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In northern temperate zones, peach trees are vulnerable to cold temperature injury in the fall, particularly as climate change prolongs warm weather in the fall and potentially delays the onset of cold acclimation. Four experiments evaluated how cold acclimation of flower buds and shoot phloem, cambium, and xylem is affected by exposure to varying temperatures in the fall. One-year-old peach shoots from trees grown in Maine, USA, were collected from October through November, exposed to 1, 3, or 6 days of low, high, and freezing temperatures, and subjected to stepwise controlled freezing to about −30 °C. Injury was visually quantified as oxidative browning of flower buds and shoot tissues. High temperature exposure, even of a single day, decreased cold tolerance of flower buds and shoot tissues until late November, when high temperatures only minimally decreased cold hardiness. In mid-November, increasing the duration of high temperature exposure from 1 to 3 days decreased cambium and phloem hardiness, but hardiness in flower buds was not further decreased by the longer duration of 3 days. By late November, hardiness in flower buds, cambium, and phloem was less responsive to high temperature, and was increased by prior exposure to 6 days of freezing. After high temperature, xylem lost hardiness to a small degree in mid-October and late November, but in mid-November this occurred in only one experiment. In this study, deacclimation during high temperature in the fall was greater in cambium and phloem than in flower buds and at times greater than in xylem.

Cold tolerance was measured midwinter in a New Hampshire, USA, orchard collection of 33 peach and nectarine cultivars over 3 years using natural and artificial freezing methods. Flower bud survival and xylem and cambium hardiness were based on the inflection point from nonlinear regression, as well as comparisons of injury at about −20 °C. Flower bud hardiness was greatest in ‘BuenOs’, ‘Contender’, ‘Cresthaven’, ‘Redhaven’, and ‘Scarlet Rose’. The lowest hardiness occurred in ‘Brigantine’, ‘Desiree’, ‘Emeraude’, ‘Evelynn’, ‘Galaxy’, ‘Glenglo’, ‘Jade’, ‘PF5D’, ‘PF23’, ‘Silverglo’, ‘Spring Snow’, and ‘Sugar May’. Other cultivars had either intermediate or inconsistent year-to-year bud hardiness. Bud hardiness in 2021 was weakly correlated with bud hardiness in 2023, but neither were correlated with bud mortality in 2022 after a severe freeze. Cambial hardiness in one year was not correlated with hardiness in other years. ‘August Rose’, ‘BuenOs’, ‘Cresthaven’, ‘Desiree’, and ‘Silverglo’ had the hardiest cambium which was consistent from year to year. Xylem hardiness was greatest in ‘BuenOs’, ‘Contender’, ‘Desiree’, ‘John Boy’, ‘PF17’, ‘Redhaven’, ‘Silvergem’, and ‘TangOs’. Xylem injury was significantly correlated across years indicating that this tissue responds more consistently to midwinter freezing temperatures than flower buds and cambium.

This review was conducted to synthesize current knowledge, learn producer and Extension specialist perspectives, and identify gaps in understanding of the role of soil health in sustaining production in high tunnel (HT) systems. This synthesis includes findings from scholarly resources related to soil health in HTs, including research and Extension-based literature, perspectives from experienced HT producers and technical assistance providers, and the direct observations of a broad network of university research and Extension personnel working with HTs. Findings are intended to identify knowledge gaps and additional research and Extension resource needs of greatest priority to the HT producer community and technical assistance providers that support them at the time of publication. A review of 68 research articles and 58 Extension resources was conducted. Focus group interviews were conducted with small groups of experienced HT farmers in four regions of the eastern half of the United States, with in-depth farm case studies conducted in individual farmers in three of these regions. Growers across regions identified soil fertility management, soilborne diseases, soil compaction, and lack of consistency of soil analyses specific to HTs as the greatest soil-related challenges to HT production. Research and resources for technical assistance providers on mitigation strategies to remediate yield-limiting HT soil conditions, such as excessive soil salinity and high pathogen populations, were also lacking. As such, process-based research on techniques such as leaching, soil steaming, solarization, and anaerobic soil disinfestation in tunnels that consider short- and long-term costs, benefits, and effects on soil and plant productivity should be prioritized in the future when considering the impact of HT production on soil health. Interviews also indicated a need for networking opportunities for technical assistance providers across agencies (e.g., Natural Resources Conservation Service, Extension, nongovernmental organizations). Despite a high and increasing rate of adoption, there is currently a lack of information about maintaining HT systems. Given that HTs play a critical and growing economic role for specialty crop growers throughout the eastern United States, comprehensive intervention across the research–Extension spectrum to sustain productivity in HT systems is recommended.