Combating an invasive boxwood pathogen – Calonectria pseudonaviculata – in the United States by shifting production to less susceptible cultivars

Authors: OMOLEHIN, OLANIKE - Virginia Tech; KELLER, JOHN - Monrovia; Gouker, Fred; DAUGHTREY, MARGERY - Cornell University; Luster, Douglas - Doug; PSCHEIDT, JAY - Oregon State University; HONG, CHUANXUE - Virginia Tech

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2022
Publication Date: 12/8/2022
Citation: Omolehin, O., Keller, J., Gouker, F.E., Daughtrey, M., Luster, D.G., Pscheidt, J., Hong, C. 2022. Combating an invasive boxwood pathogen – Calonectria pseudonaviculata – in the United States by shifting production to less susceptible cultivars . Plant Disease. https://doi.org/10.1094/PDIS-09-22-2124-RE.
DOI: https://doi.org/10.1094/PDIS-09-22-2124-RE

Interpretive Summary: Cultivar selection plays a significant role in sustainable crop production especially for plant disease management. For boxwood blight, it is unclear how studies on cultivar performance under severe blight infestation have led to changes in management of the disease in the United States since 2011. Multiple blight management approaches have been in place since blight became a devastating epidemic, but due to regulatory and economic issues, most of these approaches are not sustainable. The use of disease-resistant cultivars is the most sustainable, least expensive, and stable approach to managing crop diseases. In this study we surveyed 16 nurseries across seven states where boxwood was produced in 2011 and is still being produced despite severe boxwood blight incidences. We observed a gradual shift in sales from blight-susceptible boxwood cultivars to pre-existing or newly developed blight-resistant boxwood cultivars. The shift became pronounced in the most recent 2021 sales data, with a 93% increase in sales of more the resistant ‘Winter Gem’, ‘Little Missy’, ‘Independence’ and ‘Freedom’ cultivars. This shift to more resistant cultivars builds crop health into new plantings of this landmark plant and demonstrates sustained demand for boxwood, setting a new example toward sustainable agricultural and ornamental crop protection under increasing pressure of invasive pathogens and pests.

Technical Abstract: Boxwood Blight (BB) caused by Calonectria pseudonaviculata (Cps), an economically devastating disease affecting everyone in the supply chain from grower to retailer, landscaper, and consumer as well as public gardens, was first officially documented in the United States in 2011 and this disease has taken a heavy toll on boxwood, an iconic landscape plant and #1 evergreen nursery crop. Instead of abandoning boxwood production and switching to focusing on other evergreens, growers in the U.S. have elected to combat this disease through cultivar selection informed by the latest research. One of the strategies growers employed has been a shift in boxwood production and sales from highly disease susceptible to more resistant cultivars. The objective of this study was to investigate and further promote the ongoing shift by comparing boxwood sales of 16 selected nurseries from seven states across the country in 2011, 2016 and 2021, and discuss the possible long-term positive impacts on sustainable boxwood production and plantings in the U.S. Results reveal an additional 21.24% (93 percent increase) in sales of more resistant boxwood cultivars in 2021 compared to 2016. These included some of the more resistant cultivars experiencing an increase in sales which are ‘Winter Gem’, ‘Wintergreen’, NewGen ‘Freedom’, NewGen ‘Independence’, and ‘Little Missy’. This shift to more resistant cultivars builds crop health into new plantings of this landmark plant and sustains growth for demand of boxwood, setting a new example toward sustainable agricultural and ornamental crop protection under increasing pressure of invasive pathogens and pests.