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  • Author or Editor: Michael W. Smith x
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Fruit of `Mohawk' in 1986 and 1988 and `Shoshoni' pecan [Carya illinoensis (Wangenh.) C. Koch] in 1986 were thinned during early August using a pecan shaker with modified shaker pads. Fruit removed ranged from 44% to 57% of the crop load. Fruit thinning increased nut size of `Mohawk' in both years, but did not affect nut size of `Shoshoni'. Kernel percentage of thinned `Mohawk' and `Shoshoni' trees increased, and kernel grade of `Mohawk' improved relative to unthinned trees. Return bloom of `Mohawk' was not affected either year by thinning, but return bloom on `Shoshoni' was increased by thinning. Mechanical fruit thinning appears to be a useful commercial tool until better thinning methods are available.

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Irrigation schedules were evaluated on `Cresthaven' to determine if water could be conserved without reducing fruit size or yield. Tensiometers were used to schedule trickle irrigation in 1984-88. Treatments were no irrigation or irrigation when soil matric potential reached 40 or 60 KPa 30 cm deep. When production began in 1986, trees were either irrigated until Oct. or until after harvest (1-7 Aug.). In 1989, class A pan evaporation was used to schedule irrigation by replacing 100% evaporation. Trees were irrigated from bud break to harvest or Oct., beginning at stage III fruit growth to harvest or Oct., or not irrigated. The irrigation treatments were in factorial combination with an annual ryegrass ground cover or herbicidestrip. The ryegrass was seeded in Oct., then killed at the onset of stage III fruit growth. Water application was reduced 50% when irrigation was discontinued after harvest compared to irrigation until Oct. Non-irrigated trees had smaller trunks than irrigated trees; however, there were no differences in trunk size among irrigation treatments. Non-irrigated trees yielded less total fruit and fruit over 7-cm diameter than trees irrigated until Oct., but there were no significant differences in yield among irrigated trees. Flower bud density or fruit set was not affected by treatment. The orchard floor management did not affect tree growth or yield.

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Alternate bearing of pecan [Carya illinoinensis (Wangenh.) K. Koch] remains the leading problem of the industry. Several cultural practices have been developed or improved to mitigate alternate bearing. Premature defoliation was one problem identified that substantially decreased return bloom. The objective of this study was to determine the response of individual shoots exposed to various defoliation treatments. In one study, individual vegetative or bearing shoots were hand-defoliated in mid-September. Defoliation was the basal one-half, distal one-half, entire shoot, or not defoliated. Another study applied the same defoliation treatments to bearing shoots in July, August, or September. Defoliation had minimal effects on return bloom and rarely affected the percentage of current-season shoots fruiting the next year. Defoliation date also had little effect on return bloom. These data indicate that individual shoot response to defoliation was not autonomous and has implications for determining crop overload and needed mechanical fruit thinning.

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Phosphorus (P) and potassium (K) deficiencies were identified in a ‘Pawnee’ pecan [Carya illinoinensis (Wangenh.) C. Koch] orchard. Deficiencies of P and K have traditionally been difficult to correct in pecan. Broadcast application of P rarely results in a positive response. Broadcast applications of K frequently require 3 or more years before a positive response was noted, particularly in soils with high clay content. A 4-year study was initiated on 10-year-old trees using soil band-applied P, K, blended P plus K, and a non-treated control. Rates were based on trunk cross-sectional area adjusted annually for tree growth. Phosphorus application alleviated leaf deficiency symptoms, increased leaf P concentration, and improved flowering. However, P application resulted in darker kernels than the control or K-treated trees. Band-applied K was not associated with observed leaf symptoms but increased leaf K above the recommended minimum level and increased the percentage of number-1 kernels. Band-applied P or blended P plus K suppressed leaf K concentrations. Blended P plus K applied as a band appeared to improve return bloom 2 of 3 years, although no improvement in leaf K concentration was noted.

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Leachates of living Cynodon dactylon (L.) Pers. and Amaranthus sp. were applied to Carya illinoinensis (Wangenh.) C. Koch. seedlings to compare effects on growth and elemental absorption. Water applied to the weed pot or control pot (no weeds present) leached through the pot and into a funnel with a tube attached, then directly into the corresponding pecan seedling pot. After 4 months of growth, pecan seedlings receiving weed leachates had less leaf area and were shorter than those watered through control pots. These results suggest that leachates from these two weed species inhibit pecan growth, independent of any competition effects.

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Growth of `Apache' pecan [Carya illinoinensis (Wangenh.) K. Koch] seedlings was evaluated for 3 years when grown in a 11.2-m2 weed-free area or when various combinations of one or two plants of cutleaf evening primrose (Oenothera laciniata Hill), a cool-season species, or Palmer amaranth (Amaranthus palmeri S. Wats.), a warm-season species, were grown 30 cm from the tree, with the rest of the 11.2-m2 area weed-free. Either weed species alone suppressed tree growth compared to the weed-free control. A temporal succession of primrose followed by amaranth reduced growth most. After 3 years, two plants of primrose followed in succession by two of amaranth caused a 79% reduction in cumulative current-season's growth.

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Abstract

Roots of 53-day-old pecan seedlings [Carya illinoensis (Wangenh.) C. Koch] were either not flooded or flooded by submerging pots to ≈2 cm above the soil line in containers of water. Leaf gas exchange measurements at 1000 µmol·s–1·m–2 photosynthetic photon flux, 340 µl·liter–1 CO2, and 27°C were made prior to flooding, after 1, 8, or 15 days of flooding, and 7, 14, or 21 days after flooding was terminated. Net CO2 assimilation rate (A) decreased 56% after 1 day of flooding. Flooding 9 or 15 days did not further depress A. Carbon assimilation of trees that had been flooded for 8 days and then returned to nonflooded soil for 7 days were similar to unflooded trees. In contrast, A of seedlings flooded 15 days did not regain the A of unflooded trees 14 days after flooding terminated. Transpiration rates (E) paralleled A in all treatments. Leaf conductance to CO2 (g L ) was positively correlated with A (R2 = 0.94). However, leaf internal CO2 (Ci) concentration was not decreased by reduced gL. Water potential (ψ l ) and turgor potential (ψP) of leaves were higher when trees were flooded, but osmotic potential (ψs) was unaffected.

Open Access

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.

Open Access

Abstract

The linear propagation of ice in peach [Prunus persica (L.) Batsch] shoots was measured during and after bloom. The mean rate of ice propagation was 9.3 ± 2.3 mm·s-1 at — 3C, with no significant differences observed among ‘Redskin’, ‘Reliance’, and ‘Redhaven’ cultivars. No barriers to the spread of ice were observed. Flowers froze within 30 sec from the time the advancing ice front passed their location on the stem. No ice-nucleation active bacteria were detected on the shoots or flowers.

Open Access

Abstract

During the winter of 1983-84, 2 periods of below normal temperatures caused severe damage to ‘Western’ pecan trees [Carya illinoensis (Wangenh.) C. Koch]. Leaf elemental concentrations of N, P, K, Ca, Mg, Mn, Fe, and Zn, and yield/tree, measured during 1983, were evaluated to determine their relationship to damage. The only factors significantly related to the amount of cold damage were N, P, and yield/tree. Leaf N2 and leaf P2 were inversely related, whereas yield was positively related to cold damage.

Open Access