Progress 11/01/08 to 10/31/13
Outputs
Progress Report Objectives (from AD-416): 1. Provide improved horticultural tools for stabilizing pecan nut yields in alternate bearing pecan trees and orchards. 2. Develop an improved approach for orchard management of fungal diseases attacking developing fruit, based on enhancement of the tree's natural disease resistance mechanisms. Approach (from AD-416): Objectives are achieved via research and development efforts to introduce to commercial pecan producers new horticultural tools to improve production efficiency of commercial enterprises. The approach focuses on alternate bearing and pecan scab disease via introduction of the following tools: a chemical-based thinning strategy for regulation of crop-load; regulation of flowering and alternate bearing via plant growth regulators; an improved �conceptual tool� for managing alternate bearing; reduction of chemical stresses by improved nutrient element management with emphasis on zinc; and induction of greater natural tree resistance to fungal disease pests (such as pecan scab) via improved tree nutrition and systemic acquired resistance inducers. The approach includes numerous lab, greenhouse, and field based studies, but with a great deal of emphasis on field evaluation of treatments in real-world commercial orchard situations. Extension specialists are included in the research efforts to facilitate transfer of knowledge, strategies, and technologies to farmers. The approach largely relies on adaptation of existing technologies to pecan horticulture, but with new technology potentially being introduced for transition and inner-transition metals, and registration of existing commercial products for usage on pecan. There will be dozens of research studies conducted, with experimental designs structured to test hypotheses associated with objective-linked postulates. Results will be disseminated to scientific, extension, and commercial individuals and groups via appropriate publications/articles, talks, and field-days. This project has spanned its 5-year cycle and is transitioning to a new Project Plan on �Mitigating Alternate Bearing�. The ability for growers to manage alternate bearing by individual trees has been advanced by a) developing a mechanized hedge pruning protocol for the southeastern U.S., b) gaining an understanding as to how to better regulate flowering using gibberellic acid to reduce excessive cropping in the following year; by managing tree canopy health to maximize dormant season sucrose reserves, c) improving tree access to rare-earth elements, d) using plant bioregulators to prevent induction of alternate bearing by canopy damaging by black pecan aphids. A new theory was advanced for flowering regulation in temperate zone trees, with timely regulation of tree hormones increasing or decreasing subsequent year flowering with ethylene and cytokinins being especially promising for future study. New trace element tools were developed for improving crop nutrition by improving nickel and rare-earth element nutritional physiology. Management strategies and tools were developed for reducing June-drop and water- stage fruit-drop by improving tree boron, nickel, and potassium nutrition. It was also found that pecan, and most hickory species, are hyper- accumulators of rare-earth elements and likely possess a physiological requirement for one or more rare-earth elements as either essential or beneficial nutrient elements; thus, identifying management of organic matter in orchard soils as a means of ensuring that trees receive sufficient rare-earths to meet nutritional needs. These elements appear to help trees to better withstand water stress and adaptation to dry sites. It was found that improving tree nickel nutrition increases nutmeat quality, reduces crop loss to pecan scab disease and water-stage fruit-drop. Improving tree potassium nutrition was found to reduce �June drop�. Efforts to mitigate alternate bearing by reducing pecan scab found that phosphite is very effective at protecting trees from scab, especially that of foliage, and that the agent triggers a form of systemic resistance to scab. A screening of many other systemic resistance-inducing agents effective in other crops had no activity in pecan. Several co-dominate genetic markers, and other dominate genetic markers, were developed as tools enabling detailed investigation of the genetic diversity of the scab pathogen. Use of these markers indicate that there is far more genetic diversity in the pathogen than thought; therefore, leading to new orchard management approaches for managing scab resistance to fungicides and disease epidemics. An improved disease rating scale was developed that greatly improves visual estimation on disease severity. The above knowledge, tools, and strategies promise to greatly facilitate efforts by U.S. farmers to produce pecans. Accomplishments 01 Excessive iron triggers nickel deficiency. Nickel deficiency not only influences alternate bearing by pecan trees, but also reduces yield and quality of many other crops. Factors affecting the cellular bioavailability of nickel in either plants or animals have the potential to influence the health, yield and quality of plant and animal products. ARS researchers at Byron, Georgia, found that nickel deficiency is easily induced by excessive iron fertilization or plant exposure to iron, with iron acting in an antagonistic manner in regards to nickel bioavailability and nutritional physiology. This research identifies an important micro-nutrient interaction in plants that has heretofore been unrecognized, while possessing many practical applications in agriculture. For example, it identifies iron fertilization as a means of alleviating nickel toxicity in crops, especially those growing on highly mineralized serpentine soils. It also highlights the possible existence of iron induced nickel deficiency occurring in many cropping systems where iron is a fertilizer supplement. 