ASHS 2025 Conference

Phosphorus (P) is an essential plant nutrient required for growth. However, it is a finite natural resource that can cause environmental issues when overused in agriculture. Due to challenging soil relationships, the availability and uptake of P can be challenging to predict. Furthermore, soil tests can be misleading for guiding management decisions regarding P fertilizer applications. The objective of this study was to evaluate the influence of soil P levels on the uptake and partitioning of P in young peach trees. We planted a new peach orchard at the Musser Fruit Research Center near Clemson, SC. This orchard contained a widely variable range of P in the soil. Representative trees were removed in August and January and all plant parts were subjected to P analysis. Soil test P levels had no clear relationship with total plant P uptake or partitioning patterns and are likely a poor reference point for P fertilizer management decisions in peach orchards.

Nutrient leaching remains a significant environmental concern due to its adverse effects on soil quality, groundwater contamination, human health, and the eutrophication of aquatic ecosystems. The urgency of addressing this issue has escalated with the increasing frequency and intensity of climate variability and extreme weather events, which exacerbate nutrient losses from agricultural systems. For this study, three peach cultivars (Prunus persica L.), including 'Crimson Joy', 'Liberty Joy', and 'Rich Joy', were planted at Auburn University's Research and Extension Center in Chilton, Clanton, Alabama, on February 23, 2024, using a Randomized Complete Block Design (RCBD) with four blocks. Each block consists of 9 peach trees, totaling 36 trees. The aim of this study is to evaluate the extent of nutrient leaching on the growth of three distinct young peach cultivars, using recommended fertilization rate (by The Southeastern peach guide). A soil sampling method is used to compare the nutrient levels at selected depths. The soil depths are 25.4 and 50.8 cm within and 76.2 and 101.6 cm below the peach tree root zone. The collected soil samples are analyzed for Nitrate Nitrogen (NO3-N (mg/kg)), Ammonium nitrogen (NH4-N (mg/kg)) and pH. Additionally, the young peach trees are assessed by measuring plant height (cm), trunk cross-sectional area (cm2) and annual leaf nitrogen analysis (%). The preliminary results of this study, which is still in progress indicate that both depth and cultivar significantly influence NH4-N concentrations over time, while rainfall events and cultivar interactions affect NO3-N leaching dynamics. Although pH levels changed, they did not differ statistically. Each cultivar exhibited TCSA increases and height growth, with all cultivars maintaining leaf nitrogen levels within the optimum range. This study will help the Alabama peach growers to understand the impacts of nutrient leaching and utilize better alternatives that can help to not only get maximum profit economically but also ensure that the environment is safe and sound for the current and future generations.

Development of control measures for nutrient-related apple fruit disorders like bitter pit requires a better understanding of calcium metabolism in the tree. Limiting this understanding is a rapid and accurate method for measuring the concentration of calcium in various plant organs including the leaves. Optimally, measuring calcium levels could be done at the single leaf level, or better yet for whole leaves at a resolution of sub-millimeter dimensions. We report on the use of X-ray fluorescence for apple leaf tissue to quantitatively measure leaf calcium tissue. Using 7-mm diameter discs taken from Granny Smith apple leaves mid-season, we were able to demonstrate that the emission data from a scanning Bruker X-ray fluorescence instrument could be easily transformed to predict accurate and precise calcium levels in apple leaf tissue. If similar relationships can be determined for other minerals, this type of analysis will enable the quantitation of multiple minerals within minutes. Provided software analysis of the samples can be automated, the turn-around time for tissue analysis would be on the order of one or two hours for hundreds of samples

