or survival between augured and subsoil + augured planting sites within 6 years of transplanting, and there were no differences between root pruned (severe tap or lateral root pruning) and nonpruned trees.

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Bruce W. Wood

The cyclic, alternate bearing and correlative aspects of U.S. produced pecan [Carya illinoinensis (Wangenh.) K. Koch] nuts are characterized. An attempt to forecast production using stepwise autoregressive techniques identified a national level biennial cycle for cultivar (CV) and seedling (SC) class nuts and a novemennial (9 year) cycle for SG class nuts. The intensity of the biennial cycle at the national level has generally been low to moderate over the last 50 years for CV and SG class nuts with no clear time trend being expressed. During the most recent years (1979-1991), national production of CV class nuts has not exhibited pronounced bienniality, whereas that of SG class nuts exhibited a moderate bienniality. The nature of the the irregularity of cycling of U.S. and state production appears to nullify the use of univariate polynomial equations as a practical tool for accurately forecasting nut production. Nut production within individual states was also cyclic, with 2-, 3-, 5, 6-, 10-, 12-, 14-, 15-, and 16-year cycles, depending on state and nut class. The most intense contemporary biennial cycles for CV class nuts were from Oklahoma, South Carolina, and North Carolina, whereas cycling of SG class nuts was most intense in Texas and Oklahoma. Correlations of production within and among states indicated that most interrelationships are relatively weak; however, national production of CV class nuts are highly correlated (r = 0.96) with the production of CV class nuts in Georgia, whereas that of SG class nuts is most correlated with that of Louisiana.

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Bruce W. Wood

Dormant season sprays of hydrogen cyanamide applied to pecan [Carya illinoinensis (Wangenh.) K. Koch] trees advanced budbreak, flowering, and shuck dehiscence. Hydrogen cyanamide was applied to dormant branches at ≈60, 45, 30, and 15 days before normal vegetative budbreak at rates of 0, 120, 240, 480, and 960 mm (corresponding to ≈0%, 0.5%, 1%, 2%, and 4%, solutions for 3 years). Depending on treatment, hydrogen cyanamide advanced budbreak by as much as 17 days, female and male flower maturity by up to 15 days, and nut ripening by as much as 14 days without reducing nut yield or causing phytotoxicity. Hydrogen cyanamide applied at 480 to 960 mm ≈60 days before expected budbreak possibly may be used commercially to advance ripening, manipulate time of pollen dispersal, and substitute for chilling when pecan is grown in mild environments.

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Bruce W. Wood

Long-term productivity of commercial pecan [Carya illinoinensis (Wangenh.) K. Koch] enterprises in relatively low-light environments such as the southeastern United States are limited by excessive tree crowding as orchards age. An effective horticultural strategy for countering this problem in relatively high-light environments is mechanical hedge-type pruning; however, uncertainty persists regarding the best strategies in low-light environments. This report describes the results of a 4-year study regarding the response of ≈25-year-old ‘Desirable’ pecan trees to different mechanical hedgerow-type, moderate canopy width (i.e., 2.43-m cuts from tree axis) pruning strategies. Canopy treatments were nonpruned control (NPC), annual dormant season side-hedge pruning on two faces, annual summer season side-hedge pruning on two faces, and alternating annual dormant season side-hedge pruning on a single alternating face. Relative to the NPC treatment, all three pruning strategies: 1) reduced in-shell nut yields by roughly 19% to 38%; 2) reduced marketable nut-meat yield by ≈19% to 36%; 3) failed to stimulate shoot development or fruiting within the central interior zone of tree canopies; 4) increased kernel percentage of nuts; 5) increased nut-meat grade; 6) substantially reduced alternate bearing intensity (I = 0.51 to ≈0.20); and 7) reduced orchard crowding. Pruning-associated reductions in nut yield appear sufficient to limit the commercial usefulness of annual or biennial mechanical hedgerow-type pruning of ‘Desirable’ pecan orchards at moderate canopy widths in relatively low-light environments such as the southeastern United States.