02 Reducing pre-harvest germination (Vivipary) of pecan. Pecan crop loss to the germination of nuts while still on the tree (i.e., vivipary) is a major problem for many pecan farmers, especially those in hot arid climates. There is need to develop management strategies that stabilize year-to-year variability in marketable nutmeat yields due to vivipary. ARS researchers at Byron, Georgia, found that vivipary is greatly influenced by tree exposure to moist soils with high nitrate nitrogen during the nutmeat filling stage of fruit development, and that the malady is regulated by the plant hormone, abscisic acid. Moist soils and high fruit nitrate prevents timely production of abscisic acid in developing seeds, which prevents seed dormancy. These findings also implicate copper and/or molybdenum deficiency as major contributing factors to vivipary through their influence on the activity of the key enzyme producing abscisic acid. This information enables pecan, and possibly grain farmers, to tailor crop management strategies to reduce loss to pre-harvest germination. 03 Plant and animal nickel nutrition influences the activity of ribonuclease enzymes. The metabolism of nitrogen is key to a multitude of primary and secondary metabolic reactions taking place in both plants and animals. While nickel is an essential trace element in plants and animals, relatively little is known about its metabolic or physiological roles. ARS researchers at Byron, Georgia, found that a key plant/animal enzyme involved in the recycling of nitrogen (Ribonuclease A, RNase A) within organisms functions as a urease enzyme in the presence of nickel. This research demonstrates that a non- metallo enzyme, RNase A, exhibits dual activity depending on the presence or absence of nickel, and identifies a possible new metabolic role for nickel in plants and animals. The presence of both RNase A and nickel in the spring sap of pecan trees indicates that this enzyme is likely important to the cycling of nitrogen during the early growth phase of many crop species; thus, potentially affecting alternate bearing by pecan trees as well as nitrogen and nickel nutrition management strategies of other crops, especially those exposed to urea fertilizers or transport nitrogen as urea. 04 Phosphite as a new tool for managing pecan scab. Due to the emergence of fungicide resistance in the scab pathogen (Fusicladium effusum) to certain classes of fungicides, there is need for alternative fungicide chemistries for managing this devastating disease. ARS researchers at Byron, Georgia, found that the simple inorganic molecule, phosphite, registered for use on certain other crops, was highly efficacious in controlling the pecan scab fungus. Phosphite is effective in reducing the disease on young trees as a trunk application, but not on older trees. This research led directly to the registration of phosphite products for use in pecan orchards as canopy sprays in the southeastern U.S. The addition of phosphite as an effective alternative fungicide in the pecan �disease management toolbox� enables growers to minimize the impact of scab and reduces the risk of fungicide resistance developing among existing fungicides used to manage scab. 05 Improving the accuracy and reliability of pecan scab assessment. Accurate and reliable methods to assess disease are critical to ensure high quality data for comparing treatments statistically, as is required by researchers, and for growers who may base management decisions on estimates of disease. ARS researchers at Byron, Georgia, have demonstrated that use of some older category-type scales produces data that has less agreement with actual values and poorer reliability compared to assessments made using the 0-100% scale. These results provide the basis for stakeholders (scientists, advisors and growers) to use a rating system that provides data with the highest possible accuracy and reliability, thereby minimizing the risk of error in databased decision-making. 06 Genetic diversity of pecan scab. The pecan scab pathogen is known to adapt to resistant cultivars of pecan, and knowledge of the pathogen�s genetics will provide a basis for improving resistance development in new cultivars to ensure resistance that is more durable. ARS researchers at Byron, Georgia have now screened a total of 130 SSR markers, and have developed an additional 5 UP-PCR marker and 10 RAPD markers that will be used in studies of genetic diversity, which will lead to improved management of available resistance genes and thus more durable scab resistance.
Impacts
(N/A)
Publications
- Bock, C.H., Cook, A.Z., Parker, P.E., Gottwald, T.R., Graham, J.H. 2012. Short distance dispersal of splashed bacteria of Xanthomonas citri subsp. citri from canker-infected grapefruit tree canopies in turbulent wind. Plant Pathology. 61:829-836.
- Bock, C.H., Van Den Bosch, F., Parnell, S., Wood, B.W., Gottwald, T.R. 2013. The effect of Horsfall-Barratt category size on the accuracy and reliability of estimates of pecan scab severity. Plant Disease. 97:797-806.
- Bock, C.H., Wood, B.W., Gottwald, T.R. 2013. Pecan scab severity-effects of assessment methods. Plant Disease. 97:675-684.
