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Abstract

One-time tillage treatments in a 70-year-old ‘Moneymaker’ pecan [Carya illinoensis (Wang.) K. Koch] orchard with traffic-induced soil compaction, showed nut yields to be increased by disk harrowing in comparison to the untilled check or subsoiling treatments. All tillage treatments increased soil pH in the surface soil, with leaflet Zn and Al levels declining and B levels increasing in tilled vs. nontilled treatments. Tillage had no influence on leaflet N, P, K, Ca, Mg, Fe, or Cu levels. Periodic disk harrowing appears to be a beneficial cultural practice for increasing nut yield in orchards with certain soil compaction problems. Harrowing also improves soil pH by incorporating surface applied lime into the plow layer.

Open Access

Excessive Stage II fruit drop (i.e., June drop) often limits profitability of certain pecan [Carya illinoinensis (Wangenh.) C. Koch] cultivars. Anecdotal evidence indicates that one cause of drop is linked to a nutrient element deficiency. This study examines the consequences of improving tree potassium (K) nutrition on fruit drop, nutmeat yield, and kernel quality (i.e., % kernel) in ‘Desirable’ orchards in which generally accepted foliar analysis standards indicate satisfactory tree K nutritional status (i.e., 0.75% or greater to 2.5% K/dry weight). Multiyear field studies of two such orchards found that elevating leaf and fruit K concentration through soil banding of potash over drip irrigation emitters: 1) increased fruit retention by reducing Stage II fruit drop; 2) increased in-shell nut yield; and 3) increased nut quality by increasing percentage kernel. Potash applied through soil banding elevated foliar and fruit K concentration by ≈ 0.1% to 0.4% units within a few months post-application depending on the amount applied; however, the beneficial effects of a single potash soil band application diminished after the first year. A comparison of the K concentration of retained fruit versus abscised fruit during the Stage II fruit drop window found that retained fruit possessed endogenous K concentrations of 1.2% to 1.7% (dry weight basis) in one orchard and 1.45% to 1.9% in a second orchard, whereas aborted fruit possessed K at 0.65% to 1.2% in one orchard and 0.75% to 1.2% in a second orchard, respectively, thus establishing ≈ 1.25% K as a “drop threshold” under conditions of this study. The total K concentration of retained fruit is typically 0.25% to 0.50 K/dry weight greater than dropped fruit. Considerable K-associated late-spring fruit drop can occur in ‘Desirable’, although early- to midsummer leaf analysis indicates trees were K-sufficient, hence implying that young fruit likely possesses a higher K requirement than does foliage. These K-associated benefits to trees meeting accepted K sufficiency criteria is evidence that K nutrition management of ‘Desirable’ pecan merits r-evaluation and possibly pecan K nutrition in general.

Free access

The existence of nickel (Ni) deficiency in certain horticultural crops merits development of fertilizer products suitable for specific niche uses and for correcting or preventing deficiency problems before marketability and yields are affected. The efficacy of satisfying plant nutritional needs for Ni using biomass of Ni hyperaccumulator species was assessed. Aqueous extraction of Alyssum murale (Waldst. & Kit.) biomass yielded a Ni-enriched extract that, upon spray application, corrects and prevents Ni deficiency in pecan [Carya illinoinensis (Wangenh.) K. Koch]. The Ni-Alyssum biomass extract was as effective at correcting or preventing Ni deficiency as was a commercial Ni-sulfate salt. Foliar treatment of pecan with either source at ≥10 mg·L–1 Ni, regardless of source, prevented deficiency symptoms whereas treatment at less than 10 mg·L–1 Ni was only partially effective. Autumn application of Ni to foliage at 100 mg·L–1 Ni during leaf senescence resulted in enough remobilized Ni to prevent expression of morphologically based Ni deficiency symptoms the following spring. The study demonstrates that micronutrient deficiencies are potentially correctable using extracts of metal-accumulating plants.

Free access

A decision support system (DSS) is described that quantitatively analyzes certain important light climate characteristics of crops planted in discrete canopy, hedgerow, or trellis cropping systems. The DSS facilitates rapid and efficient calculation of the theoretical maximum shading (or, conversely, the theoretical minimum level of insolation) for use in determining the planting pattern that minimizes canopy shading during user-specified temporal intervals. It addresses canopy shading in field plantings within a wide variety of geometric patterns, interplant spacings, canopy sizes and forms, global latitudes, pattern orientations, site reliefs and aspects. Calculations describe insolation characteristics during any hour(s) of the day or day(s) of the year within the range of planting parameters. The DSS functions as a systems tool, or module, for design of the spatial subsystem component of a particular cropping strategy where horticulturally important traits are regulated by the light climate.

Free access

The authors have developed a mathematical model designed for shade-intolerant tree crops which describes the amount of intertree shading in an orchard. These data are used to formulate an optimal orchard design based on shading reduction in orchards for any tree crop during any developmental window at any global location for either continuous canopy hedgerows or non-intersecting canopies for several different orchard geometries. Variables include tree shape, orchard geometry intertree spacing, row orientation, time and day of year, and geographical coordinates. Optimal orchard designs are based upon the total amount of unshaded canopy surface per unit area which each orchard configuration confers. Results indicate extensive variability of intertree shading between hedgerow and non-intersecting canopies to be largely a function of latitude, regardless of other variables.

