Kerik D. Cox

Fire blight is a destructive disease of apple and pear, and its severity is intensified under humid conditions. Biological controls are important components of the integrated management of plant diseases; however, field trials in the eastern United States have shown that currently available bacteria- and bacteriophage-based biocontrols lack the consistency and efficacy needed to meet industry standards under humid conditions. Blossom Protect is a yeast-based biocontrol agent developed for fire blight and postharvest diseases of apple. Although Blossom Protect has shown effectiveness in the Pacific Northwest under arid conditions, its efficacy has not yet been tested at a large scale in the eastern United States. In this study, we conducted a multilocation, multiseason field evaluation of Blossom Protect to determine its effectiveness in suppressing fire blight. Blossom Protect consistently suppressed blossom blight incidence, with an average disease suppression determined at 63.9%, which exceeded that of oxytetracycline (57.1%) but remained lower than that of streptomycin (79.3%). The disease suppression efficacy of Blossom Protect was further enhanced by the use of a contact sterilant, Oxidate, in an integrated management program. Blossom Protect increased fruit russeting; however, russeting was limited to 6 to 10% of the fruit surface on average and did not increase the proportion of out-of-grade fruit. We also assessed compatibility with fungicides commonly applied during bloom and found Blossom Protect to be incompatible with conventional multisite and quinone outside inhibitor (FRAC M and FRAC11) fungicides, as well as OMRI-listed contact sterilants and sulfur-based materials.

Pseudoperonospora cannabina, the causal agent of downy mildew in Cannabis sativa, was first identified in New York in 2020. The pathogen causes angular brown lesions on foliar tissue and dark sporulation on the leaf underside, often leading to leaf curling, defoliation, and yield loss. To date, no sources of genetic resistance or effective chemical controls have been reported. In this study, 108 hemp entries were evaluated for resistance to downy mildew using three phenotyping methods: 1) high-throughput Blackbird robotic imaging coupled with convolutional neural network-based leaf disc analysis, 2) visual rating of the same leaf discs, and 3) detached leaf assays. Susceptibility ranged from 0 to 100%, with two entries, G 33532 and ‘Santhica 27’, exhibiting 0% severity across all three phenotyping methods. Detached leaf assays produced the lowest disease severity estimates, whereas Blackbird convolutional neural network ratings exhibited the lowest residual variance but consistently underestimated disease severity relative to visual assessments. Visual leaf disc ratings produced the highest severity estimates and had the greatest variability. These results suggest that while Blackbird convolutional neural network analysis holds promise for high-throughput phenotyping of the hemp downy mildew interaction, additional refinement is required to improve accuracy.

Apple scab, caused by Venturia inaequalis, requires regular fungicide applications to achieve adequate disease control. Multi-site fungicides such as mancozeb and captan are integral to chemical management programs due to resistance concerns. To reduce this reliance on multi-site fungicides and mitigate regulatory concerns, there has been increased demand for more sustainable solutions. We attempted to integrate biopesticides into management programs with single-site fungicides using disease forecasting to better time applications. Disease incidence on terminal leaves and fruit was rated at the end of the season; mean incidence was calculated and analyzed. No significant differences (P > 0.05) were observed among management programs suggesting that integrated programs would be viable and that forecasting-based timing can be just as effective as a calendar schedule. While the results seem promising, we can’t be certain whether the multi-sites fungicides or biopesticides were effective rotational or simply not needed without additional controls. Regardless, growers will want to apply something for fungicide resistance management and to maintain a modicum of coverage and during low-risk infection periods. Of the options, biopesticides are one of the more environmentally responsible. Compared to the vertical axis planting, the super spindle planting had lower canopy relative humidity and fewer days where the relative humidity exceeded 90%. While we observed lower incidence of disease in the super spindle planting in years 2022 and 2023, this was not the case in 2024. Hence, the potential for successfully using biopesticides for apple scab may not be more easily accomplished by super-spindle plantings. Given that we observed no significant differences (P > 0.5) in the incidence of apple scab symptoms of leaves and fruit between integrated and conventional programs during this two-year study, it may be possible to achieve adequate disease control without the use of synthetic multi-site fungicides when single-site fungicides are used optimally in rotation biopesticides.