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Progress 10/01/11 to 09/30/12
Outputs
Progress Report Objectives (from AD-416): 1. Provide improved horticultural tools for stabilizing pecan nut yields in alternate bearing pecan trees and orchards. 2. Develop an improved approach for orchard management of fungal diseases attacking developing fruit, based on enhancement of the tree's natural disease resistance mechanisms. Approach (from AD-416): Objectives are achieved via research and development efforts to introduce to commercial pecan producers new horticultural tools to improve production efficiency of commercial enterprises. The approach focuses on alternate bearing and pecan scab disease via introduction of the following tools: a chemical-based thinning strategy for regulation of crop-load; regulation of flowering and alternate bearing via plant growth regulators; an improved �conceptual tool� for managing alternate bearing; reduction of chemical stresses by improved nutrient element management with emphasis on zinc; and induction of greater natural tree resistance to fungal disease pests (such as pecan scab) via improved tree nutrition and systemic acquired resistance inducers. The approach includes numerous lab, greenhouse, and field based studies, but with a great deal of emphasis on field evaluation of treatments in real-world commercial orchard situations. Extension specialists are included in the research efforts to facilitate transfer of knowledge, strategies, and technologies to farmers. The approach largely relies on adaptation of existing technologies to pecan horticulture, but with new technology potentially being introduced for transition and inner-transition metals, and registration of existing commercial products for usage on pecan. There will be dozens of research studies conducted, with experimental designs structured to test hypotheses associated with objective-linked postulates. Results will be disseminated to scientific, extension, and commercial individuals and groups via appropriate publications/articles, talks, and field-days. Chemical thinning: Inconsistency in efficacy when using ethephon or calcium hydroxide to fruit-thin requires an approach using indirect chemical thinning using gibberellins in �Off� years to reduce subsequent �On� year crop load. Alternate bearing: Flowering and alternate bearing are found to be regulated via �gibberellins-ethylene� vs. �auxin-cytokinins� balances, followed by level of carbohydrate reserves during vernalization and bud break. Research also examined the role a) of �resource switching� and its impact on flowering; and b) sugar composition of late winter xylem sap and intensity of sap flow. Zinc and nutrient element stress: Special isotopically labeled zinc was applied to enable determination of how foliar zinc moves within trees; thus, providing information for development of a better and cheaper means of controlling zinc nutrition. An investigation of the rare-earth composition of pecan and Carya species, found them to be hyperaccumulators, with one or more rare-earth elements likely playing a beneficial biological role. Pecan scab: Research was aimed at confirming the efficacy of foliar applied Ni at different concentrations, and for assessing the effect of phosphite and method and timing of phosphite (PO3) applications for reducing the impact of pecan scab on pecan yield. Both Ni and phosphite were efficacious against scab, providing additional outcomes for integrated management strategies of pecan scab. However, results showed that trunk applications of phosphite were not efficacious. Pecan scab: The distribution and severity of pecan scab in mature, tall pecan trees, was studied. There was more severe disease in the lower third of trees not receiving a ground-based application of fungicide, and although disease in treated trees is less severe in the lower third, it is similar in the upper third to non-treated trees. This indicates that tall trees need aerially-applied fungicide to manage disease in the upper canopy. Systemically acquired resistance (SAR) to pecan scab: Phosphite reduces scab severity compared to other SAR agents. Several potential SAR agents are being tested on both seedling and as trunk injections in mature trees under field conditions to investigate whether they can act as triggers for resistance to pecan scab. Scab resistance: The genome of the scab fungus was partially sequenced to identify simple sequence repeat (SSR) markers for assessing genetic diversity of the pathogen and guide scab management decisions, and for finding durable disease resistance. Six SSR-markers are now identified for studying genetic diversity. Scab resistance: Standard area diagrams improve accuracy and precision of disease assessments; thus, enabling better quality assessments, resulting in more reliable and accurate data on which to base decisions. Research compared rating scales to using the percent scale for disease assessments, and to identify the optimal number of standard area diagrams to use to assess pecan scab. Accomplishments 01 Nickel Reduces Pecan Scab in Orchards. Pecan scab can cause severe yiel loss when environmental conditions are conducive to epidemic development Furthermore, resistance to certain fungicides used by pecan growers to control the disease demands an integrated approach to disease management Field studies have previously demonstrated a small but significant effec of foliarly applied Ni at reducing pecan scab. ARS researchers at Byron, Georgia, tested a full range of Ni concentrations to optimize the application strategy. By optimizing Ni applications growers are better able to manage pecan scab in orchards and consequently reduce scab- associated crop loss; thus, adding a new tool to the scab management toolbox. 