Three Botrytis Species Found Causing Gray Mold on Industrial Hemp (Cannabis sativa) in Oregon

The bud rot pathogens infecting cannabis (Cannabis sativa L., marijuana) inflorescences: symptomology, species identification, pathogenicity and biological control

“…The most common pathogen associated with bud rot symptoms on cannabis and hemp grown indoors and outdoors, respectively, in British Columbia was B. cinerea, representing 88% of 178 isolates recovered from 10 sampling sites over 2 years of study. This confirms previous findings associating B. cinerea with bud rot symptoms (McPartland 1996;McPartland et al 2000;Punja et al 2019;Garfinkel 2020;Jerushalmi et al 2020;Thiessen et al 2020). Diseased samples with B. cinerea were recovered most frequently during September-February, months represented by cooler night temperatures and wet or humid daytime conditions, both of which are known to favour infection by B. cinerea on other crops (Jarvis 1962;Bika et al 2021).…”

“…Letters above bars denote significant differences using ANOVA followed by Fisher's LSD test at P < 0.01. period in the late summer and autumn seasons, and less so during the spring or summer months when greenhouse temperatures are >25°C and not conducive to pathogen growth. Similarly, under field conditions, bud rot symptoms are commonly seen in the autumn season (Garfinkel 2020). On alfalfa florets, the optimal conditions for infection by B. cinerea spores was 20°C and 12 h of surface wetness (Gossen and Lan 2021); no infection was observed at 30°C.…”

“…In addition to B. cinerea, a low frequency of B. pseudocinerea (two isolates) and B. porri (one isolate) were recovered from bud rot samples from two organic production sites. The former species was recently isolated from bud rot-infected hemp flowers in Oregon at a low frequency (two out of 23 isolates), and was shown to be equally virulent to B. cinerea (Garfinkel 2020). In the present study, isolates of B. pseudocinerea were identical in colony and spore morphology to B. cinerea, confirming previous reports (Walker et al 2011;Garfinkel et al 2019) but showed lower virulence on detached cannabis inflorescences.…”

“…Symptoms of bud rot on cannabis and hemp plants include decay of a portion or of the entire inflorescence, followed by characteristic sporulation of the pathogen. Despite previously published reports that the causal agent of bud rot worldwide is B. cinerea (McPartland 1996;Punja et al 2019;Garfinkel 2020;Jerushalmi et al 2020), there have been no studies conducted to confirm whether there may be more than one species of Botrytis infecting cannabis or hemp plants in Canada or whether other pathogens can produce similar symptoms. The period of time when infection occurs or how disease symptoms progress on affected inflorescences has not been studied.…”

“…These 'bud rot' pathogens are reported to include Botrytis cinerea Pers. Fr., a widespread and destructive pathogen of cannabis and hemp (Punja et al 2019;Garfinkel 2020), as well as several species of Fusarium and Penicillium that can cause pre-and postharvest bud rots (Punja 2021a(Punja , 2021b(Punja , 2021c. Infection by Hop latent viroid can also reduce the quality of cannabis inflorescences (Bektas et al 2019;Warren et al 2019).…”