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- Author or Editor: Kumuditha Hikkaduwa Epa Liyanage x
Boxwood is one of the most popular evergreen shrubs in the United States, the production of which is currently challenged by boxwood blight, an emerging threat that has spread across 30 states. A thorough understanding of boxwood production, plant health, management practices and economic impact could aid in answering the needs of the nursery industry in managing this disease. An online modified Delphi survey was conducted to identify grower perceptions on processes, programs, and practices to limit or prevent the entry and spread of boxwood blight disease. The expert panel consisted of 29 nursery producers who represented a significant portion of boxwood production nationally. The panel members rated boxwood blight as the third most problematic disease with a potential to be number one in the future. Boxwood transplants were perceived as the main source of boxwood blight outbreak, followed by cutting tools, nursery equipment, containers, plant debris, irrigation water, worker hygiene, and other crops. According to the panel responses, cultural control methods, inspection, and quarantine of incoming plant material, scouting, and sanitization were the most important practices that can limit or prevent plant diseases during boxwood production. The panel members did not agree that the composted manure could influence the spread of plant disease in boxwood production, although this has been verified by the findings of various previous research experiments. Panel members were very familiar with scouting and employee training, best management practices, and the boxwood blight cleanliness program. This study documents the key components, practices, and procedures in boxwood production that could influence the spread of boxwood blight in nurseries and could be further verified by sampling and laboratory assays to specify the critical control points in the production process.
Early and accurate detection of diseases, and implementation of efficient disease management practices are crucial to reducing the economic impact associated with plant disease outbreaks. Based on survey responses from dogwood nursery growers in Tennessee, USA, scouting was identified as an important disease management practice adopted by a majority of growers for disease management in field-grown, container-grown, and pot-in-pot production systems. Our results show a significant positive correlation between disease severity and scouting frequency for dogwood plants grown in container and pot-in-pot production systems. Our efficiency measure is a self-rated efficacy scale perceived by the nursery growers about their existing disease management system in nursery plants. A significant positive correlation was found between the efficacy of disease management and the number of workers involved in scouting and a negative association between the worker hours spent in scouting and the grower's experience/exposure to other disease detection methods. The majority of nursery growers followed a set spray schedule between May and October, with applications scheduled every other week. In addition, our results showed significant positive correlations between efficacy and spray-related factors, such as disease severity and worker hours spent in spraying; efficacy of disease management and spraying frequency in field-grown dogwoods; and foliar spray costs and efficacy of disease management. We estimated ≈$379/acre per year average costs for dogwood disease management, which the growers find to be one of the major components of the dogwood production budget. Moving to automated systems of disease scouting and management has the potential to reduce the cost of these labor-intensive disease management practices of dogwood production.
The efficacy of the fungicide pydiflumetofen + difenoconazole (Postiva) was evaluated at varying application rates and intervals to control black spot disease (Diplocarpon rosae) in rose (Rosa spp. ‘Coral Drift’). Container-grown roses were arranged in a completely randomized design with five single-plant replications. Experiments were conducted under greenhouse and shade-house conditions (56% shade) in 2021/2022 and 2023. Black spot disease in roses was developed naturally. Pydiflumetofen + difenoconazole at 1.1 , 1.6, and 2.2 mL⋅L–1, and standard fungicide azoxystrobin + benzovindiflupyr (Mural) at 0.5⋅g L–1 were sprayed on foliage to runoff on a 2- or 4-week interval. Plants that were not treated with fungicide served as the controls. Plants were evaluated weekly for disease severity (0%–100% foliage affected) and defoliation (0%–100% defoliation). The season-long area under the disease progress curve (AUDPC) and area under the defoliation progress curve (AUDFC) were calculated for the evaluation period. Pydiflumetofen + difenoconazole reduced significantly black spot disease severity, AUDPC, defoliation, and AUDFC both in greenhouse and shade-house conditions compared with control plants, and was as effective as azoxystrobin + benzovindiflupyr. All the application rates and intervals of pydiflumetofen + difenoconazole were equally effective in reducing black spot severity and AUDPC. Our findings suggest that pydiflumetofen + difenoconazole at the lowest rate with the longest application interval is the most cost-effective, and has similar efficacy as treatments with higher rates and more frequent intervals.
The efficacy of the fungicide pydiflumetofen + difenoconazole (Postiva) was evaluated at varying application rates and intervals for the control of powdery mildew (Golovinomyces orontii, formerly Erysiphe polygoni) in bigleaf hydrangea (Hydrangea macrophylla ‘Nikko Blue’). Container-grown hydrangeas were arranged in a completely randomized design with six single-plant replications. Experiments were done in 2022 and 2023 under both greenhouse and shade house conditions (56% shade). Powdery mildew in hydrangea was developed naturally. Pydiflumetofen + difenoconazole at 1.1, 1.6, and 2.2 ml·L−1 and a standard fungicide azoxystrobin + benzovindiflupyr (Mural) at 0.5 g·L−1 were sprayed to runoff on 2-, 4-, and 6-week intervals. Plants that were not treated with fungicide served as the control. Plants were evaluated weekly for disease severity (0% to 100% foliage affected) and defoliation (0% to 100% defoliation). The season-long area under the disease progress curve (AUDPC) and defoliation progress curve (AUDFC) were calculated for the evaluation period. The initial and final plant height and width were recorded, and height and width increase were determined. Pydiflumetofen + difenoconazole and azoxystrobin + benzovindiflupyr significantly reduced final disease severity, AUDPC, and defoliation both in the greenhouse and shade house compared with control plants. In both greenhouse trials and the 2022 shade house trial, AUDFC was reduced in all treatments compared with the control plants. However, AUDFC was not reduced by all treatments in the 2023 shade house trial. Pooled over application intervals, the low rate of pydiflumetofen + difenoconazole was as effective as the medium and high rates of pydiflumetofen + difenoconazole and azoxystrobin + benzovindiflupyr in reducing final powdery mildew severity and AUDPC both in the greenhouse and shade house in both 2022 and 2023. No significant differences between application intervals were noted in final disease severity and progress. Control of powdery mildew with fungicides failed to increase plant dimensions (i.e., plant height and width) compared with the no fungicide control. Because all application rates and intervals of pydiflumetofen + difenoconazole provided comparable powdery mildew disease control, it is suggested that using a low rate of pydiflumetofen + difenoconazole with the longest application interval (6 weeks) is the most cost-effective approach for managing powdery mildew in bigleaf hydrangeas.