Location: Fruit and Nut Research2012 Annual Report
1a. 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.
1b. 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.
3. Progress Report:
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.
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.