Relationship Between Phoma Black Stem Severity and Yield Losses in Hybrid Sunflower

Field trials were conducted over two growing seasons in South Dakota to determine the effect of artificial inoculation of hybrid sunflower (Helianthus annuus) with Phoma macdonaldii seed yield and other agronomic characters. Treatments were a factorial arrangement of inocula (sterile water or 2×10 5 conidia per milliliter of P. macdonaldii) injected into the lower stem and time of inoculation (2 wk before anthesis, anthesis, and 2 wk after anthesis), as well as an uninoculated check