02 Phosphite as a New Tool for Managing Pecan Scab. There has recently bee emergence of scab resistance to certain classes of fungicides used to control this fungal disease in orchards; thus new, alternative fungicide chemistries are needed for controlling this devastating disease. ARS researchers at Byron, Georgia, found that a simple inorganic chemical, phosphite, registered for use on certain other crops, to be highly efficacious for controlling the pecan scab fungus and disease in orchard when applied as a foliar spray, but it was less effective as a trunk application. This research led to registration of phosphite products for use in pecan orchards and its use by pecan growers to manage scab and other diseases, which helps minimize the impact of the disease and also reduce the risk of fungicide resistance developing among existing fungicides used to manage scab. 03 Early Spring Sap Flow and Sucrose Content Predicts Subsequent Flowering Pecan Trees. There are key knowledge gaps in regards to the flowering a alternate bearing mechanism in pecan trees. ARS researchers at Byron, Georgia, found that flowering and crop load are tightly linked to the volume and the amount of sucrose within late winter and early spring sap flow from tree trunks. This information affirms the importance of previous season canopy management to maximize leaf health in order to ensure following year flowering. Orchards are being increasingly manage to ensure availability of high dormant season carbohydrate and sucrose reserves for completion of the final phase of floral development. 04 Improving Accuracy and Reliability of Pecan Scab Assessment. Pecan scab can cause severe disease on fruit and leaves, which leads to nut crop yield loss. Accurate and reliable methods to assess disease are critical to ensure high quality data for comparing treatments statistically, as i required by researchers, and for growers who may base management decisio on estimates of disease. ARS researchers at Byron, Georgia, developed a �standard area diagram set� that aides scab disease assessment on fruit, and which reduces error and variability in disease assessments, and are preferable to unaided assessments or using disease-category scales. Thes standard area diagrams are being used to ensure that consistently high quality data is being recorded when disease assessments are made. 05 Improving Canopy Health of Tall Pecan Trees. Growers are faced with challenges managing foliage health and scab disease in tall (> 55 feet) pecan trees. Ground-based sprayers may not provide sufficient coverage t reach the tops of tall trees, and aerially applied sprays can be costly. However, there is no information available on the distribution of scab, nor whether the essential nutrient element concentrations differ in tall pecan trees. ARS researchers at Byron, Georgia, found that disease is most severe in the lower third of trees receiving no fungicide; however, in trees receiving fungicide, disease is either less in the lower third the canopy, or the same as the upper third of the trees receiving no fungicide. Nutrient element concentrations are also typically less at th top of the canopy. This work identifies a need for growers to use aerially applied fungicides in severe scab years, and to aerial application of micronutrients. 06 Genetic Diversity of Pecan Scab. The ability of the pecan scab pathogen adapt to new pecan cultivars is unknown, but knowledge of the pathogen�s genetics will aid development of improved cultivars with durable resistance. ARS researchers at Byron, Georgia, have partially sequenced the genome of the scab pathogen to identify SSR markers to study its population genetics. A total of 60 SSR markers have now been screened, o which six have now been identified for using in studies of genetic diversity. Resulting information on the genetic diversity of the scab pathogen is critical to help guide decisions in managing scab resistance in pecan so as to ensure durable disease resistance in newly developed cultivars planted by growers in regions prone to scab epidemics.
Impacts
(N/A)
Publications
- Bock, C.H., Brenneman, T.B., Hotchkiss, M.W., Wood, B.W. 2012. Evaluation of a phosphite fungicide to control pecan scab in the southeastern USA. Crop Protection Journal. 34:58-65.
- Wood, B.W., Grauke, L.J. 2011. The rare-earth metallome of pecan and other Carya. Journal of the American Society for Horticultural Science. 136(6) :389-398.
- Wagle, P., Smith, M.W., Wood, B.W., Rohla, C.T. 2011. Response of young bearing pecan trees to spring foliar nickel applications. Journal of Plant Nutrition. 34:1558-1566.
- Wagle, P., Smith, M.W., Wood, B.W., Rohla, C.T. 2011. Supplemental foliar nickel and copper applications do not reduce kernel necrosis in pecan trees receiving excess nitrogen. Communications in Soil Science and Plant Analysis. 42:2219-2228.
- Wood, B.W., Reilly, C.C., Bock, C.H., Hotchkiss, M.W. 2012. Suppression of pecan scab by nickel. HortScience. 47(4):503-508.
