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Taproots of 2-year-old `Apache' seedling pecan [Carya illinoensis (Wang)] trees were pruned to 1 ft (30 cm), 2 ft (60 cm), or 3 ft (90 cm) in combination with wounding treatments consisting of no wounding, scraping through pericycle tissue on one or two sides of the taproot, or longitudinally splitting the taproot for about half its length. The trees were planted in a Port silt loam soil and a Teller sandy loam soil and grown without irrigation. At the end of the first and second growing seasons, top growth was measured, trees were dug and root system regrowth was evaluated. Tree root weight and number of roots per tree decreased with increasing taproot length.

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Patch budding is a common propagation technique for pecan (Carya illinoinensis) commonly used in the central and western United States, but seldom used in the southeastern United States. Success rates vary, but 75% is normally an acceptable survival rate. Selected budwood and rootstock treatments were evaluated to improve budding success. Additional studies were conducted to evaluate bud forcing techniques that would leave the rootstock intact, allowing a second bud to be inserted if the first patch bud failed. Girdling exceptionally vigorous shoots at the base used for budwood improved success, but neither tip pruning shoots used for budwood or rootstock affected patch bud survival. Patch budding was more successful using budwood from 1-year-old branches than from current season shoots, a finding that greatly extends the window available for propagation using patch buds. The age of rootstock wood at the budding site did not affect patch bud survival. Girdling the rootstock immediately above the dormant patch bud was less effective than top removal for forcing the patch bud in the spring. Application of a lanolin paste of 0% to 5% 2,3,5-triodobenzoic acid (TIBA) or 0.02% 6-benzylaminopurine (BAP) to a girdle immediately above the patch bud was positively related to the percentage of patch buds forcing when tree tops were left intact. The combination of girdling, 5% TIBA, and 0.02% BAP resulted in 76% of the buds forcing compared with 73% forced using top removal. This approach damages trees less and enables a second chance for patch budding on a stronger tree.

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Pecan (Carya illinoinensis) nuts with cracked shells reduce market grade and are usually removed during pecan cleaning. One type of crack is the shell suture that splits on certain cultivars with thin shells and high kernel percentages. ‘Schley’ nuts with diverse kernel moisture concentrations were dislodged from trees on cloudy and sunny days and exposed to ambient environmental conditions for 1 day on the ground. Samples were collected immediately after dislodging and after 1 day’s exposure, sealed in a plastic bag that was placed in a cooler, and then transported to the laboratory where they were assessed for kernel moisture and split sutures. The number of nuts with split sutures was unaffected by kernel moisture percentage or sunlight exposure when samples were collected immediately after dislodging. However, after 1 day, nuts with high kernel moisture percentages with high solar radiant exposure (sunny day) had substantially more nuts with suture splits than those with low solar radiant exposure (cloudy day). At the lowest kernel moisture percentages, the number of nuts with split sutures was insensitive to solar radiant exposure. During the first harvest, ‘Schley’ trees should be shaken to dislodge nuts on cloudy days and harvested before exposure to bright sunshine to minimize suture split. This probably extends to other cultivars with a history of suture split. An alternative to shaking on cloudy days, though not tested, might be to shake trees in the evening and harvest the next morning before exposure to high light conditions. Later, during the harvest season when kernel moisture was lower, sunlight exposure has little, if any, effect on suture splits.

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Abstract

Seedling pecan tree [Carya illinoensis (Wangenh) C. Koch] roots were flooded for 28 days while trees were either dormant, beginning budbreak, or in active growth, plus an unflooded control. Flooding roots while trees were dormant did not affect growth and seldom affected leaf elemental concentrations compared to unflooded trees. Trees with roots flooded during budbreak usually had less leaf area and were shorter, with smaller trunks than unflooded trees. Leaf N and Fe concentrations were decreased immediately after flooding, but, 56 days after trees were drained, P, Ca, Mg, Zn, and Mn concentrations were greater than in unflooded trees. Leaf area, tree height, trunk diameter, and leaf and trunk dry weights were not affected by flooding during active growth. Root dry weight was reduced 31% immediately after trees were drained, and 48% 56 days after trees were drained compared to unflooded trees. Trees flooded during active growth had lower concentrations of N, P, K, Ca, Mg, Zn, Fe, and Mn immediately after flooding, but, 56 days after trees were drained, leaf elemental concentrations were not significantly different from unflooded trees.

