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Typical damage, cleanup, and recovery from four ice storms beginning in Dec. 2000, with the latest in Dec. 2007, are reported for pecan (Carya illinoinensis). Damage levels were amplified as radial ice accretion increased. Cultivar affected the amount of damage incurred. Trees less than 15 ft tall typically had the least damage. Trees 15 to 30 ft tall incurred as much or more damage than larger trees and cleanup costs were greater. Production potential was directly related to canopy loss during the first growing season. The time to recover full production potential varied with the severity of canopy loss. Cleanup costs depended upon the amount of canopy damage incurred, tree spacing, tree size, and the amount of pruning needed to remove hanging and damaged limbs from the tree.

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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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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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Response from foliar-applied P (0.0%, 0.50%, 0.75%, or 1.00% P from KH2PO4) was compared to that from root-supplied P (Hoagland's solution) in pecan [Carya illinoinensis (Wangenh.) C. Koch] seedlings. Compared with no applied P, foliar-applied P suppressed or prevented P deficiency symptoms; increased the P concentration in the leaf, trunk, and root; and increased tree growth. However, P in all 3 organs and growth of plants treated with foliar sprays were less than for plants with root-supplied P. Furthermore, P sprays eventually produced leaf scorch. Compared to root-supplied P, omitting P affected N, P, K, Ca, Mg, Fe, Mn, B, Cu, Zn, Na, and Al in the plant. These imbalances induced by P deficiency were only partially alleviated by foliar-applied P.

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Each of 11 insecticides tested as a single spray application on mature leaves of pecan [Carya illinoinensis (Wang.) K. Koch] seedlings reduced net photosynthesis (Pn) 1 day after treatment. Eight of these materials still reduced Pn 9 days after a single spray treatment; however, in a study with 5 materials, all seedlings except those treated with petroleum oil had recovered after 14 days. Recovery of leaf photosynthetic activity generally occurred more rapidly following application of wettable powder formulations than emulsifiable concentrates. Petroleum oil was the most damaging treatment with Pn of treated plants being only 60% of the untreated check 9 days after treatment; however, leaves were nearing recovery after 14 days. The influence of insecticides on pecan irregular bearing is discussed.

Open Access

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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Newly planted pecan (Carya illinoinensis Wangenh. C. Koch cv. Kanza) trees were grown for 5 years in a bermudagrass [Cynodon dactylon (L.) Pers.] sod with vegetation-free circles 0, 0.91, 1.83, 3.66, or 7.32 m in diameter. Trees were irrigated and fertilized to minimize growth differences associated with competition from the bermudagrass. There were no differences in trunk diameter among treatments the first 2 years of the study. During the next 3 years, trunk diameter increased curvilinearly as the vegetation-free circle increased. A vegetation-free circle diameter of 1.83 m produced near maximum tree growth. Although trunk diameter improved slightly as the vegetation-free diameter was increased up to 7.32 m, it was not sufficient to justify the additional expense for herbicides nor exposure of unprotected soil to erosion.

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Pecan [Carya illinoinensis (Wangenh.) K. Koch] trees exhibit nickel (Ni) deficiency in certain orchard situations. The symptoms are manifest as either mouse-ear or replant disorder and in certain situations are associated with nematode parasitism. A field microplot study of pecan seedlings treated with either Meloidogyne partityla or Criconemoides xenoplax or both found that parasitism by M. partityla can result in enhancement in the severity of mouse-ear symptoms and a reduction in foliar Ni concentration. The Ni threshold for triggering morphological symptoms in young developing foliage was between 0.265 and 0.862 μg·g–1 dry weight, while the threshold for rosetting was between 0.007 and 0.064 μg·g–1 dw. Results indicate that parasitism by M. partityla is a contributing factor to the induction of Ni deficiency in pecan and raises the possibility that nematode parasitism and Ni nutrition can be contributing factors to many plant maladies.

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Measurement of nutrients in leaf tissue is a practical method of monitoring the nutritional status of perennial crops such as pecan (Carya illinoinensis, Wang. C. Koch). Accurate interpretations require known standard concentrations for the crop and region. To determine standard concentrations for pecans, focusing on those grown in the desert southwest, we conducted a survey of 135 `Western Schley' pecan trees in Arizona for 2 years. Leaf nutrient concentrations and yield were collected for each tree. Leaf nutrient concentrations from the highest yielding trees (50th yield percentile) were used to calculate a mean and CV for each nutrient. Results were compared with data from New Mexico, Georgia, and Sonora, Mexico. Relatively large differences were noted in mean K, Ca, B, Cu, Fe, Mn, and Zn levels. Nutrient interpretation ranges were calculated based on Arizona population statistics using the balance index method.

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Xylella fastidiosa Wells et al., the pathogen that causes pecan [Carya illinoinensis (Wangenh.) C. Koch] bacterial leaf scorch disease, was demonstrated to be highly transmissible through graft unions from infected rootstock into new growth developing from scions. Infected rootstocks were obtained by inoculation of pecan seedlings in pots with in vitro cultures of the pathogen. If rootstock infection occurs in nature, transmission of the pathogen into tissue growing from scions could serve as a significant source of introduction of the disease into pecan orchards. Because symptom development in infected trees typically begins in midsummer and grafting takes place in the early spring, it would be difficult to identify infected rootstock before grafting. Commercial pecan growers sometimes attempt to eliminate bacterial leaf scorch from trees by regrafting to other cultivars. The high rate of transmission from infected rootstocks observed in this test and the lack of knowledge of cultivars with resistance to the disease makes this practice ineffective.

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