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- Author or Editor: Jerry A. Payne x
The reliability of a proposed satisfactory range of 50-100 ppm Zn in the leaflet for pecan [Carya illinoensis (Wang.) K. Koch] was tested. The range was compared to: a) the average Zn concentration in the leaflets of groups of trees where a variable percentage of trees had Zn deficiency symptoms and b) to the average Zn concentration in the leaflets of trees grouped according to severity of Zn deficiency. In both situations, Zn deficiency symptoms occurred only when Zn concentration in the leaflets was less than 40 ppm.
During a 6-year study, Zn levels in pecan [Carya illinoensis (Wang.) K. Koch] leaflets from equivalent Zn rates per 50-year-old tree were greater from broadcast than from band application. Equivalent amounts of Zn per tree were applied to the soil surface on a broadcast and band basis. Broadcast rates were 0, 20, 40, 80, or 160 kg of Zn/ha. Band rates were 0, 0.4, 0.8, 1.6, or 3.2 kg of Zn/tree applied in a 15-cm-wide band. Response from broadcast was quicker than from band application in that leaflet Zn was increased above the sufficiency level with 40 kg or more Zn/ha but only by the 3.2 kg of Zn/tree in the case of the band.
Ground applications of ZnO to large mature pecan [Carya illinoinensis (Wangenh.) K. Koch] trees in orchards possessing an acidic soil, but with a culturally induced slightly alkaline soil surface zone, were at least as effective as was ZnSO4 for rapidly correcting severe foliar Zn deficiency, improving in-shell nut production, and maintaining kernel quality. Under such soil conditions, light disking of Zn applied at 160 kg·ha-1 from ZnO elevated foliar Zn above the sufficiency level by the second growing season after application; whereas an absence of disking delayed substantial uptake from ZnO until the fourth growing season. ZnO, usually a lower priced Zn source, was as effective as was ZnSO4 for correcting Zn deficiencies via broadcast ground application; however, same season correction of Zn deficiency was best accomplished by the standard practice of using foliar sprays of ZnSO4 rather than by heavy soil applications of either Zn source.
Boron was soil applied to pecan trees (Carya illinoensis (Wang) K. Koch) at the rate of 0, 12.5, 25.0, 50.0, or 100 g per tree. Boron toxicity increased with B applied. Bud break the following spring was advanced in relation to B applied and toxicity incurred.
Ethylene was produced by the Chinese chestnut fruit (Castanea moltissima Blume), its rate increasing substantially prior to dehiscence. The primary site of synthesis was the involucre, rather than the seeds. Elevated levels (2 to 4 μl/kg-hr) of ethylene production by the involucre corresponded with increased respiratory activity; however, the rate of ethylene synthesis declined earlier in the senescence of the involucre than did the CO2 production. Exogenous application of ethylene either as a gas or as (2-chloroethyl)phosphonic acid (ethephon) accelerated the rate at which dehiscence occurred and improved the uniformity of dehiscence among seedling fruits.
A 4-year field study on pecan [Carya illinoinensis (Wangenh.) K. Koch] provided indirect support of the supposition held by some U.S. pecan growers that air-blast foliar sprays of potassium nitrate (KNO3) plus surfactant enhances nut yield. While these treatments did not measurably influence yield components, foliar K nutrition, or net photosynthesis, they did suppress “yellow-type” aphid populations. While air-blast sprays of water alone suppressed aphid populations, the inclusion of KNO3 plus surfactant provided an additional level of suppression.
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.