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ARS Home » Northeast Area » Frederick, Maryland » Foreign Disease-Weed Science Research » Research » Publications at this Location » Publication #375287
Research Project: Identification, Biology, Epidemiology, and Control of Foreign and Emerging Fungal Plant Pathogens

Location: Foreign Disease-Weed Science Research

Title: Rooting response of boxwood cultivars to hot water treatment and thermal sensitivity of calonectria henricotiae and C. pseudonaviculata in diseased boxwood

Author
item Shishkoff, Nina
item CUBETA, MARC - North Carolina State University
item MILLER, MEGAN - Illinois Soybean Association

Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2020
Publication Date: 3/23/2021
Citation: Shishkoff, N., Cubeta, M.A., Miller, M.E. 2021. Rooting response of boxwood cultivars to hot water treatment and thermal sensitivity of calonectria henricotiae and C. pseudonaviculata in diseased boxwood. Journal of Environmental Horticulture. 39(1):1–10. https://doi.org/10.24266/0738-2898-39.1.1.
DOI: https://doi.org/10.24266/0738-2898-39.1.1

Interpretive Summary: Boxwood blight is caused by the fungal plant pathogen Calonectria pseudonaviculata in the United States, where the disease appeared in 2011 and is currently reported from 28 states. In Europe the disease is also caused by a second species of Calonectria. Both pathogens are of great concern to the US boxwood nursery industry, whose yearly wholesale market value was estimated at $103 million prior to the identification of the disease in the US. The pathogen moves in the nursery trade with the transport of infected plants, so any method that promotes the production of clean plants would benefit growers across the country. In this study, the use of hot water treatments was evaluated to kill the pathogen in host leaves and twigs. However, it was unknown if hot water treatments would reduce the vigor of cuttings and affect rooting. Fungal growth from infected leaf tissue was reduced significantly after a 25 to 30 minute exposure in 47.5 C water or 12 minute exposure in 50 C water. After 8 minutes of exposure in 52.5 C water, little or no sporulation was observed for either fungal species. Most boxwood cultivars could withstand 60 minutes of exposure to 47.5 C water. With careful attention to the cultivar of boxwood being treated, hot water immersion could be part of an integrated pest management system for propagating boxwoods.

Technical Abstract: Boxwood blight is caused by Calonectria henricotiae (Che) and C. pseudonaviculata (Cps). Unrecognized symptoms on cuttings used for propagation can provide a source of inoculum. In this study, boxwood cuttings of cultivars ‘Justin Brouwers’, ‘Nana’, ‘Green Beauty’, and ‘Green Velvet’ were assessed for root production after exposure to 45 or 47.5 C water for 0 to 60 minutes at 5 minute intervals. The number of roots greater than 1-cm in length produced by cuttings three months after treatment in 45 C water for up to 60 minutes was not statistically different than for the non-treated control. A similar response was observed for cuttings of all cultivars treated in 47.5 C water for up to 60 minutes, except for cv. ‘Nana’ which produced fewer roots than the non-treated control after 35 minute exposure in heated water. Experiments conducted on diseased, detached boxwood leaves of susceptible cultivar ‘Justin Brouwers’ at 47.5 C, 50 C or 52.5 C significantly reduced conidia production and viability of Che and Cps after 25-30 minute exposure in 47.5 C water or 12 minute exposure in 50 C water. After 8 minutes of exposure in 52.5 C water, little or no sporulation was observed for either fungal species.