Field Performance of Buxus Cultivars and Selections Against Boxwood Leafminer and Boxwood Blight

Abstract

Boxwood (Buxus L. spp. Buxaceae) are popular landscape plants in the United States, with traditionally low maintenance requirements, glossy evergreen foliage, and deer resistance. Buxus sempervirens ‘Suffruticosa' (English boxwood) and B. sempervirens (American boxwood) were the most popular Buxus taxa planted for hundreds of years. But in the 1970s and 1980s, ‘Suffruticosa' lost popularity due to boxwood decline, and many commercial nurseries began to search for new cultivars. However, many of the popular new varieties, such as ‘Justin Brouwers', ‘Green Beauty', ‘Green Mountain', and ‘Green Velvet' were very susceptible to boxwood leafminer (Monarthropalpus flavus Schrank). In 2011 boxwood blight, caused by the fungus Calonectria pseudonaviculata, was identified in the eastern United States and Oregon. Based on early reports that both leafminer and blight were variety-specific, Saunders Brothers Inc., a wholesale nursery in Virginia specializing in boxwood, began field trials to search for cultivars with natural resistance to boxwood leafminer and boxwood blight. Reported here are field evaluations of 146 cultivars in leafminer trials and 75 cultivars and selections in blight trials. In these trials, cultivars ‘Peergold', ‘Cole's Dwarf', ‘SB 108’, ‘SB 300’, and ‘Wee Willie' and selections SB17 and 9-00-174 had low susceptibility (resistance) to both blight and leafminer. Species used in this study: Buxus harlandii Hance; B. microphylla Seibold & Zucc.; B. microphylla var. japonica D. Anberg; B. sempervirens L.; B. sinica var. insularis (Nakai) M. Cheng; Calonectria pseudonaviculata (Crous, J.Z. Groenew. & C.F. Hill); L. Lombard, M.J. Wingf. & Crous, 2010; Monarthropalpus flavus (Schrank). Buxus nomenclature according to Batdorf, 2021.