Pecan [Carya illinoinensis (Wangenh.) K. Koch.] kernel necrosis is a malady characterized by development of a dark necrotic area at the basal end of the kernel. This problem is particularly severe on ‘Pawnee’ at some locations during certain years. Currently, the cause of kernel necrosis is not known. Initially, this problem appeared confined to certain cultivars in a north Texas orchard in the Red River Basin and ‘Oklahoma’ in a central Oklahoma orchard adjacent to the Deep Fork River. After El Paso, TX, producer reports of an unknown problem on ‘Pawnee’, mature nuts from orchards near El Paso, north Texas, and southern, central and northeastern Oklahoma were evaluated for kernel necrosis. Kernel necrosis was abundant on ‘Pawnee’ nuts from El Paso and southern Oklahoma, moderate at the north Texas site, and at low levels in one northeastern Oklahoma orchard. None was found in two ‘Pawnee’ orchards, one in central Oklahoma and the other in northeastern Oklahoma. In another study, yield was monitored on hedge-pruned ‘Pawnee’ pecan trees over a 5-year period to determine the relationship with kernel necrosis. The incidence of kernel necrosis was greater when yield was less. A third study sampled nuts from the lower and upper one-third of canopies from randomly selected trees varying in trunk size. Kernel necrosis frequency was similar in the upper canopy among different trunk sizes, but the incidence in the lower tree canopy decreased as trunk size increased.
Michael W. Smith
Yield and selected nut quality characteristics were monitored on hedge pruned ‘Pawnee’ pecan [Carya illinoinensis (Wangenh.) K. Koch.] trees over a 5-year period to characterize optimum production defined as equal crops 2 successive years. Previous year yield was linearly or quadratically related to current-season yield in three of four instances. Optimum yield ranged from 18 kg/tree to 29 kg/tree among years. Weight/nut, weight/kernel, and percent kernel were negatively related to yield/tree. Weight/nut and weight/kernel were more closely related to yield/tree than percent kernel, indicating that as cropload increased, shell weight and kernel weight were disproportionately affected. Increasing croploads reduced kernel weight more than shell weight, thus reducing the correlation between percent kernel and yield. Twenty-seven percent of the trees in the study produced greater than average yields with a lower than average alternate bearing index.
Michael W. Smith
Thirty-five-year-old `Hayes' and `Patrick' trees (22 trees/ha) were fertilized with 112 kg N/ha (NH4NO3) either the second week of March or the first week of Oct each year. Phosphorus was applied (broadcast) during March 1986 and again during May 1989 at 0 or 244 kg P/ha. Treatments were arranged in a split-split-plot design with four single-tree replications. Leaf N concentration and the number of shoots/1-year-old shoot were not affected by N application time, and the effect on shoot length was inconsistent. Total yield and annual yield three of five years were greatest from `Hayes' when N was applied during Oct rather than March. Yield of `Patrick' was unaffected by time of N application. Phosphorus application increased soil P up to 20 cm deep, and leaf P concentration was increased three of five years in `Hayes' and two of five years in `Patrick'. Shoot growth, number of new shoots, nut size, kernel percentage, and yield were generally not affected by P application.
Michael W. Smith
Potassium (K) and phosphorus (P) partitioning were characterized in bearing pecan [Carya illinoinensis (Wangenh.) K. Koch] trees at selected times of the year during three successive years. The first-year trees had little to no crop, followed by a small crop the second year, and a near optimal to excess crop during the third year. Trees bearing a large crop accumulated more K and P in July than trees with little or no crop. K and P content in trees increased from budbreak until July, and then decreased until budbreak the following year. Allocation patterns of K and P among tree components changed during the growing season, with the greatest changes occurring in the annual plant parts. Results indicate that leaves were the principal source of labile K and P for developing fruit. A rapid accumulation of K in the fruit with a concurrent loss from leaves started in July when fruit began a rapid volume increase that continued during carbohydrate deposition in the cotyledon. At first, detectable shuck split K transported to the fruit ceased, but leaf K was partially replenished, presumably from K in perennial tissue because total tree K was static or decreased slightly. In contrast, rapid P transport to fruit began after fruit expansion while cotyledons were developing, presumably associated with oil synthesis and after initial shuck split for storage. Leaf P content continued to decline until leaves were killed by freezing temperatures in the fall. Data indicate that potentially large crops signal additional early season K and P absorption and accumulation in leaves and other tissue long before the fruit are strong K and P sinks. This suggests a complex signaling mechanism, essentially telegraphing a copious demand during the latter part of the growing season.