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Progress 10/01/10 to 09/30/11
Outputs
Progress Report Objectives (from AD-416) 1. Provide improved horticultural tools for stabilizing pecan nut yields in alternate bearing pecan trees and orchards. 2. Develop an improved approach for orchard management of fungal diseases attacking developing fruit, based on enhancement of the tree's natural disease resistance mechanisms. Approach (from AD-416) Objectives are achieved via research and development efforts to introduce to commercial pecan producers new horticultural tools to improve production efficiency of commercial enterprises. The approach focuses on alternate bearing and pecan scab disease via introduction of the following tools: a chemical-based thinning strategy for regulation of crop-load; regulation of flowering and alternate bearing via plant growth regulators; an improved �conceptual tool� for managing alternate bearing; reduction of chemical stresses by improved nutrient element management with emphasis on zinc; and induction of greater natural tree resistance to fungal disease pests (such as pecan scab) via improved tree nutrition and systemic acquired resistance inducers. The approach includes numerous lab, greenhouse, and field based studies, but with a great deal of emphasis on field evaluation of treatments in real-world commercial orchard situations. Extension specialists are included in the research efforts to facilitate transfer of knowledge, strategies, and technologies to farmers. The approach largely relies on adaptation of existing technologies to pecan horticulture, but with new technology potentially being introduced for transition and inner-transition metals, and registration of existing commercial products for usage on pecan. There will be dozens of research studies conducted, with experimental designs structured to test hypotheses associated with objective-linked postulates. Results will be disseminated to scientific, extension, and commercial individuals and groups via appropriate publications/articles, talks, and field-days. Chemical thinning: Excessive inconsistence in calcium hydroxide sprays to fruit-thin pecan trees means that an alternative approach merits pursuit. Additionally, it was determined that direct chemical thinning of fruit is unlikely to be efficacious for pecan due to the small number of fruit per fruiting cluster. The approach subsequent progressed to using gibberellic acid in �on� phase cropping years to reduce return bloom in the subsequent year�i.e., indirect thinning. Retention of fruit in the �off� phase year appeared feasible via timely usage of ReTain (an ethylene inhibitor) to prevent fruit abortion in June. Alternate bearing: Research validates that flowering and alternate bearing is regulated initially via balances involving plant growth regulators and then subsequently via carbohydrate reserves during vernalization; thus, leading to new approach using timely treatments with certain plant hormones to regulate subsequent year flowering. Zinc stress: Field studies in Georgia, Oklahoma, and New Mexico indicate that usage of zinc enriched implants to give long-term correction of zinc deficiency fails to sufficiently correct low zinc problems; thus, leading to consideration of a new approach involving banding with fine textured zinc enriched rubber as a slow release zinc form as a long-lasting solution. Additionally, special isotopically labeled zinc is being developed to enable determination of how foliar zinc is moving within trees; thus, potentially providing a better and cheaper means of controlling tree zinc nutrition. Scab disease: Field studies on the roles of nickel (Ni) and phosphite (PO3) for improving tree resistance to pecan scab disease found significant efficacy for both against scab disease; thus, leading to research integrating both into practical disease management strategies. The discovery of high concentrations of the rare-earth elements in foliage is suggestive that they play a biological role in disease resistance; thus, this possibility is being studied. Scab resistance: Several commercially available agents are in the process of being tested, on seedling trees under field conditions, for triggering pecan tree resistance to scab disease. Molecular biology based research is now enabling better understanding of critical life cycle traits and fungi variability characteristics that can potentially lead to improvement in disease management in orchards. Systemically acquired resistance to scab: Several commercially available agents are in the process of being tested, on seedling trees under field conditions, for triggering pecan tree resistance to scab disease. Scab resistance: Molecular biology based research is now enabling better understanding of critical life cycle traits and genetic variability of the scab pathogen that will contribute to improvements in disease management in orchards through optimal use of host resistance. Accomplishments 01 Regulation of flowering in pecan. The plant processes that regulate flowering in pecan has heretofore been a mystery, with the relative role of plant hormones and energy reserves being unknown. ARS researchers at Byron, GA, discovered that development of female flowers is initially regulated by an interplay of at least four classes of hormones within th bud meristem environment during the previous growing season, and subsequently regulated by non structural carbohydrate reserves within th same environment the following spring. This results in a new theory explaining how flowering in pecan involves a three-phase process acting during the twelve months preceding the visual expression of female flowe This identifies new research avenues for better understanding the specific physiological processes regulating flowering as well as enablin new opportunities for development of horticultural tools and strategies capable of on-farm regulation of flowering within pecan orchards. 