ABSTRACT Calonectria pseudonaviculata (Cps), a causal agent of the devastating boxwood blight disease in gardens and landscapes worldwide, produces conidia for dispersal and plant infection. However, its conidiation dynamics during disease development remain unclear. This study examined the conidiation ability and mycelial mass level of 21 Cps isolates from infected Buxus plants or fields in five US states on detached Buxus sempervirens ‘Suffruticosa’ leaves at 7 days post‐inoculation (dpi), resulting in three groups classified by principal components analysis (PCA) and K‐means. A time course study on the group representatives showed consistent lesion expansion but great variations in the sporulation dynamics at the commencement, peak and duration of conidiation; the conidium germination; and the initiation and germination of microsclerotia on the infected leaves. Specifically, representatives of groups I and II initiated conidiation at 4–6 dpi and peaked at 12–14 dpi with up to 350,000 conidia/cm 2 , while the commencement and peak of conidiation in group III were delayed 2–4 days, with a peak yield reduced by 40 times. Conidiation declined in all groups after the peak, but group III had substantially more dead conidia than groups I and II, even though it had live conidia after 60 dpi, like group I. Microsclerotia, like conidia, were observed first in groups I and II. They formed as early as 10 dpi, and their germination occurred at 20 or 30 dpi. Groups I and II, as greater sporulators, may have more advantages than group III in pathogen virulence and disease transmission.