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Bruce W. Wood and Deane Stahmann

An ever increasing cost:price squeeze on the profitability of pecan (Carya illinoinensis) farming is driving a search for alternate husbandry approaches. `Wichita' and `Western' trees maintained at relatively high tree population density, by mechanized hedge pruning and topping, produced greater nut yield than an orchard treatment in which tree population density was reduced by tree thinning (144% for `Wichita' and 113% for `Western Schley'). Evaluation of three different hedge pruning strategies, over a 20-year period, identified a discrete canopy hedge pruning and topping strategy using a 2-year cycle, as being superior to that of a discrete canopy hedge pruning and topping strategy using an 8-year cycle, but not as good as a continuous canopy hedge pruning and topping strategy using a 1-year cycle. An evaluation of 21 commercial cultivars indicated that nut yields of essentially all cultivars can be relatively high if properly hedge pruned [annual in-shell nut yields of 2200 to 3626 lb/acre (2465.8 to 4064.1 kg·ha-1), depending on cultivar]. Comparative alternate bearing intensity and nut quality characteristics are reported for 21 cultivars. These evaluations indicate that pecan orchards can be highly productive, with substantially reduced alternate bearing, when managed via a hedge-row-like pruning strategy giving narrow canopies [3403 lb/acre (3814.2 kg·ha-1) for `Wichita' and 3472 lb/acre (3891.5 kg·ha-1) for `Western Schley']. North-south-oriented (N-S) hedgerows produced higher yields that did east-west (E-W) hedgerows (yield for N-S `Wichita' was 158% that of E-W trees and N-S `Western Schley' was 174% that of E-W trees).

These data indicate that mechanized hedge pruning and topping offers an attractive alternative to the conventional husbandry paradigm.

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Michael W. Smith and Bruce W. Wood

Allometric equations were developed for orchard-grown pecan [Carya illinoinensis (Wangenh.) C. Koch] trees. Trees, ranging in size from 22 to 33 cm in trunk diameter 1.4 m above the ground, were destructively harvested from two sites. The entire aboveground portion of each tree was harvested and then divided into leaves, current season's shoots, and branches ≥1 year old plus trunk. Roots were sampled by digging a trench beginning beneath the trunk and extending to one-half the distance to an adjacent tree, then separating the roots from the soil. Roots were then divided into those less than 1 cm in diameter and those ≥1 cm in diameter. Equations in the form Y = eaXb were developed to estimate dry biomass of most tree components and the whole tree, where Y is the dry weight, e is the base of the natural logarithm, X is the trunk diameter at 1.4 m above the ground, and a and b are coefficients. A linear equation provided the best fit for estimating the weight of the current season's growth. Power equations were also developed to estimate the weights of inner bark and wood for different size trunks or branches.

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M. Lenny Wells and Bruce W. Wood

Water-stage fruit-split (WSFS) is a relatively common and often major problem of certain pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivars. This study evaluates the possibility that the malady can be influenced by improving tree micronutrient nutrition. Foliar sprays of boron (B) and nickel (Ni) to WSFS-susceptible fruit of ‘Cape Fear’ and ‘Sumner’ are evaluated based on the possibility that either B or Ni potentially affects the severity of WSFS exhibited by trees. Although the incidence of WSFS on ‘Cape Fear’ was unaffected by micronutrient sprays, the severity of WSFS was substantially reduced in each of the 3 study years by foliar B application and in 2005 by foliar Ni application. Repeated foliar sprays of Ni also reduced WSFS of ‘Sumner’ fruit. These data indicate that improving either B or Ni nutrition can potentially reduce crop loss resulting from WSFS in certain orchard situations and provides evidence that insufficient availability of B or Ni to developing ovary tissues potentially predisposes developing fruit to WSFS when environmental triggers occur.