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United States Department of Agriculture

Agricultural Research Service

Research Project: PECAN CULTIVATION AND DISEASE MANAGEMENT
2010 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. 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.


4.Accomplishments
1. 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, AVG (ReTain), was found 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 load on certain sensitive cultivars; thus, providing farmers with the means to improve nutmeat yield in “Off” bearing years.

2. Potassium deficiency can trigger excessive fruit-drop. The cause of unexplained severe fruit-drop in ‘Desirable’ pecan in commercial orchards 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 at a K concentration of 1.5% of more prevents K-associated fruit aborting in June. This research identified a deficiency in the K management recommendations by extension services, and sets new guidelines for orchard K management as well as how to better improve K uptake from soils, and how to more efficiently apply K to orchard soils.

3. 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; however, the hormone can reduce return flowering if applied at the wrong time of the growing season or at an excessive concentration. Efforts are underway to optimize the approach for both aphid control and return flowering. The approach 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.

4. 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 of fungicides used in orchards. Field study found that phosphite is highly efficacious for controlling scab in pecan orchards, although the mechanism of action is not yet fully understood. Certain phosphite products registered for use on other crops are now registered for use on pecan and are increasingly being used in commercial orchards to control pecan fruit scab.

5. 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 assists in efforts to further improve water use efficiency and minimization of tree stress in pecan orchards.


Review 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.

Last Modified: 11/26/2014
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