02 A role for the micronutrient nickel to help reduce pecan scab in orchard Pecan scab can cause severe yield loss when environmental conditions ar conducive to epidemic development. Furthermore, resistance to certain fungicides used by pecan growers to control the disease demands an integrated approach to management of this disease. Field and in-vitro studies demonstrated a small but significant effect of foliarly applied nickel at reducing pecan scab. By optimizing nickel nutrition growers a better managing the pecan scab in orchards and are reducing associated crop loss. 03 Use of phosphite to manage pecan scab in orchards. Pecan scab can resul in premature fruit-drop or reduced kernel quality. Emergence of scab resistance to certain classes of fungicides commonly used by pecan growe to control the disease provides compelling reason to identify novel chemistries with minimal environmental impact to use as alternatives. Field studies have confirmed that phosphite is highly efficacious for controlling scab in pecan orchards, and they are now registered for use pecan. These are the first studies to demonstrate efficacy of phosphite on pecan scab; thus, as a consequence, phosphites are being substantiall used in commercial pecan orchards to control scab. 04 Increasing nut yield with ReTain. Excessive fruit-drop greatly reduces orchard profitability with certain varieties and in certain years. ARS researchers at Byron, GA, found that a commercialized natural growth regulator product, AVG (ReTain), reduces premature drop of �Desirable� fruit under field conditions; thus increasing yield in certain years. T research identifies ReTain as a useful horticultural tool for managing crop load on certain sensitive alternate bearing cultivars; thus, providing farmers with a new tool for managing fruit-drop and alternate bearing. 05 Regulation of Alternate Bearing in Pecan. Alternate bearing is a major biological problem in pecan production. ARS researchers at Byron, GA, discovered that certain commercially available plant growth regulators c be used to influence subsequent season flowering; thus, providing possib new tools for regulating alternate bearing and flowering in commercial pecan orchards. These finding enable pecan farmers to reduce over- cropping in heavy crop-load years and to increase cropping in otherwise low crop-load years. 06 Identification of rare earth elements as likely beneficial micronutrient in pecan. Insufficient understanding of the nutrient element requiremen of pecan trees limits productivity and disease resistance. ARS researchers at Byron, GA, found that pecan and other hickory species accumulate relatively high concentrations of the rare earth elements, wi the species possessing a duplicate set of chromosomes being especially high accumulators. These elements appear to enable species survival und relatively high stress conditions and appear to be beneficial, or perhap even essential, nutrient elements that have heretofore been ignored in orchard nutrient management. This information will lead to improved nutrient management of orchards and will likely contribute to reduced us of fungicides and greater water use efficiency. 07 Improving accuracy and precision of pecan scab assessment. Pecan scab causes severe disease on fruit and leaves. Having an accurate, precise, repeatable and reproducible method to assess scab reduces error and improves the quality of data for comparing treatments, and thus ultimate the results on which management decisions are based. Development of a standard area diagram set aides scab disease assessment on fruit, which reduces error and variability in disease assessments.
Impacts
(N/A)
Publications
- Wood, B.W. 2011. Influence of aminoethoxyvinylglycine (AVG) on yield and quality of nut crops from a commercial pecan orchard. HortScience. 46(4) :586-589.
- Wood, B.W. 2011. Influence of plant bioregulators on pecan flowering and implications for regulation of pistillate flower initiation. HortScience. 46(6):870-877.
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Progress 10/01/09 to 09/30/10
Outputs
Progress Report Objectives (from AD-416) 1. Provide improved horticultural tools for stabilizing pecan nut yields in alternate bearing pecan trees and orchards. 2. Develop an improved approach for orchard management of fungal diseases attacking developing fruit, based on enhancement of the tree's natural disease resistance mechanisms. Approach (from AD-416) Objectives are achieved via research and development efforts to introduce to commercial pecan producers new horticultural tools to improve production efficiency of commercial enterprises. The approach focuses on alternate bearing and pecan scab disease via introduction of the following tools: a chemical-based thinning strategy for regulation of crop-load; regulation of flowering and alternate bearing via plant growth regulators; an improved �conceptual tool� for managing alternate bearing; reduction of chemical stresses by improved nutrient element management with emphasis on zinc; and induction of greater natural tree resistance to fungal disease pests (such as pecan scab) via improved tree nutrition and systemic acquired resistance inducers. The approach includes numerous lab, greenhouse, and field based studies, but with a great deal of emphasis on field evaluation of treatments in real-world commercial orchard situations. Extension specialists are included in the research efforts to facilitate transfer of knowledge, strategies, and technologies to farmers. The approach largely relies on adaptation of existing technologies to pecan horticulture, but with new technology potentially being introduced for transition and inner-transition metals, and registration of existing commercial products for usage on pecan. There will be dozens of research studies conducted, with experimental designs structured to test hypotheses associated with objective-linked postulates. Results will be disseminated to scientific, extension, and commercial individuals