Effectiveness and technological feasibility of bioherbicide candidates for biocontrol of Green Foxtail (Setaria viridis)

Green foxtail (Setaria viridis), one of the most common and troublesome weeds worldwide, is becoming very difficult to manage because of the lack of registered herbicides and the appearance of herbicide-resistant populations. Among the new and possible environment-friendly strategies, the use of biological control methods seems to have potential. Drechslera gigantea, Exserohilum rostratum and Exserohilum longirostratum have previously proved to be promising bioherbicide agents against several grass weeds in field trials. While previous studies have established the susceptibility of S. viridis under greenhouse conditions, so far no attempt has been made to establish the effectiveness and feasibility of these fungi as bioherbicides for green foxtail. When spore suspensions were applied as foliar sprays to green foxtail seedlings in a greenhouse, all three fungi caused severe damage by 1 day after application, and seedlings in most cases died within 1 week. The fungi were compatible with several agro-chemicals and host specific when tested against major vegetable crop species grown in the Mediterranean. The demonstrated technological feasibility of producing large amounts of quickly germinable conidia (i.e., asexual spores) on inexpensive solid media increases the potential of these fungi to be used as bioherbicides.