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- Author or Editor: Michael T. Smith x
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.
A 4-year field study on pecan [Carya illinoinensis (Wangenh.) K. Koch] provided indirect support of the supposition held by some U.S. pecan growers that air-blast foliar sprays of potassium nitrate (KNO3) plus surfactant enhances nut yield. While these treatments did not measurably influence yield components, foliar K nutrition, or net photosynthesis, they did suppress “yellow-type” aphid populations. While air-blast sprays of water alone suppressed aphid populations, the inclusion of KNO3 plus surfactant provided an additional level of suppression.
Whole fruit clusters of `Pawnee' pecan [Carya illinoinensis (Wang.) C. Koch.] were collected from three shoot types: terminal and lateral shoots without a secondary growth flush and shoots that had an early-season secondary growth flush. Fruit per cluster were counted and nuts were individually harvested, weighed, shelled and graded. Bloom the following year was determined for the same shoots where clusters were collected. Wafers (cotyledons that failed to develop) were not associated with cluster size or shoot type. When wafers were included in the data, nut weight, kernel percentage and return bloom were not affected by cluster size or shoot type. However, when wafers were excluded from the data there were significant relationships of cluster size and shoot type with the dependent variables. Cluster size on lateral shoots was negatively related to nut weight and kernel percentage. Cluster size on terminal shoots without a secondary growth flush was inversely related to kernel percentage, but not related to nut weight. When shoots had a secondary growth flush, cluster size was not related to kernel percentage or nut weight. There was a positive linear relationship between cluster size and total kernel weight for the three shoot types. Return bloom of terminal shoots without a secondary growth flush was negatively related to cluster size, but cluster size did not affect return bloom of the other shoot types. The number of shoots that developed the following year was positively related to cluster size for terminal and lateral shoots, but not for shoots with a secondary growth flush. Shoots with a secondary growth flush produced substantially more shoots with larger fruit clusters the next year than the other shoot types.
Alternate bearing pecan trees [Carya illinoinensis (Wangenh.) C. Koch] were hand-thinned annually to 1, ≤2, or ≤3 fruit/cluster or not thinned when the ovule was about one-half expanded. Return bloom was monitored on (1) vegetative shoots, (2) bearing shoots without a second growth flush in the terminal position on 1-year-old branches, (3) bearing shoots without a second growth flush in the lateral position on 1-year-old branches, and (4) bearing shoots with a second growth flush that were primarily in the terminal position. Yield and nut quality were determined in addition to nonstructural carbohydrate, organically bound nitrogen (N), and potassium (K) concentrations in the roots and shoots during January. Fruit thinning improved return bloom but had little effect on weight/nut, kernel percent, or kernel grade. Fruit thinning had either a modest or no effect on nonstructural carbohydrates, organically bound N, and K concentrations. Vegetative shoots and bearing terminal shoots produced a similar number of flowers/1-year-old branch and percentage of flowering current-season shoots. Bearing lateral shoots produced fewer flowers than vegetative shoots most years and fewer flowering current-season shoots during one year. Shoots with a second growth flush produced more flowers/1-year-old branch and a larger percentage of flowering current-season shoots than did vegetative shoots 2 of 3 years. These data indicate fruit thinning of overloaded trees improved return bloom, but the lack of interactions between thinning treatment and shoot type suggests that the number of fruit/cluster was less important than total crop load in determining nut quality and return bloom. Thus removal of entire fruit clusters appears as effective as thinning fruit within a cluster to maintain adequate nut quality and promote return bloom. Nonstructural carbohydrates, organically bound N, and K were not limiting factors in bearing consistency because they were not depressed in unthinned trees. Nonstructural carbohydrates, organically bound N, and K concentrations were not closely linked to alternate bearing because return bloom was enhanced by thinning, but thinning did not affect their concentrations.