and groups via appropriate publications/articles, talks, and field-days. Chemical thinning. CaOH tested under commercial orchard conditions inhibited ovule fertilization and exhibited efficacy; however, there was insufficient control over degree of thinning for the approach to be practical. Efficacy of treating canopy zones is still being assessed. Alternate bearing. A) Nut yield and flowering was found to highly correlate with the amount of sugar in spring xylem sap; thus, linking flowering and crop-set to high sugar reserves, and the last stages of floral initiation to carbohydrate reserves. Also, there was progress on identifying the linkage between �switching� of endogenous tree resources and crop-set. B) Floral initiation was found to be regulated at three levels, with level-two regulation being equilibrium amount four different phytohormones, and level-three regulation being carbohydrate reserves at time of vernalization; thus, establishing a new theory of flower initiation and alternate bearing in pecan. Zn stress. Field studies found that zinc-implants in tree trunks do not correct zinc deficiency. Work was initiated to better determine the nickel-iron interaction in trees. Scab disease. Field studies tested the role of transition and inner- transition elements for improving tree resistance to scab. Phosphite proved especially good for preventing scab, and commercial products are now being used on pecan to control the disease. Present efforts are now focusing on rare earth elements and phosphite. Scab resistance. Several agents are in the process of being tested on seedling trees for potential to trigger tree resistance to scab disease. Phosphite exhibited evidence of SAR related activity. Molecular biology based research is being implemented to better understand scab genetics so as to be better able to control orchard scab epidemics. Subordinate Project Reports. Non-funded cooperative agreement, �Preventing Early-Season Fruit Drop,� (CRIS-21220-011-05N): Fruit abortions due to K deficiency were found to be the cause of yield loss in orchards. It is now recommended that orchards of �Desirable� be managed at higher K levels. It was also found that excessive usage of glyphsate herbicides also contributed to fruit drop. Non-funded cooperative agreement, �Increasing Fruit Retention and Overcoming Leaf Scorch and Scab of Pecan Trees,� (CRIS 6606-21220-011-06N) : Timely treatment of canopies with AVG (Retain) was found to reduce fruit-drop in �Off� years, but not in �On� years. Usage of ReTain in commercial orchards is practical in �Off� years. Accomplishments 01 Increasing crop-load and yield with ReTain. Excessive crop loss due to fruit-drop can greatly reduce profitability of certain orchard operation A commercialized natural growth regulator product, AVG (ReTain), was fou to possess potential for reducing nut-drop of certain pecan cultivars; thus increasing yield in �Off� crop-load years. The research identifies ReTain as a potentially useful horticultural tool from managing crop loa on certain sensitive cultivars; thus, providing farmers with the means t improve nutmeat yield in �Off� bearing years. 02 Potassium deficiency can trigger excessive fruit-drop. The cause of unexplained severe fruit-drop in �Desirable� pecan in commercial orchard was found to be due to insufficient potassium (K) in young developing fruit. Soil banding of potash rapidly increased the K concentration of foliage and fruit, and prevented fruit drop. Managing Desirable foliage a K concentration of 1.5% of more prevents K-associated fruit aborting i June. This research identified a deficiency in the K management recommendations by extension services, and sets new guidelines for orcha K management as well as how to better improve K uptake from soils, and h to more efficiently apply K to orchard soils. 03 Reducing alternate bearing by using gibberellic acid to increase tree resistance to black pecan aphids. Enhanced alternate bearing, and subsequent reduced profitability, is greatly accentuated by stress facto triggering premature senescence of canopy foliage or of premature defoliation. It was found that treating canopies with Gibberellic Acid, naturally occurring plant product, prevents black pecan aphids from bein able to trigger senescence of foliage or damage to tree canopies; howeve the hormone can reduce return flowering if applied at the wrong time of the growing season or at an excessive concentration. Efforts are underw to optimize the approach for both aphid control and return flowering. Th approach keeps populations of black pecan aphids from building to damagi levels in orchards. The approach offers a novel tool for controlling alternate bearing inducing black pecan aphid populations by treating canopies with a natural product growth regulator. This new tool has potential for use on all crops affected by senescence inducing aphids. 04 Identification of phosphite as a highly effective agent for controlling pecan scab in orchards. Premature fruit-drop or reduced kernel quality are devastating consequences of pecan scab disease on developing fruit. Additionally, there is emergence of scab resistance to certain classes o fungicides used in orchards. Field study found that phosphite is highly efficacious for controlling scab in pecan orchards, although the mechani of action is not yet fully understood. Certain phosphite products registered for use on other crops are now registered for use on pecan an are increasingly being used in commercial orchards to control pecan frui scab. 05 Improving water use on pecan in the southwestern U.S. Optimization of water use is a major goal in southwestern pecan orchards. A soil temperature model was developed to predict the soil temperature where pecan roots grow; thus, providing a means for estimating impact on tree root health, and ultimately tree water use. The model potentially assis in efforts to further improve water use efficiency and minimization of tree stress in pecan orchards.