Apple scab, caused by Venturia inaequalis, requires regular fungicide applications to achieve adequate disease control. Multi-site fungicides such as mancozeb and captan are integral to chemical management programs due to resistance concerns. To reduce reliance and mitigate regulatory concerns with multi-site fungicides, there has been increased demand for more sustainable solutions. We attempted to use disease forecasting to enhance potential for alternative programs replacing multi-site fungicides with biopesticides to manage apple scab in plantings of cvs. Jonagold and Empire apples. Programs included: untreated control, ‘grower-standard’ program of conventional multi-site fungicides alternated with single-site fungicides on a calendar schedule, a program where biopesticides alternated (in place of multi-sites) with single-sites on calendar schedule, several programs where biopesticide alternated (in place of multi-sites) with single-sites timed using one of three different disease forecasting tools (NEWA, RIMpro, or Weather services). Programs were carried out for standard and extended season management trials. Disease incidence on terminal leaves and fruit was rated at the end of the season; mean incidence was calculated and analyzed. In all years of the study on ‘Jonagold’ apples, we observed no significant differences (P > 0.05) among management programs suggesting that integrated programs would be viable and that any forecasting-based timing used in our study can be just as effective as a calendar schedule. For the cv. ‘Empire’ apples, which are more susceptible to apple scab, the extended season program with NEWA based applications provided the best control. Despite the promising results using biopesticides instead of multi-site fungicides, we can’t be certain whether the multi-sites fungicides or biopesticides were effective rotational partners are simply not needed without additional studies without additional controls. Regardless, something is needed to provide a modicum of coverage and ensure fungicide resistance management during low-risk periods, and biopesticides are one of the more environmentally responsible means. However, our results provide a cultivar dependent framework for developing management programs without multi-site fungicides using disease forecasting, while achieving better disease control and ensuring fresh market yields.

Bacteriophages are viruses capable of infecting bacterial cells. Lytic phages, which infect and kill bacterial cells, are of interest in disease management in human, animal, and plant systems. In plant pathology, the biocontrol of bacterial diseases is of heightened interest because of the lack of efficacious options in many pathosystems. Numerous papers have been published in the past few decades on phage that target plant pathogenic bacteria, and a large majority of these have been focused on phage isolation and characteristics that highlight the promise and potential of phage as biocontrol agents. In contrast, relatively few of these papers have reported results from studies conducted in the field. Of the recent papers (2022 to 2025) reporting field studies, disease efficacy results are inconsistent. We argue that field studies should be an essential component of phage biocontrol research to understand how to best utilize and deploy phages to generate consistently effective disease management.

Fire blight, caused by the bacterium Erwinia amylovora, is a major problem for apple and pear growers. Antibiotics (streptomycin and kasugamycin) are commonly applied during apple blossom in spring to control fire blight. Various alternative strategies for controlling fire blight have been attempted, but they are often less effective and sometimes more costly than antibiotic treatments. Although the catalyzation products of water by nanoparticles (NPs) of the mineral titanium dioxide (TiO₂) and UV radiation have been shown to be a highly effective bactericide, they have not been demonstrated to control fire blight. We conducted field studies at a research orchard in central New York and a commercial orchard in eastern New York. We found that applying low concentrations (450 to 1,300 ppm) of TiO₂ NPs combined with natural solar radiation controlled fire blight as effectively as streptomycin, both at the research orchard and at the commercial orchard. TiO₂ NPs are priced comparably to streptomycin, suggesting that TiO₂ NP photocatalysis may be a cost-effective strategy for controlling fire blight. [ ] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Glomerella leaf spot (GLS) and bitter rot caused by species in the Colletotrichum gloeosporioides species complex are the most economically devastating fungal diseases of apples in North Carolina. Crop losses have reached 100% in highly susceptible cultivars. In the southeastern United States, management of this disease has predominantly relied on broad-spectrum fungicide programs targeting several summer diseases of apples. To improve control of GLS and bitter rot, field experiments to evaluate the efficacy of multi- and single-site fungicides were conducted over multiple years in a ‘Gala’ research orchard in Mills River, NC, from 2017 to 2019. Fungicides representing different modes of action were applied in a nonrotational program from petal fall until the immediate preharvest period to assess their efficacy in reducing GLS incidence, shoot defoliation caused by GLS, and pre- and postharvest bitter rot. Of the fungicides evaluated, Captan 80WDG (active ingredient [a.i.] captan), Merivon (a.i. fluxapyroxad and pyraclostrobin), Cabrio (a.i. pyraclostrobin), and Aprovia (a.i. benzovindiflupyr) provided good to excellent control against disease caused by Colletotrichum chrysophilum. In these programs, the incidence of GLS, expressed as the relative area under the disease progress curve, ranged from 4.6 to 43.8 in the Captan 80WDG (2019) and the Aprovia (2017) programs, respectively. The incidence of bitter rot at harvest in these programs from 2017 to 2019 ranged from 0.0 to 45.3% in the 2018 and 2017 Captan 80WDG programs, respectively. Conversely, the highest incidences of GLS and preharvest bitter rot were consistently observed in the Inspire (a.i. difenoconazole), Sercadis (a.i. fluxapyroxad), and untreated programs. Shoot defoliation owing to GLS followed a similar trend across the evaluated fungicide programs. In addition to nonrotational fungicide programs, the effect of carrier water pH for applications of captan was evaluated for bitter rot control in Virginia and North Carolina. No differences in captan efficacy were observed at either location. The results of this study will inform the development of new management programs for GLS and bitter rot in the southeastern United States and provide a foundation for the development of new season-long fungicide programs for apple disease management.