Plant nutrient acquisition and responses to different fertilization programs in fruit orchards oftentimes depend on many biotic or abiotic factors or a combination of both, including tree or orchard age and nutrient source. This study aims to evaluate the effect of topically applied, slow-release source of essential nutrients from mulch mixed with poultry litter (PLM) or without (M) and fast-release growers’ standard rate of mineral fertilizer on an eight-year-old replanted orchard containing ‘Juneprince’ and ‘Scarletprince’ peach trees in South Carolina. Soil health indicators such as soil moisture and nutritional status, and tree health parameters, including yield and fruit quality (specifically on the incidence of diseases and physiological disorders), were evaluated over two years. The results showed that soil organic matter and cation exchange capacity were significantly higher in PLM across both years of this study when compared with other treatments. Both PLM and M treatments had higher moisture retention than the grower’s standard. However, yields between the two cultivars used in this study varied considerably in response to treatment and years. Yield of ‘Juneprince’ trees treated with GS was significantly higher in the first year of this study when compared with PLM and M but did not significantly differ in the second year. In contrast, yield of ‘Scarletprince’ trees treated with PLM and M were consistently higher numerically when compared with GS in both years. PLM significantly reduced bacterial spot incidence and severity in both cultivars across the study years. This result suggested that amending the soil through surface covering with mulch mixed with poultry litter provides the nutritional requirement, increases yield and significantly lower disease pressure and improves the quality of the marketable fruit in a mature orchard.

Southwest Native American Tribes, such as the Navajo, Hopi, and other Pueblo, have grown peaches since at least the early 1600’s, making them a nutritionally and culturally important food source. Historically, peach propagation was primarily done by seed, with only one written account of stem cutting propagation occurring within the Zuni Pueblo. Little is known about the effectiveness of different propagation methods for rapidly replicating Southwest seedling accessions and maintaining parent tree genetics. The purpose of this study was to evaluate the rooting success of softwood and hardwood cuttings taken from Southwest peach seedling accessions originating from five locations within the Navajo and Hopi Tribal communities. All cuttings were collected from mature trees established in Thatcher, UT. Two trials of cuttings were conducted in July and November of 2024. Each seedling tree had 18 cuttings per trial. Trial one had softwood and hardwood cuttings and trial two had only hardwood cuttings. Each cutting was measured 12 cm long, had at least three nodes planted into the potting media. Trial one cuttings had the first 3 node leaves cut in half, with all other leaves removed. Cutting treatments included a control (no treatment), Hormodin 1, and Hormodin 2, with six replications for each treatment. All cuttings were placed under a mist system with controlled temperature and relative humidity. Rooting success was assessed over three months by visually evaluating live tissue and new growth. Rooting success was dependent upon seedling parent location, treatment, time of year, as analyzed by analysis of variance. Cuttings from Canyon del Muerto had greater rooting success compared with those from Navajo Mountain. The Hopi and Navajo Mountain cuttings had decreased rooting success as the Hormodin concentrations increased. Canyon del Muerto cuttings benefited from Hormodin 1 treatment. The results of this study will help determine the potential of Southwest peach seedlings for replication as a viable rootstock for the fruit industry.

Plant canopy and root architecture characteristics play a crucial role in water uptake and plant growth. Blueberry roots are shallow and lack dense root hairs, making them more susceptible to drought than most fruit crop species. In northern highbush blueberry (Vaccinium corymbosum), differences in root size, root architecture, and root-to-leaf balance may impact drought resilience, particularly in maintaining photosynthesis (A) under limited soil moisture. However, this has not yet been examined in this species. This study evaluated drought resilience in two V. corymbosum genotypes with contrasting canopy and root architecture characteristics (Bluecrop, low root-to-leaf ratio; Draper, high root-to-leaf ratio). During the pre-drying period, both genotypes exhibited similar A and stem water potential (Ψ stem). Irrigation water was withheld to initiate drought conditions. By day 4 of withholding water, Bluecrop showed a decline in A, but its Ψ stem did not significantly change until day 6. In contrast, Draper did not show a decline in A or Ψ stem until day 6 of withholding water. Both cultivars reached a critical threshold of stomatal conductance (gs) (90% reduction from well-watered conditions) on day 10 of withholding water. Following re-watering, Ψ stem recovered immediately in both cultivars on day 2 of re-watering (day 12 of withholding water). However, the recovered Ψ stem of Bluecrop did not correspond with any increase in gs until day 14 of rewatering (day 24 of withholding water). Meanwhile, Draper exhibited a much higher gs and A than Bluecrop throughout the post-rewatering period, suggesting that Bluecrop is more sensitive to drought conditions than Draper. Post-experiment analysis confirmed that Draper had a larger root-to-leaf ratio than Bluecrop, which likely enhanced water absorption and supported faster recovery following rehydration. No significant difference in root architecture characteristics were found between these two cultivars, considering the number of root tips, root length, and surface area per root diameter at different levels (< 0.25 mm, 0.25- 0.5 mm, and >0.5 mm). These results suggest that root-to-leaf ratio and root-to-leaf hydraulic conductance play a central role in determining drought resilience in V. corymbosum genotypes. Future studies will be carried out to confirm this finding across a greater number of genotypes.