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Abstract

Nitrogen and K were applied to 26-year-old ‘Western’ pecan [Carya illinoensis (Wangenh.) C. Koch] trees at 0, 56, 112, or 224 kg ha−1, and 0, 93, or 186 kg ha−1, respectively, for 6 consecutive years (1978–1983). There was a positive relationship between N rate and leaf N concentration and shoot growth. The number of new shoots per 1-year-old shoot was increased by N application. Yield was greater using 56, 112, or 224 kg N ha−1 than no N. Nitrogen rate was negatively related to leaf K concentration and curvilinearly related to leaf Mn concentration, but did not affect leaf Ca or Mg. Leaf P and Zn concentrations were reduced during some years by N application. Potassium application increased leaf K concentration in 1980, 1982, and 1983, but did not affect leaf K concentration in other years. Surface applied K moved to the 30–45 cm depth by 1980 and to the 45–60 cm depth by 1982. Potassium rate was positively related to leaf Mn concentration, but not leaf N, P, Ca, Mg, or Fe concentration. Annual yield was increased by K rate only in 1979, but cumulative yield was positively related to K rate.

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Low yields and high harvesting costs are long-standing problems in mango (Mangifera indica L.) cultivation. In an effort to increase productivity in the scion 'Kensington Pride' we examined the impact of nine different rootstocks over a 10-year period. Rootstock effects on fruit production were significant in most seasons, and cumulative yields (nine seasons of cropping) for the best treatment ('Sg. Siput') exceeded those of the poorest treatment ('Sabre') by 141%. Yield efficiencies (expressed on both a trunk cross-sectional area and canopy silhouette area basis) were also significantly affected by rootstock. Rootstock effects on yield and yield efficiency were generally consistent across seasons, despite large seasonal variations in yield. Harvest rates were also influenced by rootstock, and were poorly correlated with tree size. These results demonstrate possibilities for manipulating mango scion productivity through rootstock genotype.

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Abstract

Flower buds of peach (Prunus persica Batsch) and apple (Malus domestica Borkh.) leached with water for 6 hours were less cold-hardy than nonleached buds. Buds which were leached with water for 16 hours and then dried for 0 to 16 hours were equally damaged by freezing; however, their moisture content decreased as drying time increased. Cold-hardiness was reduced rapidly during the first 3 hours of leaching, then loss of hardiness slowed and remained nearly constant through up to 48 hours of leaching. Loss of hardiness appears to be closely associated with leaching of water-soluble compounds from the flower bud, a loss which reduces the bud's ability to supercool.

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The productive life of a pecan [Carya illinoinensis (Wangenh.) K. Koch] orchard frequently spans two or more generations, but eventually orchards require renewal. Weather events damage tree canopies, pests affect tree health and productivity, and new cultivars offer greater yield potential or better nut quality. A popular method of orchard renewal is selective tree removal combined with interplanting new trees. Many old pecan orchards in the southeastern United States are infected with crown gall [Agrobacterium tumefaciens (Smith and Townsend) Conn.], potentially a problem for interplanted trees. Two tree types, nursery-grafted trees and seedling trees that were grafted 3 years after transplanting, were evaluated 6 years after transplanting. Transplanted trees varied in distances from established 80-year-old trees or residual stumps after tree removal. Ten trees near the study site, located 3.6 m from crown gall-infected stumps, were excavated to determine disease incidence. No crown gall was observed on any of the 87 trees in the study or the excavated trees. Trunk diameters of interplanted trees increased as distance from the nearest stump decreased and distance from the nearest established tree increased. Leaf elemental concentrations of the 6-year-old transplants were not related to observed growth differences. Conclusions include 1) stumps promoted rapid transplant growth; 2) crown gall infections of transplanted trees were unlikely even when crown gall symptoms were obvious on adjacent trees and stumps; and 3) transplant growth was suppressed by established trees.

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Pecan (Carya illinoinensis) leaf elemental concentrations are the industry standard to guide fertility programs. To provide meaningful information, a standard index tissue collected at a specific development stage is required along with established elemental sufficiency ranges. We report pecan leaf elemental sufficiency ranges used in Oklahoma that were developed based on research in Oklahoma and elsewhere. In addition, fertilizer recommendations, based on various leaf elemental concentrations, are included.

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Perennial legumes ground covers were evaluated in pecan (Carya illinoinensis) orchards to supply nitrogen and increase beneficial arthropods. Ground covers were `Kenland' red clover (Trifolium pratense), `Louisiana S-1' white clover (Trifolium repens), a mixture of these two legumes, or bermuda grass (Cynodon dactylon), each in 5 ha plots. Nitrogen was applied at 0-200 kg·ha-1 N in 50 kg intervals to bermuda grass plots, and was omitted on the legumes. Aphids feeding on the legumes attracted lady beetles; however, lady beetle populations in the tree canopies were not affected by ground cover treatment. The most abundant lady beetle species in legumes were Coleomegilla maculata lengi (77%) and Coccinella septempunctata (13%); whereas, dominant species in tree canopies were Coleomegilla maculata lengi (33%). Olla v-nigrum (20%). Cycloneda munda (18%) and Coccinella septempunctata (15%). Several other beneficial arthropods were sampled in legumes and tree canopies. Aphid populations feeding on pecans were low (peak population ≈ 2 aphids/leaf), and not affected by ground cover treatment. Legumes supplied the equivalent of applying 68-156 kg·ha-1 N.

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