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Effective nitrogen (N) management promotes consistent and abundant pecan [Carya illinoinensis (Wangenh.) C. Koch] production while minimizing waste. Recovery and partitioning characteristics of N potentially affects N management decisions; for this reason, we report certain N characteristics exhibited by trees in a bearing ‘Pawnee’ orchard. Nitrogen was applied prebudbreak (PBB) as a single 10 Mar. application at 1.689 g·cm−2 cross-sectional trunk area or a split application in Mar. (70%) followed by a midsummer application during rapid fruit development (RFD) on 28 July (30%) (i.e., PBB + RFD) using 15N-enriched fertilizer. Recovery of N by trees the first year was 7.2% from the PBB application and 11% from the RFD portion of the split application. Nitrogen application was 210% larger at PBB (Mar.) than at RFD (July), resulting in 118% more N absorbed. At harvest in November, fruit contained 41% and 36% of total N recovered during the first year from the PBB and RFD treatments, respectively. About 3% of the total fruit N was derived from fertilizer (NDF) absorption during the current year. Recovery was 12% for the PBB treatment and 19% for the RFD treatment by the end of the second growing season, with 93% more N absorbed from the PBB application. Nitrogen recovered from the PBB application increased ≈50% while trees were dormant, but there was little change in N recovery when applied during RFD. During the year of application, NDF was similar in shuck, shell, and kernel tissue when 15N-enriched fertilizer was applied PBB. When applied at RFD, more NDF was in the kernel than the shuck and shell, indicating rapid absorption and transport to the fruit, especially to the developing kernel. In both treatments, most fruit N was derived from tree storage reserves. In the second year, NDF was highest in shucks and lowest in kernels for the PBB application; thus, N enrichment from the previous year was being depleted. In contrast, NDF was higher in kernels than shucks and shells when 15N-enriched fertilizer was applied during RFD the previous year, indicating that N applied during RFD the previous July was being absorbed in the latter part of the subsequent growing season. This study demonstrates that pecan trees maintained with adequate N nutrition derived the majority of N used for annual parts from stored N pools, although applied N was also rapidly absorbed and transported to N sinks. Dependence on endogenous N pools explains why pecans usually require at least 2 years to respond when N is withheld from well-managed trees. These results emphasize the importance of maintaining an annual N fertility program for current and future production.

Free access

Two years of observations on water availability, black aphids and leaf scorch provides evidence of substantial interaction among these factors. Foliage of irrigated trees of `Desirable', `Cheyenne', and `Wichita' cvs. exhibited much less leaf scorch, black aphid damage, free nitrogenous substances, and sugars than did nonirrigated trees.

Water stress appears to predispose foliage in such a way so as to greatly increase the ability of black aphids, and certain fungal pathogens to grow and/or reproduce on/in the affected foliage.

This appears to be associated with the organisms ability to induce biochemical changes that increase levels of free nitrogenous substances and sugars. The level and degree of chlorosis and area of foliar damage by black pecan aphids was much greater on nonirrigated trees.

Two years of observations on the relative resistance of about 50 cultivars resulted in genotype related differences in susceptibility to leaf scorch.

Free access

Aphids cause major annual economic losses to the U.S. pecan [Carya illinoinensis (Wangenh.) K. Koch] industry and are becoming harder to control with standard pesticides. An evaluation of efforts by certain growers to suppress aphid populations using air-blast sprays of 0.05% Silwet L-77, a non-ionic super-wetting organosilicone surfactant, indicated that: 1) reductions in blackmargined aphid [Monellia caryella (Fitch)] levels were mostly attributable to the air-blast spray effect rather than to the Silwet L-77 component; 2) a 0.05% solution of Silwet L-77 reduced net photosynthesis (A) of foliage by 5% for at least 14 days post-treatment; and 3) the efficacy of 0.05% Silwet L-77 sprays is not substantially increased by doubling the volume of spray per tree (1868 L·ha-1). However, higher Silwet L-77 concentrations were highly effective in killing aphids, although there was little or no residual activity. A response curve indicated that air-blast sprays of orchard trees with 0.30% (v/v) Silwet L-77 (at 934 L·ha-1) are capable of reducing yellow pecan aphid (Monelliopsis pecanis Bissell) populations by at least 84% while only reducing A by ≤10%. Chemical names used: silicone-polyether copolymer (Silwet L-77).

Free access

An assessment of vegetative traits of pecan [Carya illinoinensis (Wangenh.) K. Koch] from a range-wide provenance collection indicated the existence of at least two distinct populations within the native range (i.e., provenances north of Texas vs. provenances in Texas and Mexico). Southern most provenances generally broke bud earlier, retained foliage later in the fall, grew larger in height and trunk diameter, had narrower leaflet droop angles, had greater leaflet tilt angles, wider limb angles, greater Zn deficiency, less black pecan aphid susceptibility, and less red coloration to foliage than did northern most provenances. Trees originating from Jaumaua, in northern Mexico, were especially noteworthy insomuch that they were by far the tallest, possessed the largest trunk diameters, the longest foliation period, and lowest Zn deficiency ratings of all provenances. One family within this Jaumaua population also exhibited a high level of cold hardiness. Family heritability (hf 2) estimates were ≥0.48 for trunk cross sectional area, date of budbreak, leaf redness, cold injury, leaflet droop angle, and leaflet tilt angle, and ≤0.39 for late season leaf fall, black pecan aphid susceptibility, zinc deficiency, and branch angle.

Free access