Interaction of a bioherbicidal fungus with a phenoxy herbicide for controlling velvetleaf (Abutilon theophrasti).

The fungus, Fusarium lateritium Nees ex Fr. (FL), has shown potential as a bioherbicide for velvetleaf (Abutilon theophrasti Medik.) control. However, to achieve optimal infection and weed mortality, bioherbicide applications must be applied to weeds that are in the cotyledonary growth stage, followed by a dew treatment of at least 16 h. Greenhouse and field experiments were established to discover possible synergistic disease interactions with a phenoxy herbicide to improve the bioherbicidal potential of this fungus, and to mitigate some of the physical and environmental restrictions that limit the utility of this fungus as a bioherbicide. In greenhouse experiments, mortalities of 94% and 94% were recorded from sequential applications of 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] (0.02 kg ae ha−1) followed by FL (1.5 × 106 spores ml−1) at 5 min or 7 days after herbicide treatment. Velvetleaf plants in the fifth-to-seventh leaf growth stage were infected and killed with < 8 hrs. of dew. Similar results occurred under field conditions. Infection and weed control were inhibited by tank mixtures of 2,4-DB and FL, and by sequential applications of FL followed by 2,4-DB. These results suggest that timely applications of 2,4-DB followed by F. lateritium may provide effective control of velvetleaf. [ABSTRACT FROM AUTHOR]