Michael W. Smith
Pecan [Carya illinoinensis (Wangenh.) C. Koch.] trees were injured by freezing temperatures in Oct. 2000, occurring about 4 weeks before the average first freeze and 6 weeks before the normal killing freeze (less than or equal to -2 °C). Nonbearing and bearing cultivars were rated for injury at four sites the following May. Nonbearing cultivars with little or no damage included `Caddo', `Clark II', `Giles', `Kanza', and `Peruque'. Those that had substantial damage included `Maramec', `Pawnee', `Oconee', `Shawnee', and `OK642'. Bearing cultivars with little or no injury included `Stuart', `GraKing', `Pawnee', `Tejas', and `Wichita'. The most severely damaged bearing cultivars were `Gratex', `Shoshoni', and `Squirrel's Delight'.
Michael W. Smith
Performance of peach trees at seven spacings were evaluated over an 8-year period. Treatments were `Garnet Beauty' on Lovell spaced 3.0 or 4.6 × 6.1 m and 4.6 or 6.1 × 7.6 m, self-rooted `Garnet Beauty' spaced 1.0 × 6.1 or 7.6 m then thinned to 3.0 × 6.1 or 7.6 m 4-years after planting, and self-rooted `Garnet Beauty' spaced 1.0 × 2.0 × 5.5 m managed as a meadow orchard with alternate rows pruned to 30-cm height after harvest. Trees spaced 4.6 × 6.1 m or closer were mechanically hedged beginning 4-years after planting to 9 m tall and 6 m wide. Trees in all treatments, except 1.0 × 2.0 × 5.5 m, were trained to an open-center and hand-pruned annually. Trunk area and canopy area of trees spaced 3.0 × 4.6 m or closer were smaller than trees in other spacings by 5-years after planting. Cumulative yield per ha of trees spaced 1.0 × 2.0 × 5.5 m was greater than yield from other spacings 2- through 4-years after planting, then less 6- and 7-years after planting. There were no significant differences in yield/ha among the other spacing treatments. Fruit size was not affected by treatment. Yield efficiency of trees spaced 3.0 or 4.6 × 6.1 m decreased by 8-years after planting compared to trees spaced 4.6 or 6.1 × 7.6 m, indicating a reduction in fruit bearing growth. Hand pruning time was proportional to tree spacing.
Michael W. Smith
Trees in a native pecan [Carya illinoinensis (Wangenh.) C. Koch.] grove vary in size, age, and genotype and tree spacing pattern is not uniform. This presents some problems for managing tree density, calibrating pesticide sprayers, and other management tasks. Trunk and canopy diameters and tree height of diverse sizes of native pecan trees in managed groves were measured and the relationships of cross-sectional trunk area with canopy footprint, surface area, and volume were determined. The canopy footprint, surface area, and volume per hectare were then calculated for the recommended stocking density of 6.9 m2·ha−1 of cross-sectional trunk area. Cross-sectional trunk area was strongly correlated with canopy footprint, surface area, and volume. Groves with an average tree size between 0.02 and 0.75 m2·ha−1 cross-sectional trunk had ≈50% canopy cover per unit land area and 3 ha·ha−1 bearing surface per unit land area at the recommended stocking density.
Michael W. Smith
Several new management tools and management practices are being developed for pecan. Major insect pests of pecan are pecan nut casebearer, hickory shuckworm, and pecan weevil. Sex pheromone attractants are being developed for each of these pests that improve monitoring. Also, a pecan weevil trap (Tedder's trap) was introduced recently that is more sensitive to weevil emergence than the previous trap. New models that predict critical periods for pecan scab infection are being tested. Certain legume ground covers are being tested to increase beneficial arthropods in the orchard for aphid control, and to supply N. Mulches are being investigated as an alternative to herbicide management for young trees. A mechanical fruit thinning method has been developed that increases fruit quality and reduces alternate bearing as well as stress-related disorders.
Michael W. Smith and Bruce W. Wood
Allometric equations were developed for orchard-grown pecan [Carya illinoinensis (Wangenh.) C. Koch] trees. Trees, ranging in size from 22 to 33 cm in trunk diameter 1.4 m above the ground, were destructively harvested from two sites. The entire aboveground portion of each tree was harvested and then divided into leaves, current season's shoots, and branches ≥1 year old plus trunk. Roots were sampled by digging a trench beginning beneath the trunk and extending to one-half the distance to an adjacent tree, then separating the roots from the soil. Roots were then divided into those less than 1 cm in diameter and those ≥1 cm in diameter. Equations in the form Y = eaXb were developed to estimate dry biomass of most tree components and the whole tree, where Y is the dry weight, e is the base of the natural logarithm, X is the trunk diameter at 1.4 m above the ground, and a and b are coefficients. A linear equation provided the best fit for estimating the weight of the current season's growth. Power equations were also developed to estimate the weights of inner bark and wood for different size trunks or branches.
Margaret E. Wolf and Michael W. Smith
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.