Impacts
(N/A)
Publications
- Wood, B.W., Lombardini, L., Heerema, R. 2009. Influence of aminoethoxyvinylglycine on pecan fruit drop and yield of pecan. HortScience. 44:1884-1889.
- Wood, B.W., Wells, L., Funderburke, F. 2010. Influence of elevating tree potassium on fruit-drop and yield of pecan. HortScience. 45:911-917.
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Progress 10/01/08 to 09/30/09
Outputs
Progress Report Objectives (from AD-416) 1. Provide improved horticultural tools for stabilizing pecan nut yields in alternate bearing pecan trees and orchards. 2. Develop an improved approach for orchard management of fungal diseases attacking developing fruit, based on enhancement of the tree's natural disease resistance mechanisms. Approach (from AD-416) Objectives are achieved via research and development efforts to introduce to commercial pecan producers new horticultural tools to improve production efficiency of commercial enterprises. The approach focuses on alternate bearing and pecan scab disease via introduction of the following tools: a chemical-based thinning strategy for regulation of crop-load; regulation of flowering and alternate bearing via plant growth regulators; an improved �conceptual tool� for managing alternate bearing; reduction of chemical stresses by improved nutrient element management with emphasis on zinc; and induction of greater natural tree resistance to fungal disease pests (such as pecan scab) via improved tree nutrition and systemic acquired resistance inducers. The approach includes numerous lab, greenhouse, and field based studies, but with a great deal of emphasis on field evaluation of treatments in real-world commercial orchard situations. Extension specialists are included in the research efforts to facilitate transfer of knowledge, strategies, and technologies to farmers. The approach largely relies on adaptation of existing technologies to pecan horticulture, but with new technology potentially being introduced for transition and inner-transition metals, and registration of existing commercial products for usage on pecan. There will be dozens of research studies conducted, with experimental designs structured to test hypotheses associated with objective-linked postulates. Results will be disseminated to scientific, extension, and commercial individuals and groups via appropriate publications/articles, talks, and field-days. Significant Activities that Support Special Target Populations Chemical thinning: The ability of timely sprays of agents was assessed as a thinner, with best concentrations determined. Spreader-stickers did not affect efficacy. Agents were tested for potential to prevent pollen germination. Alternate bearing: The relationship between chemical composition and morphological traits of �on� and �off� bearing trees was correleated with yield and flowering. The feasibility of controlling flowering via regulation of auxin transport was tested. Zn stress: Field studies were implemented in Georgia, Oklahoma, and New Mexico regarding the implantation of zinc-implants into tree trunks to correct zinc deficiency without needing to spray zinc to canopies. Scab disease: Field studies tested the role of several transition and inner-transition elements for improving tree resistance to scab disease. Nutrients and fungicides were tested for impact on an emerging problem with kernel quality. Scab resistance: Several commercially available agents were tested that have the potential for triggering tree resistance to scab disease. Certain ones exhibited potential for enhancing tree resistance to scab. Subordinate Project Reports: SCA 58-6606-5-246 with New Mexico State University: A simple irrigation scheduling calendar was developed. The extent and duration of gas phase soil oxygen depletion in response to flood irrigations, and comparison of galvanic and chemi-luminescent sensors for detecting soil air oxygen was tested. A dendrometer was developed. Field work continued on projects of regulated deficit irrigation and pecan orchard floor management practices and effects on water use and nitrogen uptake efficiency. The SCA was monitored via 1 site visit, 1 meeting, and several phone calls and e-mails. SCA 58-6606-6-175 with the University of Arizona: A multiple year study on development of orchard methods to correct tree zinc deficiency via soil application was continued. Several different Zn sources (organic and synthetic-chelated) were applied via soil banding or incorporation, with subsequent monitoring of tree canopy nutrition. SCA activity was monitored via 1 site visit, 1 meeting, and phone calls and e-mails. Non-funded cooperative agreement, "Preventing Early-Season Fruit Drop," (CRIS 6606-21220-009-05N): Studies found that banding of potassium is superior to broadcasting. It increases fruit-set and yield of �Desirable� pecan; thus, indicating that poor potassium (K) nutrition is potentially affecting fruit-set in commercial orchards. Activities were monitored via on-site visits. Non-funded cooperative agreement, "Increasing Fruit Retention and Overcoming Leaf Scorch and Scab of Pecan Trees� (CRIS 6606-21220-009-06N) : Results indicate that timely treatment of canopy with ReTain reduces fruit-drop and increase in yield without loss of kernel quality. Activities were monitored via on-site visits. Technology Transfer Number of Other Technology Transfer: 3
Impacts
(N/A)
Publications
- Wood, B.W. 2009. Mechanical hedge pruning of pecan in a relatively low- light environment. HortScience. 44(1):68-72.
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