Pecan Production Research Articles

Pecans and Hurricanes

gradually weakened while moving up the Cumberland Plateau and across the Appalachian Mountains before reentering the North Atlantic on 21 Aug. This single storm greatly damaged the state’s pecan industry and totally eliminated its tung industry (Kilby and Converse, 1970). Pecan nut production in Mississippi in 1970, the year after the storm, was only ≈27% of the average of that for the previous 5 years. A similar situation also occurred in Alabama, also a Gulf Coast region with a long and violent history of hurricanes. In fact, 41 hurricanes hit the Alabama coast from 1559–1996 (Longshore, 1998). In recent years, these include Camille (1969), Eloise (1975), Frederic (1979), Elena, Danny, and Juan (1985), and Erin and Opal (1995). Frederic in 1979 had a profound destructive effect on Alabama’s pecan production, destroying ≈60% of the bearing trees in two counties that were responsible for ≈60% of the state’s total production. Opal, on 4 Oct. 1995, was especially destructive to the pecan industry, with 384 km·h winds near the coast and ≈80 km·h wind gusts throughout most of the state (Wood, 1996). As many as 50% to 80% of the trees in many counties were destroyed. Opal was the strongest hurricane to reach land in the Gulf of Mexico area during October in recorded history (Kimberlain and Elsner, 1998). South Georgia possesses the largest concentration of pecan production in the eastern United States, producing ≈30% to 40% of the U.S. crop in most years (U.S. Department of Agriculture, 1975–97; Wood et al., 1990). Although most of the pecan production zone within the state is 175–500 km from the Gulf Coast, and is relatively safe from the intense winds of hurricanes, most of the state’s industry is vulnerable to substantial damage from storms tracking across the region. The state had 69 hurricanes and 30 tropical storms from 1752 to 1995 (Longshore, 1998). Eleven of the hurricanes had intensities of Category-3. The most devastating to the Georgia pecan industry was the Great Mobile Hurricane, hitting the state’s orchards with 161 km·h winds in 1952 (Longshore, 1998). Degenerate hurricanes, such as tropical storm Alberto, which hit southwestern Georgia 3 July 1994, also can cause great damage to pecan orchards. Although wind speeds had diminished enough to merit classification as only a tropical storm by the time Alberto entered Georgia, ≈112 km·h wind gusts and ≈54 cm of rain within 24 h caused considerable tree, nut, and limb loss over a wide area of the state, as well as a once-per-500-year flood in southwestern Georgia when it stalled after colliding with an entrenched high pressure system over the southern United States (Longshore, 1998).

508 Studies on the Effects of Zinc Supply on Growth, Development, and Nutrient Uptake of Pecan Seedlings from Different Seedstocks

Zinc deficiency is a nutrient disorder that is observed in pecan production areas. In the field it is characterized by a rosette shoot habit and interveinal leaf chlorosis. Up to now, the induction of zinc deficiency has not been accomplishable in the field or greenhouse. Thus any critical evaluations of effects of zinc nutrition on tree growth and development have been lacking. A hydroponic culture system was developed where zinc deficiency was induced. Seedstocks collected from `Stuart', `Curtis', and `Wichita' trees were grown with and without zinc supply. Biomass, leaf area, node number, and visual symptoms were assessed. Foliar deficiency symptoms were rated 4 and structural evaluations were conducted using light and electron microscopy. Significant differences in visual symptoms were observed between treatments and among cultivars. Leaf area significantly decreased in `Stuart' and `Curtis' under zinc deficient conditions. Zinc had no significant effect on biomass and internodal length. Foliar nutrient contents were compared between cultivars. Our data suggest that genotypic differences in sensitivity to zinc deficiency exists and improving pecan production through genetic selection for zinc efficiency appears promising.

Pecan Production in the Northern United States

More than 93% of pecans [Carya illinoinensis (Wangenh.) K. Koch] produced in the United States are grown in the southeastern and southwestern states. However, the native range of the pecan tree extends northward into Kansas, Missouri, and Illinois. In these northern states, commercial pecan production is expanding as additional acres of native trees are brought under cultivation and orchards of short-season, cold-hardy cultivars are established. Native nut production dominates the northern pecan industry accounting for over 95% of nuts produced in the region. Cultural practices for native pecans have been developed for northern groves that feature low inputs and good yields. Pecan cultivars adapted to the north ripen their fruit in a climate that provides 155 to 200 frost-free days. Few generalizations can be made about northern cultivars. The nuts produced by these cultivars vary in size from small [4 g (0.14 oz)] to medium [8 g (0.28 oz)] with shelling percentages ranging from 44% to 59%.

