Factors Affecting Plant-to-Plant Spread of Calonectria pseudonaviculata Through Pruning Shears

Calonectria pseudonaviculata (Cps), a causal agent of boxwood blight, produces sticky conidia as dispersal and infective propagules. These conidia readily adhere to tools that come in contact with diseased plant materials. However, plant-to-plant spread via pruning shears has been considered inefficient. Here we used hand-held pruners and two susceptible cultivars – Buxus sempervirens ‘Justin Brouwers’ and ‘Suffruticosa’ as detector plants to further evaluate the efficiency of this pathway. This study demonstrated that wetting inoculum plant foliage increased Cps spread onto detector plants via pruners. The spread further increased with increasing number of cuts on inoculum plants prior to cutting detector plants. Between two highly susceptible detector cultivars, Suffruticosa, with much more new growth and leaves at the time of this study, had greater blighted leaf counts than Justin Brouwers. These results suggest that Cps spread via pruners could be highly efficient, depending upon the wetness of and number of cuts on inoculum plants, and the amount of new growth on detector plants. These findings advance Cps dispersal biology with important practical implications, particularly in gardening and ground maintenance as boxwood requires regular pruning for prized use as hedges, parterres, landscape groupings, and topiaries.