Consistent production (CP) of quality crops supports economic sustainability of individual farms and maintains market share for a larger industry. For the last 30 years, annual prune production in California has been highly variable, ranging from < 1 to >3 dried tons per acre. ‘Improved French’ is the primary cultivar grown in California. This variety, like most plums, often requires thinning to maintain CP and grower income where fruit size (count per pound) is positively correlated to fruit quality and price to the grower. Mechanical shaking at reference date, ~45 days after full bloom, is now a common thinning practice although questions have been raised regarding the potential benefit to earlier thinning a phantom practice that would have to be chemical thinning. However, in the last two decades, extreme bloom weather can virtually eliminate a prune crop if warm weather precedes bloom. This talk reviews work by University of California researchers towards improving CP through 1) better understanding of the weather related factors contributing to very low fruit set in prunes, 2) testing ‘Improved French’ prune fruit growth development to determine if and when source limited fruit growth occurs, and 3) identifying chemical thinning practices, materials, and rates to remove flowers before fruit set. Early bloom years are those with risk of crop loss due to extended and wet or extremely warm (>27oC) bloom weather conditions. [The risk of freezing damage is relatively low for prunes in CA given usual March bloom timing.] Relative prune fruit growth rate studies revealed resource limited fruit growth occurs ahead of current thinning timings (reference date), so earlier thinning may improve fruit growth and possibly yield compared to the current thinning practice. Finally, potassium thiosulfate (KTS) applied 2x at 1-2% (v/v) shows promise in thinning prunes. Lime sulfur and fish oil can be effective but is inconsistent in bloom thinning. Obstacles to CP of ‘Improved French’ prune include difficulty identifying practices to quantify bloom strength and help grower with the decision to thin or not. In addition, no ‘rescue’ spray has been found to improve fruit set in years with early, risky, bloom. Grower testing of the current research results awaits successful overcoming of the two obstacles listed above.

Precision crop load management is important for increasing yield, fruit size, and quality of apple production, particularly for the ‘Honeycrisp’ variety, which is highly susceptible to biennial bearing and difficult to thin. The MaluSim model, developed at Cornell University, can be used to guide crop load management by modeling carbohydrate balance to optimize fruitlet thinning. However, this model was developed using tree performance in New York and may not account for higher temperatures in Washington State, which may affect canopy growth and development. The objective of this study was to assess early season canopy growth and evaluate carbon partitioning of Honeycrisp apples grown in Washington state climatic conditions. The first experiment compared the canopy growth of Honeycrisp topworked in 2016 onto a ‘Granny Smith’ planting with M.9T337 as a rootstock. The topworked trees were trained to single, double, or triple-axis trees. The second experiment assessed carbon partitioning of Honeycrisp trees conducted under single, double, and triple leader(s) training systems. Training systems significantly impacted shoot length and the number of shoots. Single-axis trees had significantly longer shoot lengths and higher shoot numbers than the double and triple-axis training systems. Canopy imaging was also used to assess canopy infill and light interception. The second experiment weighed the biomass partitioning of the various tree parts (spurs, 1-year growth, leaves, branches, roots, rootstock, inter-stem, and fruits). Below-ground portions of all training systems accounted for more biomass than above-ground portions. There was smaller wood and a greater proportion of spur buds in the double and triple-axis trees compared to single-axis trees. The differences in carbon partitioning and canopy development among different training systems compared to the types of trees used when developing the MaluSim model may affect how the MaluSim model performs.