A Model for Predicting Pecan Production under Arid Conditions at High Elevations

A multiple regression model (R2 = 0.945) was developed from historical data, 1971-92, to predict pecan [Carya illinoensis (Wangenh.) C. Koch] production in an arid climate at high elevations. Dependent variables were year of production as a measure of production trend, number of degrees below 0.6°C following budbreak as a measure of late spring freeze injury, and number of degrees below 0.6°C preceding nut maturity as a measure of early fall freeze injury. Year of production was the dominant factor influencing production. Freezing temperature following budbreak had about two times more effect on production than freezing temperature preceding nut maturity. Pecan production under arid conditions at high elevations depends on fewer variables (three) than previously shown for humid conditions (eight variables).

A Climatic Model for Pecan Production under Humid Conditions

A multiple regression model was developed from historical data, 1945-92, to predict pecan [Carya illinoensis (Wangenh.) C. Koch] production in a humid climate. Variables were production trend (year of production), previous year's production, and climatic indices for the previous and current year. Production trend was used to measure change in production with time. Previous year's production was the index of alternate bearing. Variables for previous year's climate were heating degree-days for April-October and cumulative rainfall during May-July and 1-15 Sept. Variables for current year's climate were cumulative rainfall during April-August and 1-15 Sept. The indicator used for scab [Cladosporium caryigenum (Ell. & Langl.) Gottwald] infection was the highest cumulative sum of 2 or more days of consecutive rain occurring in May, June, or 1-15 July. The R2 for the model was 0.908. Production trend was the most important factor influencing production during the 1945-92 study period. Importance of the other variables in decreasing order were previous year's rainfall in May-July, consecutive rainy days, previous year's production, current year's 1-15 Sept. rainfall, previous year's heating degree-days, previous year's rainfall for 1-15 Sept., and current year's rainfall during April-August. Previous year's conditions had a greater effect on production than current year's. The recent decline in pecan production in the southeastern United States is due to an unfavorable change in climate.

Pecan Production Trends: A Comparison of Production in the Southeastern and Southwestern United States

The United States pecan industry experienced dynamic production changes during the last 25 years. Production in Georgia, the leading state, experienced serious problems during the late 1980s and early 1990s as a result of orchard crowding, old orchards, high incidence of diseases, and other problems. During the same 25-year period, plantings and production shifted to the southwestern United States to new production centers in Texas, New Mexico, Arizona, and California under a drier, more-favorable growing environment. Although the southeastern region continues to lead the nation in annual pecan production due to the high number and concentration of orchards with improved varieties, production in the southwestern region eventually may dominate the industry.

A CONTAINERIZED METHOD OF SCREENING FOR RESISTANCE TO ROOT ROT CAUSED BY PHYMATOTRICHUM OMNIVORUM

Phymatotrichum Root Rot, caused by Phymatotrichum omnivorum (Shear) Duggar, imposes severe losses upon dicotyledonous horticultural crops in the southwestern United States and northern Mexico. Rootstock resistance could benefit pecan (Carya illinoensis) production in affected growing areas; however, erratic growth habit of this pathogen and site variability prevents effective field screening. We have developed a containerized screening method for horticultural crops, using a commercial soilless growing medium. In sterile cultures, 2.5 × 60 cm glass tubes containing Metro Mix 500 yielded more grams of P. omnivorum sclerotia than cultures grown in Houston Black Clay, a traditional medium for cotton research. Preliminary screening with Okra (Abelmoschus esculentus) in non-sterile Metro-Mix 500 resulted in 75% mortality of inoculated plants in 30-35 days. Preliminary screening with 12-week-old, open-pollinated `Apache' and `Moore' pecan rootstocks has resulted in 25% mortality of inoculated plants in 150 days. Pecan seedlings with visible taproot infection appear to delay mortality by adventitious root formation.

IS PECAN PRODUCTION BEING LIMITED BY INSUFFICIENT SUNLIGHT?

