Determination of the Resistance of Tolerant Hybrids of Buxus to the Pathogen Cylindrocladium buxicola and the Effect of Nutrition and Climatic Conditions on Leaf Color

Boxwood (Buxus sp.) plays a key role in historical gardens due to its evergreen foliage and resilience. However, recent outbreaks of disease caused by fungal pathogens such as Calonectria spp. (C. pseudonaviculata, C. henricotiae) and Pseudonectria spp. (P. buxi, P. foliicola), as well as pest pressures from Cydalima perspectalis, have led to significant losses. This study examined 100 boxwood plantings across the Czech Republic to evaluate pest and disease occurrence. Further, six modern boxwood cultivars from the groups of BetterBuxus® and NewGen® were tested in field trials under the climatic conditions of the Czech Republic, focusing on their resistance to abiotic stress and foliage color retention throughout the year. Laboratory trials confirmed all cultivars were susceptible to C. pseudonaviculata, with ‘Renaissance’ showing the slowest disease progression. Field assessments under two contrasting management regimes (“Minimalistic” and “Pampered”) indicated sporadic boxwood blight incidence but frequent Volutella blight outbreaks, particularly where plants suffered frost stress. Leaf color, an important esthetic trait, was evaluated using Munsell charts and measuring the relative chlorophyll content. ‘Skylight’ most closely matched Buxus sempervirens in the shade of green and winter color.