Combating an Invasive Boxwood Pathogen – Calonectria pseudonaviculata – in the United States by Shifting Production to Less-Susceptible Cultivars

Abstract

Boxwood Blight (BB) caused by Calonectria pseudonaviculata (Cps) is an economically devastating disease affecting the entire boxwood supply chain from growers to gardeners, since it was first officially documented in the United States in 2011. This disease has taken a heavy toll on boxwood, an iconic landscape plant and the number one evergreen nursery crop. The objective of this study was to examine the adoption of one sustainable management strategy available to growers: shifting boxwood production from highly susceptible to less susceptible cultivars. We investigated the ongoing shift by comparing boxwood sales of 17 selected nurseries from seven states across the country in 2011, 2016 and 2021. Results revealed that from 2021 to 2016, sales of cultivars highly susceptible to BB were reduced by over 35% while less sales of less susceptible boxwood cultivars increased 55%. Increased boxwood sales have been seen for ‘Winter Gem’, ‘Wintergreen’, ‘SB 300’ (Freedom®), ‘SB 108’ (Independence®), and ‘Little Missy’, all of which have been rated less susceptible than B. sempervirens ‘Suffruticosa’ in numerous trials. The potential for long-term positive impact on sustainable boxwood production and plantings in the U.S. through the use of such less susceptible cultivars is discussed. Better boxwood cultivar choices will build crop health into new plantings and sustain customer demand for boxwood. This is a case study for how sustainable crop protection strategy helps to maintain production of a crop under serious pressure from an invasive pathogen.

A Modified Delphi Study on Boxwood Blight Disease Management in the US Nursery Industry

“…Common cultivars such as Golden Dream, John Baldwin, Baby Gem, Wedding Ring, Sprinter, Green Pillow, Hohman's Dwarf, Grace Hendricks Phillips, Peergold, Cole's Dwarf, Big Leaf Wintergreen, and Green Pillow fall into Asiatic boxwood category (Baysal-Gurel and Liyanapathiranage 2017; Ganci 2014; Ganci et al 2013;Miller et al 2016;Yoder et al 2022). The results of this study are comparable to a previously published literature which indicates that the growers are shifting toward cultivating less susceptible boxwood (Omolehin et al 2022). Asiatic boxwood category includes high to moderately resistant cultivars whereas American/English boxwood category includes cultivars highly susceptible to boxwood blight.…”

“…Extent of the boxwood blight was ranked from 0 5 nonproblematic to 10 5 most problematic and the threat of the disease was ranked from 1 5 no threat to 5 5 extreme threat. Also, ordinal 5-point Likert-type scale (Likert 1932) questions were used to record the level of agreement in the modified Delphi survey (Ab Latif et al 2016;Mitroff and Turoff 2002) with the statements regarding the sources of plant pathogens and practices that limit and prevent plant diseases in boxwood production using a ranking from 1 5 disagree to 5 5 agree. The panel members were asked to rate their familiarity of processes and programs using a scale from 1 5 not familiar to 5 5 very familiar and additionally asked whether they currently follow those to control plant diseases to justify their responses.…”

“…The Delphi method used in this study was developed by RAND Corporation (Santa Monica, CA, USA) in 1950s Turoff 1975, 2002) and is based on using a series of data collection questionnaires and conducting several rounds of surveys to gain consensus from selected participants who have expert knowledge of the discipline (von der Gracht 2012). Also, the Delphi method is a structured communication process used to predict outcomes based on the past knowledge and experience of a group of experts (Mitroff and Turoff 2002). Delphi surveys are different from other types of surveys, as the expert panel has an opportunity to reconsider their answers anonymously based on the overall group responses (Mitroff and Turoff 2002).…”

“…Also, the Delphi method is a structured communication process used to predict outcomes based on the past knowledge and experience of a group of experts (Mitroff and Turoff 2002). Delphi surveys are different from other types of surveys, as the expert panel has an opportunity to reconsider their answers anonymously based on the overall group responses (Mitroff and Turoff 2002). Conventionally, the Delphi technique has been used as a forecasting method, communication improvement, or policy analysis technique.…”

US Consumers’ Awareness and Opinion of Boxwood Shrubs and Boxwood Blight

“…Further investigations to discern the alternatives consumers might prefer over boxwood are worth considering. As noted by Omolehin et al (2023) boxwood producers did not abandon boxwood but rather saw increased sales in less-susceptible boxwood cultivars, such as Winter Gem', 'Wintergreen', 'SB 300' (Freedom), 'SB 108' (Independence), and 'Little Missy'.…”