Observations of net assimilation rates (`A') by pecan sun and shade leaves in relation to various levels of solar irradiation, the light adaptation characteristics of these leaf types, the role of clouds in suppressing the penetration of solar irradiation, and the abundance of cloud cover in the southeastern U.S. during the growing season, suggest that nut production throughout the U.S. pecan belt is being limited by insufficient sunlight with the southeastern U.S. (comprising about 2/3 of the commercial U.S. pecan production) being especially impacted. In support of this hypothesis, regression analysis showed cultivar-type nut production for Georgia from 1977-1989 to be significantly (P<.0001, R2 = 0.79) associated with sunlight levels ≥ 3000 Wh m-2d-1 from mid August to early October for the same year. This is taken as evidence that the amount of sunlight reaching the canopy seems to be a major factor that should be considered in relation to orchard site selection and canopy management techniques.

PECAN TREE GROWTH, PRODUCTION, AND NUT QUALITY RESPONSES TO WATER STRESS

Pecan tree (cv. “Western Schley”) water stress was numerically quantified with the crop water stress index (CWSI). The CWSI was used to schedule irrigation at increasing water stress levels to correlate the effects of water strees on tree growth, production, and nut quality from 1987 to 1989. Highest growth increases, production, and nut size were attained at lower water stress levels (CWSI = 0.08 to 0.14 units). Even moderate increases in water stress (CWSI>0.20 units) decreased pecan tree growth and production, and significantly reduced nut size (P=0.01). A significant difference (P=0.05) in nut quality was measured only in 1988. Depending on yearly climatic variation, the amount of irrigation water required to maintain the CWSI below 0.14 units in the same orchard varied 44% over three years. The CWSI is a viable tool to assess pecan water stress.

Energy Drain by Three Pecan Aphid Species (Homoptera: Aphididae) and Their Influence on In-shell Pecan Production

An estimate of the energy requirements of the three species of aphids, Monellia caryella (Fitch), Monelliopsis pecanis Bissell, and Melanocallis caryaefoliae (Davis), that feed on pecan, Carya illinoensis (Wangenh.) K. Koch, indicated that during a lifetime, an individual of M. caryella consumes 8.4-fold more energy (301 J) than that of M. pecanis (36.1 J) and ca. 7-fold that of M. caryaefoliae (44.8 J). When expressed as an average-age individual typical of a season-long field population, M. caryella extracts ca. 8-fold more energy than M. pecanis or M. caryaefoliae . Most energy consumed by all three species was excreted as honeydew. Growth efficiency was low for all three species, but was highest for M. caryaefoliae (25%), followed by M. pecanis (19%) and M. caryella (5%). Regression models were derived to estimate the cumulative level of energy consumed by aphids of various ages for growth, respiration, excretion, and total energy removal. Determination of the season-long standing-aphid population (and aphid-days) in two different aphid management programs within a 70-yr-old ‘Stuart’ pecan orchard and influence of these populations on nut yield indicated that all three species are highly detrimental to nut production; extraction of 1 × 106 J, via feeding by M. pecanis or M. caryella , reduced in-shell nut production by 58.7 g per 70-yr-old ‘Stuart’ tree. A season-long standing population of one individual of M. pecanis per leaf of such trees reduced in-shell nut yield by 2.41 kg; 18.13 kg was lost because of the same level of M. caryella .

Apparent Effect of Zinc Treatment on the Growth Rate of Pecan Production and Yield

Abstract Rosette was the major pecan [Carya illinoensis (Wangenh.) C. Koch] production problem prior to the discovery, in 1932, that the disorder was a symptom of Zn deficiency. A comparison of pecan production during the 10-year period prior to 1933 and the 10-year period following 1933 was made to determine the apparent effect of the use of Zn on the growth rate of pecan production from orchards in native and non-native pecan areas. Following the discovery of the cause of rosette, the rate of pecan production increased in non-native but not in native areas. The differential response is proposed to have been due primarily to less severe Zn deficiency in orchards in native than non-native areas. Alternatively, correction of Zn deficiency would have been less likely in native area orchards because of the general ineffectiveness of soil applications of Zn on calcareous soils.

‘Pawnee’ Pecan

Abstract ‘Pawnee’ pecan [Carya illinoensis (Wang.) K. Koch] is a precocious and prolific producer of high quality nuts. It was released by the USDA 2 Nov. 1984. Early maturity, large size, and high kernel percentage make the nuts of this cultivar uniquely suited for the early Thanksgiving and Christmas holiday market. Earlier nut maturity also makes ‘Pawnee’ a potential cultivar for the northern pecan production area where there are few protandrous cultivars from which a grower can choose.

