Biological agents, including fungal pathogens, are being considered to control weeds such as dandelion. Compatibility of a fungal pathogen, Phoma herbarum, with nonformulated 2,4-D was tested in vitro. Moderate to high concentrations (828 to 2,451 ppm) of 2,4-D reduced fungal colony diameter by 50% or less, suggesting that practical concentrations may be chosen for tank mixes. Under growth room and field conditions, integration of 2,4-D and P. herbarum produced enhanced control of dandelion. In general, synergistic responses to sublethal doses of 2,4-D followed 4, 8, or 16 d later by P. herbarum inoculation were found. Synergistic interactions, as determined by the Colby method, ranged as high as 62% greater than expected for an additive interaction. In general, dandelion response was reduced under field conditions, suggesting that environmental conditions or other factors play a role in efficacy. Integration of chemical and biological agents shows potential for enhanced weed control.

Nomenclature: 2,4-D; dandelion, Taraxacum officinale Weber in Wiggers TAROF; Phoma herbarum.