Fire blight is an economically devastating disease caused by the bacterium Erwinia amylovora. Blossom infections can lead to shoot blight and, when unmanaged, become systemic and can quickly cause tree death and spread through an orchard via active infections sites producing bacterial ooze. With climate change, increasingly popular high-density training systems, and the susceptibility of many consumers’ desired apple cultivars, shoot blight management has become exceptionally challenging despite the diverse management tactics available. To better understand pruning as a management practice, we evaluated 10 pruning programs in two different orchards over the course of 2 years. The pruning programs in this study encompass extension recommendations and grower preferences and include a variety of supplemental chemical applications and sanitation practices to answer three primary questions: (i) How do the impacts of pruning on the management of shoot blight compare between a vertical-axis orchard with mature trees and a high-density planting with young trees? (ii) Do sanitation and ancillary chemical management have a significant impact on shoot blight control achieved through pruning? (iii) How do a variety of pruning programs, including those preferred by researchers, growers, and extension agents, compare in terms of shoot blight management? The impacts of pruning programs were more pronounced in the vertical-axis orchard in terms of reducing infection spread and overall shoot blight incidence. However, in the high-density plantings, pruning programs were mostly ineffective and fire blight spread quickly throughout the trees and planting. Overall, the most aggressive pruning programs, which removed tissue of several seasons of growth, had the greatest impact on fire blight in both plantings. In line with the findings of many previous studies, sanitation or chemical management supplementation was not found to be necessarily beneficial.

Fire blight, a disease of pome fruits caused by the bacterium Erwinia amylovora, has become increasingly difficult to manage after the emergence of streptomycin-resistant strains. Alternative antibiotics and copper are available; however, these chemicals have use restrictions in some countries and also can carry risks of phytotoxicity. Therefore, there is growing interest in biological-based management options, with bacteriophage (phages) showing promise, as these naturally occurring pathogens of bacteria are easy to isolate and grow. However, there are several technical challenges regarding the implementation of phage biocontrol in the field, as the viral molecules suffer from ultraviolet radiation (UVR) degradation and can die off rapidly in the absence of the host bacterium. In this work, we assessed the efficacy of Erwinia phages and a commercial phage product for blossom blight control in the field across multiple locations in the eastern United States. In these tests, disease control ranged from 0.0 to 82.7%, and addition of a UVR protectant only resulted in significantly increased disease control in 2 of 12 tests. We also analyzed microbial community population changes in response to phage application. Changes in bacterial community diversity metrics over time were not detected; however, relative abundances of target taxa were temporarily reduced after phage applications, indicating that these phage applications did not have deleterious effects on the flower microbiome. We have demonstrated that biological control of fire blight with phages is achievable, but a better understanding of phage−pathogen dynamics is required to optimize disease control efficacy.