Multiple digital imaging companies can gather apple orchard data to map flower bud load, flower cluster number and fruitlet number at the tree level. However quickly matching photographic survey data to maps which can accurately guide management decisions remains challenging. Over the past year, Cornell University has partnered with several companies which can collect and apply survey data to guide precision pruning, precision blossom thinning, and precision fruitlet thinning in high density apple orchards of Western New York. Photographs and surveys from companies which collect single tree information provided the highest resolution information to guide precision sprayers. Precision sprayers were able to successfully apply treatments to the tree level, but the survey data first needed to be transformed into task maps which defined unique tree positions using the same GPS system used to collect the data and then control the sprayer to avoid an offset. Improving orchard management using digital tools may help improve crop load management but the success of this effort depends on the treatment resolution (section of row vs individual tree) as well as when crop load was modified, such as pruning, blossom, and or fruitlet timing.

Fruit growth across various stages of development determines the extent of final fruit size, and is therefore of high economic value. The two main processes that mediate growth, cell production and cell expansion, contribute differentially to growth across various stages of fruit development. In apple, growth during early fruit development is largely facilitated by cell production. Mid and late stages of fruit development display growth mediated mostly by cell expansion. Mechanisms that regulate these processes and consequently the growth rates of fruit are not well understood. The objective of this study was to determine the molecular processes associated with higher relative growth rates (RGR) in the apple fruit during different stages of development. To address this objective, we exploited the inherent natural variation in RGR within a population of ‘Empire’ fruit. These evaluations were performed during early and mid-fruit development stages. At each stage, change in fruit size (volume) was determined across a 4 d interval to obtain the RGR. The population of fruit was grouped into two classes based on their RGR values: High and Low RGR. RNA-sequencing analyses were performed to compare the transcriptomes of the two classes of fruit. During early fruit development, the High RGR class fruit displayed 1.46-fold greater growth rates than the Low RGR fruit. Transcriptome analysis indicated that genes associated with cell division processes such as HISTONES, CYCLINS and CYCLIN DEPENDENT KINASES were more abundant in fruit with higher RGR. During mid-fruit development, fruit displayed relatively lower RGR. Yet the High and Low RGR fruit classes differed by 1.76-fold. However, only a limited set of genes, mostly associated with oxidation-reduction processes, were differentially expressed across these two groups. Overall, these data suggest that processes that regulate cell division control the growth rates of apple fruit during early fruit development.

Thinning remains a critical yet challenging practice in apple production, especially for organic systems where chemical tools are limited. Since 2017, our research has evaluated the use of insect-exclusion netting as a sustainable, non-chemical strategy to simultaneously manage crop load and reduce pest pressure. What began as small-scale trials has expanded to commercial-scale implementation in Michigan, supported by USDA funding. Over the course of eight years, we evaluated netting on a diverse suite of cultivars including 'Gala', 'Fuji', 'SweeTango’, Liberty’ and 'Honeycrisp' in multiple locations. Canopies were enclosed at varying bloom stages, and results consistently demonstrated that netting significantly reduced fruit set in proportion to the amount of open bloom at the time of application. Cultivar-specific responses were observed: Gala’ and 'Fuji' achieved optimal crop loads when netted between 25% and 50% bloom, while ‘SweeTango’ and 'Honeycrisp' often required higher percentage of open bloom. In several trials, netted trees yielded commercial fruit numbers without requiring hand or chemical thinning. Fruit size and quality remained similar to conventional treatments, while seed content was reduced without negatively impacting fruit development. In many cases, trees netted at the ‘pink’ phenology stage produced adequate fruit set of low seed-content fruit despite the exclusion of pollinators. Importantly, molecular genotyping using 16 SNP markers revealed that seed parentage in netted canopies overlapped with known pollinizer genotypes. This ruled out self-pollination and suggested that wind, rather than insects, facilitated cross-pollination under netted conditions. Additionally, fruit retention was linked to seed content at the population level, not the individual fruit level, further supporting the viability of non-insect pollination under netting. In 2024, we implemented nets in commercial orchards in Michigan to validate scalability. Netting treatments at 30% and 60% King Bloom produced yields and fruit quality metrics comparable to conventional thinning. Pest monitoring confirmed male codling moth exclusion and reduced San Jose scale captures, though woolly apple aphid and flower thrips populations increased under nets given the exclusion of natural predators Collectively, our results indicate that exclusion netting is a promising, multifunctional tool for organic and sustainable apple production. Beyond thinning and pest control, netting systems enable effective crop set through wind-mediated pollination, challenging traditional assumptions of insect dependency. Adoption of this system may require revised orchard design to optimize pollen flow, but offers significant environmental benefits, including reduced chemical inputs, support for pollinator conservation, and improved climate resilience in Midwestern apple orchards.

