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  • Author or Editor: M. Lenny Wells x
  • HortTechnology x
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This study was established to assess the effects of a severe late spring freeze on flowering, shoot growth, leaf nutrient status, and the retention of fruit developing from secondary buds of pecan [Carya illinoinensis (Wangenh.) K.Koch]. Freeze damage appears to have a significant influence on pecan physiology and fruit retention. ‘Desirable’ produced a crop of pistillate flowers from secondary buds after the freeze; however, many of these flowers were abnormal in appearance. Freeze-damaged ‘Desirable’ trees exhibited shorter shoots, reduced flower and fruit retention, a lower chlorophyll index, and decreased leaf nitrogen concentration compared with nondamaged trees. Leaf zinc concentration was higher in freeze-injured ‘Desirable’ trees than in nondamaged trees. Freeze-damaged ‘Kiowa’ trees had longer shoots and failed to produce a crop of pistillate flowers from secondary buds on most shoots. Freeze damage led to the appearance of mouse-ear leaf symptoms and reduced leaf chlorophyll index, leaf nitrogen, and leaf magnesium concentrations in ‘Kiowa’. Leaf phosphorous and leaf potassium concentrations were higher in freeze-injured ‘Kiowa’ trees than in nondamaged trees. These observations provide insight into the potential response of bearing orchard trees injured by a late spring freeze.

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This study was established to assess the effect of aldicarb on newly transplanted pecan (Carya illinoinensis) nursery trees. Although labeled for use on pecans for more than 25 years, the aldicarb label for pecans was voluntarily dropped by the manufacturer in 2010. Bare-root seedling, ‘Cape Fear’, ‘Sumner’, and ‘Elliott’ trees were planted in Feb. 2007. Ten trees each were treated with one of the following treatments: aldicarb (0.25 lb at budbreak), aldicarb (0.25 lb applied at budbreak and again in June for a total of 0.5 lb/tree), and a nontreated control. Aldicarb increased shoot length, trunk diameter, leaf chlorophyll index, total dry weight, stem dry weight, and root dry weight of pecan seedlings after 1 year's growth. Aldicarb increased trunk diameter of ‘Cape Fear’, ‘Sumner’, and ‘Elliott’ during the course of the study. Nut production of ‘Cape Fear’ was enhanced in the third year of production. These observations indicate that aldicarb is of value in pecan orchard establishment.

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This survey addresses the current nutritional status of orchards typical of a large portion of the United States pecan (Carya illinoinensis) industry. A leaf nutrition and soil fertility survey was conducted for commercial orchards in a major production area of the U.S. pecan belt, which is located in southern Georgia. The study sampled pecan orchards from 18 July to 5 Aug. 2005 and 17 July to 3 Aug. 2008. All orchards had a history of commercial level orchard management, and represented a wide range of orchards typical of the region. Results indicate that southeastern U.S. pecan producers should focus their nutrient inputs on nitrogen (N), potassium (K), sulfur (S), and copper (Cu) as needed. The survey results show that leaf N can vary widely by season and among orchard locations. Evidence indicates that many growers could likely forego the soil application of phosphorous (P) and zinc (Zn) until leaf or soil analysis indicates a need. Orchard soil organic matter (SOM) in 2008 averaged 3.63%, and ranged from 1.74% on coarse-textured sandy soils to 5% on sandy loam soils. Both SOM and soil nitrate-N were higher in orchards using clover (Trifolium spp.) as a cool-season orchard groundcover than those using a grass sod only. The mean carbon:S ratio of Georgia pecan orchard soils was 504:1, which may further reduce tree uptake of S from low-S soils.

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A persistent problem was identified in pecan (Carya illinoinensis) orchards throughout southern Georgia in which pecan trees growing in rows immediately adjacent to peanut (Arachis hypogaea) fields developed hollow pecans. In-shell nut size and appearance was normal; however, the kernels failed to develop. In 2008 and 2009, research was conducted to evaluate the influence of imazapic on pecan nut development in two pecan orchards located at the University of Georgia Ponder Research Farm located near Tifton, GA. Three herbicide treatments were evaluated, including imazapic at 0.17 kg·ha−1, imazapic at 0.30 kg·ha−1, and a nontreated control. Imazapic inhibited pecan kernel production and shuck split during both years of study. In 2009, leaf potassium was reduced by the low rate of imazapic.

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A large number of agronomic and horticultural crops are susceptible to injury and yield loss from drift-level exposures to synthetic auxin herbicides. A new generation of genetically modified crops including cotton (Gossypium hirsutum), field corn (Zea mays), soybean (Glycine max), and canola (Brassica napus) with resistance to dicamba and 2,4-D herbicides has been developed to address the problem of glyphosate-resistant weeds. In the few years since their commercial introduction, these technologies have been rapidly adopted. The objective of this study was to determine the potential effects of simulated, single drift events of 2,4-D and dicamba on pecan (Carya illinoinensis) trees. 2,4-D amine [3.8 lb/gal acid equivalent (a.e.)] or dicamba-Diglycolamine salt (4.0 lb/gal a.e.) were applied in 1.0%, 0.1%, and 0.01% by volume spray solutions to pecan trees in June 2013. In 2016 and 2017, 2,4-D choline (3.8 lb/gal a.e.) or dicamba-N,N-Bis-(3-aminopropyl) methylamine (5.0 lb/gal a.e.) were applied in 1.0%, 0.1%, and 0.01% by volume spray solutions to pecan trees in May. These results suggest that serious injury can occur to pecan trees receiving a drift application of 1.0% by volume dicamba or 2,4-D. This injury includes deformed foliage, dead foliage, dead limbs, and/or branches, and arrested nut development. There were no major differences in the response of pecan to either dicamba or 2,4-D at similar rates in this study. Pecan damage resulting from off-target movement of 2,4-D and dicamba at rates ≥1% by volume has the potential to cause significant injury. Yield was not negatively affected by any of the treatments, suggesting that pecan trees can compensate for the observed injury to some extent. The effect of treatments on percent kernel was variable.

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The effects of mechanical fruit thinning on pecan [Carya illinoinensis (Wangenh.) K. Koch] yield, nut quality, and profitability were assessed using ‘Sumner’ and ‘Cape Fear’ pecan trees cultivated in a commercial orchard. The moderate to light production year (OFF year) return crop and return crop value of ‘Cape Fear’ and ‘Sumner’ was increased by mechanical thinning in the year of high production (ON year). This enhanced the 2-year total value and 2-year average value of both cultivars. Increased profitability of these cultivars with mechanical fruit thinning results primarily from higher yields and prices in the OFF year of production, which offset any loss in yield and/or crop value generated by fruit thinning in the ON year. Premature germination of ‘Cape Fear’ pecans was reduced from 34% to 4% with mechanical fruit thinning. Mechanical fruit thinning appears to be a highly valuable practice, leading to increased profit potential for ‘Cape Fear’ and ‘Sumner’ pecan.

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