Detection and Quantification of Latent Infection by <i>Fusarium graminearum</i> , Causal Agent of Fusarium Head Blight on Hemp ( <i>Cannabis sativa</i> ) Fields in Kentucky

Fusarium Head Blight (FHB) can result in severe blighting of hemp grain and floral tissues. A multi-site field trial was conducted in 2022 and 2023 that included 3 different hemp cultivars with varying flowering time (early-, mid-, and late-flowering) and eight planting dates to detect and quantify early infection by <i>F. graminearum</i>. Asymptomatic terminal buds, female flowers, and/or male flowers were collected every 2 weeks beginning 2 to 3 weeks after planting and continuing until FHB symptoms were observed or plants reached maturity, resulting in 10 to 12 sampling dates per field. To detect and quantify <i>F. graminearum</i>, samples were subjected to a species-specific qPCR assay. Treatments including planting date and cultivar resulted in different levels of latent infection in each year and at each location. Despite latent infection being observed in vegetative tissues, infection was more prominent during flowering stages, indicating the importance of flowers for infection. Detections also appeared to be related to environmental factors such as rain and relative humidity. FHB symptoms were commonly observed 6 to 8 weeks after initial detection. Determination of when <i>F. graminearum</i> infection occurs in the field will help identify critical FHB management windows for hemp producers.