Impact of Pecan Weevil 1 on Pecan Production in a Pest-Managed Commercial Orchard 2

A study was conducted to quantify various types of damage caused by the pecan weevil in a pest-managed, commercial pecan orchard. The types of damage evaluated included premature nut drop, black spots on the kernel, shriveled kernels, and destruction of the kernel by larvae. Premature nut drop due to adult weevil feeding was the most prevalent type of weevil-induced damage observed in the study. Although the primary objective of the study was to quantify pecan weevil damage, it was observed throughout the study that the greatest percentage of nut loss occurred from nuts dropping prematurely for unknown reasons.

Relative Importance of Rising Energy Costs on Pecan Production Costs in Georgia vs. Arizona1

Abstract Cost analysis for production of pecans [Carya illinoensis (Wang.) K. Koch] under advanced management techniques indicate that rising energy costs will give a competitive advantage to a grove located in the lower coastal plain of the Southeast relative to one in the arid southwestern United States.

Cycles in U.S. Pecan Production 1919—1974 Identified by Power Spectral Analysis1

Abstract U. S. production of pecan (Carya illinoensis (Wang) K. Koch) has been characterized by highly irregular variations in crop size from season to season. Spectral analysis is applied to the U. S. pecan production system to identify cycles. In analysis of U. S. pecan production data for 1919 through 1974, a first order autoregressive process with a negative constant of −0.39 to −0.62, a biennial alternating process, was found. Also identified were cycles of 2½, 4, and 11 – 16 years statistically significant at the 95% and higher levels for all pecans, native pecans and improved pecans.

Shading Effect on Pecan by Sooty Mold Growth

The buildup of sooty mold fungus on the honeydew that is deposited on the upper surfaces of the foliage of pecan, Carya illinoensis (Wang) K. Koch, as a result of feeding by Monellia costalis (Fitch) and Monelliopsis nigropunctata (Granovsky) was measured throughout the growing season. The percentage reduction in light transmission by sooty mold was as high as 25%. Therefore, sooty mold could have a serious effect on pecan production.

Influence of Trellis Type on Yield of Muscadine Grape1

Abstract One-wire, 2-wire, and overhead trellis systems of the muscadine grape, Vitis rotundifolia, Mich., cv. Hunt, were compared for 20 bearing years. Initially, plants trained to the 2-wire trellis had the highest yield; but for each of the next 18 years, the highest yield was obtained from the overhead trellis. All training systems exhibited alternate bearing after the 7th crop year. The alternate bearing pattern was the same as the state pecan production.

The Consumer Market for Pecans and Competing Nuts

Pecans contribute significantly to agricultural income in Georgia and in several other Southern states. Eleven Southern states produce the total U. S. commercial supply of pecans and during the years 1967-69, the average annual farm value of marketings was nearly $74 million. Georgia is the leading state in pecan production, contributing 27 percent of total U. S. production and 31 percent of total market value during this three-year period. Georgia produced 60 million pounds of pecans annually with an average 1967-69 farm value of over $23 million.

Pecan Industry in the United States

' HE pecan tree and its fruit have become important factors in man's way of life in southern and southeastern United States. The pecan tree is native to much of the region, but not all. In its native habitat it has developed from an the spot food for Indians, early explorers, and pioneers to the source of a significant industry, and in recent years the industry has spread to adjacent regions. (Figures 1 and 2.) Beginnings of the industry were small scale with negligible alterations in patterns of life and landscape. Before 1900 wild nuts were gathered irregularly from time to time as convenience permitted, and were consumed at home or sold locally in conformity to a fluctuating market. Later, when inhabitants of the region began to realize that the nut crop might have permanent commercial value, they became planters as well as gatherers and consumers. With aid of express and mail orders, nuts were sold, first to peripheral areas in proximity to the producing regions, and later to large city markets in more distant regions. When planting of improved varieties of trees became prevalent and pecan production began to take on characteristics of a productive industry, the pattern of life and the cultural landscape of the region were altered. Until that time, man's only interest was in nondescript, scattered pecan trees he found growing wild. Now he became interested in growing homogeneous, well-kept orchards, with real commercial value. As a result, the avocation of nut gathering became a vocation for many people of the area, and the pecan industry became firmly established.