The current theory of pecan [Carya illinoinensis (Wangenh.) C. Koch] alternate bearing is the “growth regulator–carbohydrate theory” in which flowering is first controlled by growth regulators produced by fruit and leaves, and then by the size of the carbohydrate pool near budbreak. Lack of nitrogen (N) reserves has also been proposed to be limiting after large crops, thus reducing return bloom. Annual production was determined for 12 individual trees for 3 years. Return bloom was monitored on four previous-season shoot types: 1) vegetative shoots, 2) bearing terminal shoots without a second growth flush, 3) bearing lateral shoots without a second growth flush, and 4) bearing shoots that were primarily in the terminal position with a second growth flush. Nonstructural carbohydrates, organically bound N, and potassium (K) concentrations were determined in roots and shoots. Regression analysis was used to determine the effect of yield on subsequent nonstructural carbohydrates, N, and K in the roots and shoots, and their postyield concentrations on subsequent flowering. Alternate bearing was evident because there were reductions of 18%, 16%, and 18% in the percentage of current season shoots flowering for every 10 kg/tree production increase in the previous season's yield in 2002, 2003, and 2004 respectively. Flower production in 2002 decreased by 2.6 flowers/1-year-old branch and 1.6 flowers/1-year-old branch in 2003 for each 10 kg/tree increase in production. The third year of the study, neither previous season shoot type nor yield affected subsequent flower production. The previous year's shoot type did not affect the percentage of current season shoots flowering; however, the previous year's shoots that had a second growth flush produced more flowers the following year than the other shoot types. Results suggested that crop load was not related to nonstructural carbohydrates, N, or K in the roots and shoots during January in these well-managed trees. Stored nonstructural carbohydrates, N, and K were also not related to return bloom. These data suggest that the current “growth regulator–carbohydrate theory” may not be valid in these well-managed trees. Nonstructural carbohydrates, K, and organically bound N do not appear to be critical factors regulating flowering.
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.
Trees with about the same crop load were hand thinned to 1, <2, or <3 fruit per cluster or not thinned while the ovule was about one-half expanded. Treatments were replicated three times. Vegetative, and bearing terminal, lateral and shoots with secondary growth were tagged in October, and flowering was determined the following year. Shoots and roots were sampled during dormancy and analyzed for organically bound N, and K. Results indicated that branches with secondary growth produced substantially more shoots and flowers than other branch types. The unthinned trees produced fewer total flowers per branch, had a lower percentage of branches with flowering shoots, and smaller flower clusters than thinned trees. Organically bound N in the roots and shoots was not affected by crop load. Crop load appeared to be negatively related to K concentration in roots <1 cm in diameter, but not in roots >1 cm in diameter. The data suggest that neither N nor K were limiting in trees with large crops.
Whole fruit clusters were collected from three shoot types: terminal and lateral shoots without secondary growth, and shoots with secondary growth. Fruit per cluster was counted and nuts were individually weighed, shelled and graded. Return bloom of the same shoots was measured. Results indicated that cluster size of lateral bearing shoots was negatively related to next year's average kernel weight, nut weight, and kernel percentage. However, only kernel percentage was related to cluster size on terminal bearing shoots, and none of these parameters were related to cluster size on shoots with secondary growth. Cluster size and total kernel weight per shoot were positively related for the three shoot types. Return bloom of terminal shoots was negatively related to cluster size, but cluster size did not affect return bloom of the other shoot types.
The most significant horticultural problem facing pecan producers is alternate bearing. Four pecan [Carya illinoinensis (Wangenh.) C. Koch] cultivars were chosen, two with low to moderate and two with severe alternate-bearing tendencies, to compare selected characteristics related to irregular bearing. The cultivars were Colby and Peruque (low to medium alternate-bearing tendency) and Osage and Giles (high alternate-bearing tendency). Vegetative shoots and fruit-bearing shoots in the terminal and lateral position on 1-year-old branches were tagged in October, and flowering was determined the next spring. Shoot and root samples were collected while dormant and then analyzed for organically bound nitrogen (N), potassium (K), and nonstructural carbohydrate concentrations. As expected, ‘Colby’ and ‘Peruque’ had a lower alternate-bearing tendency than ‘Giles’ and ‘Osage’. Cultivars with a low alternate-bearing tendency had a larger return bloom on the bearing shoots in the terminal position than the other shoot types. Cultivars with a high alternate-bearing tendency had a lower return bloom on bearing terminal shoots than vegetative shoots. Bearing shoots in the lateral position usually had a lower return bloom than the other shoot types regardless of cultivar. Neither root nor shoot N, K, or nonstructural carbohydrate concentrations appeared to be closely related to the alternate-bearing characteristics of the four cultivars. The unique characteristic identified for low alternate-bearing cultivars was their ability to produce as many or more flowers and flowering shoots the next year on previously bearing terminal shoots compared with previously vegetative shoots. In high alternate-bearing cultivars, return bloom of bearing terminal shoots was suppressed relative to their vegetative shoots.