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The modified Mitscherlich plant growth model was used to quantify the threshold leaf Zn level influencing nut yield and vegetative growth, on an orchard basis, for pecan [Carya illinoinensis (Wangenh.) C. Koch]. Four indices of tree performance, including percentage of trees without deficiency symptoms, vegetative growth, nut yield, and trees without deficiency symptoms plus nut yield, were analyzed with regard to leaf Zn concentration. Data available from published and unpublished sources on any single performance index were combined for mathematical modeling. The threshold value for leaf Zn was determined to be ≈50 μg·g-1 for these tree performance indices. Thus, nut yield and vegetative growth in an orchard will be reduced with a leaf Zn concentration below ≈50 μg·g-1, but will not be affected above this value.

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The regenerative capacity of mature pecan [Carya illinoinensis (Wangenh.) K. Koch] embryonic tissues was demonstrated after pretreating mature nuts to eliminate associated endogenous contaminants. Cultured cotyledon segments were induced to form adventitious roots in a medium with 50 μm NAA. A regeneration medium with 20 μm BA and 5 μm IBA stimulated prolific axillary shoot production from the embryonic axis without causing cotyledon abscission. Cotyledon retention was essential for shoot initiation and long-term development. Eighty-five percent of the shoots emerging from embryonic axes formed at the cotyledonary nodes. Thirty percent of the microshoots rooted on an auxin-free medium after preculture in a medium with 20 μm IBA. TDZ (25 μm) stimulated callus production from the cotyledonary nodes and radicles. Adventitious buds emerged on the callus surface and internally in callus. Chemical names used: a -naphthaleneacetic acid (NAA); 6-benzylaminopurine (BA); indole-3-butyric acid (IBA); N-phenyl-N'-1,2,3-thidiazol-5-ylurea (TDZ).

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Organic mulches (leaves, pine nuggets, pine straw, grass clippings, and chipped limbs) were applied at depths of 10, 20, or 30 cm in a 3 × 3-m area around young pecan [Carya illinoinensis (Wangenh.) K. Koch] trees. These treatments were compared to an unmulched herbicide treatment and a common bermudagrass [Cynodon dactylon (L.) Pers.] sod. Trunk cross-sectional areas (TCSAs) of the mulched trees were larger than those of trees in the sod or unmulched plots and increased linearly as mulch depth increased. All mulches influenced TCSA similarly. Mean TCSA for mulched trees increased 14-fold compared to an increase of 8-fold for the unmulched trees and the sod in this 3-year study. Thus, common yard-waste mulches can be used effectively to increase growth of young pecan trees.

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Pecan [Carya illinoinensis (Wangenh.) C. Koch `Melrose'] and pear (Pyrus calleryana Decne. `Bradford') trees in the nursery grew more in containers designed to hold water in the lower portion. The water-holding reservoir was obtained either by placing 76-liter containers in a frame holding water to a depth of 6 cm or by using containers with drainage holes 6 cm from the bottom. Continuous waterlogging at the bottom of containers resulted in root pruning and root death in the lower portion of the containers, but roots grew well above the constantly wet zone. Fresh weight of plant tops and trunk diameters were greater after two growing seasons in the containers with water reservoirs compared to those grown in similar containers with no water reservoirs. Total root dry weight was unaffected.

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`Western Schley' pecans [Carya illinoinensis (Wangenh.) K. Koch] were evaluated for flavor by a 17-person sensory panel after oven-drying nuts that had been harvested 1 to 7 weeks before normal harvest in 1985. The nuts were 1) not dried, 2) oven-dried 24 hours at 29C, 3) oven-dried 24 hours at 35C, 4) oven-dried 30 hours at 29C, 5) oven-dried 30 hours at 35C, 6) dried at room temperature for 72 hours, and 7) collected at normal harvest time (control). At the start of the experiment, kernel moisture was ≈ 14%. Some of the treatments reduced kernel moisture to <5 % the first week of the experiment, but drying nuts at room temperature for 72 hours reduced kernel moisture as effectively as other treatments. Judging by kernel flavor, pecans can be harvested ≈ 4 weeks before normal harvest (performed after the first freeze in Las Cruces, N.M.) and artificially dried without affecting flavor.

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Annual legume ground covers were evaluated in pecan (Carya illinoinensis) orchards to supply nitrogen and increase beneficial arthropods. Treatments were established at two sites, each with 5 ha of a `Dixie' crimson clover (Trifolium incarnatum) /hairy, vetch (Vicia villosa) mixture and 5 ha of grass sod. Data indicated that the legume mixture supplied over 100 kg·ha-1 N to the pecan trees. Beneficial arthropods were greater in orchards with legume ground covers than in orchards with a grass groundcover. Lady beetles and green lacewings were the most important spring predators, and green lacewings were the most important fall predator. The Species distribution on the ground covers differed from that in the canopy. Coleomegilla maculata lengi, Hippodamia convergens and Coccinella septempunctata were the most abundant lady beetle species in the legume ground covers, and Olla v-nigrum, Cycloneda munda, and Hippodamia convergens were the most abundant species in the pecan canopies. Beneficial arthropods appeared to suppress injurious pecan aphids.

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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.

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Putative resistance to the yellow aphid complex (Monellia caryella (Fitch) and Monelliopsis pecanis Bissell) in the `Pawnee' pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivar was first noted in greenhouse tests by rating cultivars for relative amounts of honeydew on adaxial leaf surfaces. This resistance was confirmed in two field tests monitored from mid-June to mid-Oct. `Pawnee' supported significantly lower aphid populations during every rating period when relatively large numbers of these insects were present. `Navaho' also showed resistance, with `Desirable' having intermediate resistance and `Stuart' being very susceptible. Insect populations were also monitored on the four quadrants of each tree, with this quadrant effect being significant in only one test. This test had the highest populations on the West and lowest populations on the East.

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Scion wood of `Desirable' pecan [Carya illinoinensis (Wangenh.) K. Koch] was grafted onto the lateral roots of 70-year-old `Van Deman' seedling rootstocks for evaluation as an alternative to planting nursery-grown trees for orchard cultivar conversion. Grafting treatments included application of IBA, method of grafting, position of graft, and grafting time. Survival was higher for grafts treated with IBA than those without IBA, for modified bark grafts positioned beneath the soil line than for either modified hark grafts positioned above the soil line or inlay grafts, and for grafts made 6 to 8 weeks after budbreak than later in the season. Techniques developed in this study demonstrate that cultivar conversion of > 75% is possible. Chemical name used: lH -indole-3-butyric acid (IBA).

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Thirteen cultivars of pecan [Carya illinoinensis (Wangenh.) K. Koch] were monitored for bud break, pollen shed and stigma receptivity for 4 years at LSU Pecan Station, Robson, LA. Cultivars were generally consistent in displaying clear patterns of protogyny or protandry, although patterns were uncertain for some cultivars in some years. Mean dates of cultivar phenology varied significantly by year. Years with warm winter and spring temperatures had earlier seasons of growth and flowering than years with cooler temperatures. The duration of pollen shed and stigma receptivity varied between years. Protogynous cultivars, as a group, had greater bloom overlap than protandrous cultivars, although overlap varied between years for both dichogamy classes. The sequence of cultivar flowering relative to other cultivars varied between years, resulting in variable amounts of bloom overlap between cultivars in different years.

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