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United States Department of Agriculture

Agricultural Research Service

Related Topics


Location: Fruit and Nut Research

2009 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: 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.

4. Accomplishments
1. Establishment of Mechanized Hedge Pruning as a Light Management Tool Suitable for the Southeastern U.S.: Orchard crowding, with an associated loss of nutmeat yield and increase in alternate bearing, is a major problem for many pecan farmers. Several mechanized hedge pruning strategies were tested in the relatively low sunlight southeastern U.S. for their ability to increase light, fruiting, and yield. Results support the notion that hedge pruning can work in low sunlight regions, if done properly. The work supports the use of mechanized hedge pruning in the southeastern U.S. as a viable light and canopy management tool.

2. Increasing Crop-load and Yield with ReTain: Excessive crop loss due to fruit-drop can greatly reduce profitability of certain orchard operations. A commercialized natural growth regulator product (ReTain) was determined to possess potential for reducing nut-drop of certain pecan cultivars; thus increasing yield. The research identifies ReTain as a useful horticultural tool from managing crop load on certain sensitive cultivars; thus, providing farmers with the means to avoid excessive fruit-drop.

3. Nickel Deficiency can be Caused by Excessive Zinc and/or Copper: The cause of increases in the incidence and severity of nickel deficiency in certain crops is uncertain. Greenhouse and field studies found that nickel deficiency can be triggered by excessive zinc and/or copper in plant tissues; thus, reducing the biological availability of nickel to plant growth processes. This identifies factors that can explain the occurrence of nickel deficiency in agriculture and provides insight into how to manage crop systems to avoid nickel deficiency and increase the sustainability of American agriculture.

4. 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 factors triggering premature senescence of canopy foliage or of premature defoliation. It was found that treating canopies with Gibberellic Acid, a naturally occurring plant product, prevents black pecan aphids from being able to trigger senescence of foliage or damage to tree canopies. The approach also keeps populations of black pecan aphids from building to damaging 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.

5. Identification of the Cause of the Spring Shoot Dieback Malady: Death of young shoots during early spring can reduce nut yield from commercial pecan operations. The cause of the problem has traditionally been attributed to cold injury; however, damage often occurs in absence of cold temperatures. Affected tissues was evaluated for presence of pathogens that might be causing the problem. It was found that the problem is probably due to shoots being infected with Phomopsis sp., a fungus harmful to pecan. Identifying the cause of the problem subsequently allows for development of control measures that will reduce crop loss due to the Spring Shoot Dieback disease.

6. Improving Water Use on Pecan in the Southwestern U.S.: There was development of a Simple Irrigation Scheduling Calendar for Mesilla Valley Pecan Growers. There was also an assessment of the extent and duration of gas phase soil oxygen depletion in response to flood irrigations in two pecan orchards. There was comparison of galvanic and chemi-luminescent sensors for detecting soil air oxygen in flood-irrigated pecans. A type of band and point dendrometer for measuring stem diameter growth was developed.

Review Publications
Wood, B.W. 2009. Mechanical hedge pruning of pecan in a relatively low-light environment. HortScience. 44(1):68-72.

Last Modified: 06/26/2017
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