2011 Annual Report 4.Accomplishments 1. Regulation of flowering in pecan. The plant processes that regulate flowering in pecan has heretofore been a mystery, with the relative roles 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 the bud meristem environment during the previous growing season, and subsequently regulated by non structural carbohydrate reserves within that 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 flowers. This identifies new research avenues for better understanding the specific physiological processes regulating flowering as well as enabling new opportunities for development of horticultural tools and strategies capable of on-farm regulation of flowering within pecan orchards. 2. A role for the micronutrient nickel to help reduce pecan scab in orchards. Pecan scab can cause severe yield 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 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 are better managing the pecan scab in orchards and are reducing associated crop loss. 3. Use of phosphite to manage pecan scab in orchards. Pecan scab can result in premature fruit-drop or reduced kernel quality. Emergence of scab resistance to certain classes of fungicides commonly used by pecan growers 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 on pecan. These are the first studies to demonstrate efficacy of phosphite on pecan scab; thus, as a consequence, phosphites are being substantially used in commercial pecan orchards to control scab. 4. 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. The 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. 5. 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 can be used to influence subsequent season flowering; thus, providing possible 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. 6. Identification of rare earth elements as likely beneficial micronutrients in pecan. Insufficient understanding of the nutrient element requirements 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, with the species possessing a duplicate set of chromosomes being especially high accumulators. These elements appear to enable species survival under relatively high stress conditions and appear to be beneficial, or perhaps 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 use of fungicides and greater water use efficiency. 7. 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 ultimately 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. Review 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.