Heat or drought stress during critical stages of bud differentiation can result in the formation of double pistils in many stone fruits. If these flowers are pollinated, the resulting malformed “double” or “twin” fruit are not marketable. The frequency of double fruit in Utah tart cherry orchards has increased in recent years. To determine the critical time of flower bud formation for doubling, whole-tree treatments of induced heat stress were imposed for one-week intervals from July to September in 2022 and 2023. The resulting doubling incidence was observed in the following spring and at harvest. There were seasonal differences in the frequency of doubled fruit between years, but the highest incidence of doubling in both years resulted from induced heat stress at 4 to 6 weeks after harvest. Understanding this timing is important in targeting alleviation strategies such as evaporative cooling or spray-on orchard protectants.

Pawpaw (Asimina triloba) is a temperate, deciduous fruit tree native to North America and a member of the custard apple family (Annonaceae). It produces unique, flavorful fruit with a taste resembling mango, banana, and pineapple, making it valuable for various value-added products such as jams, bread, ice cream, and brandy. Pawpaw fruits are also rich in nutrients, vitamins, and antioxidants, contributing to their increasing commercial potential. However, fruit sets in some cultivars may be limited due to the protogynous and self-incompatible nature of pawpaw flowers, which require external pollinators for successful fertilization. Unlike many fruit-bearing species, pawpaw has been thought to be pollinated by beetles and flies rather than bees. However, their abundance and role in pollination remain understudied. This study aims to identify and quantify insect visitors to flowering and non-flowering branches of two pawpaw cultivars, ‘Sunflower’ and ‘Susquehanna’. Ten trees of each cultivar were selected, and a completely randomized design was implemented setting up 20 wire cage traps coated with tangle-trap adhesive (The ORTHO Group, Marysville, OH 43040) on flowering and 20 on non-flowering branches. After an 18-day flowering period, the traps were collected, and captured insects were identified to the level of order and their abundance recorded. In 2024, 20 traps were placed at control sites outside the orchard (roadsides and fields), and nine days of direct observations were conducted to document insect activity on male and female flower stages. Data were analyzed using RStudio v.2023.09.1 (Posit, PBC, Boston, MA) and subjected to an ANOVA, with flowers, cultivars, and years as treatment factors, followed by Least Significant Difference (LSD) means separation. Results from 2023 indicate a significantly higher abundance (p-value< 0.0001***) of Coleopteran insects on both flowering and non-flowering branches of ‘Sunflower’ and ‘Susquehanna’ compared to 2024. In 2023 Coleoptera was significantly higher in the flowering branch (p-value 0.0255*) and had an interaction of cultivar and flowers (p-value 0.04767*) while in 2024 Diptera was substantially higher in the non-flowering branches (p-value 0.04009 *) This study provides valuable insights into the pollination ecology of pawpaw, aiding in the development of strategies to enhance fruit set and improve commercial production as the species transitions into broader commercialization.