A proposed mode of action of oil-based formulations of a microbial herbicide

Formulation of some microbial herbicides in emulsions of vegetable oil can significantly reduce their dependency on long dew periods to allow infectio n and control of the host weed. Examination of leaves of Viola arvensis, by a range of microscopy techniques, after spraying with an oil-in-water emul sion formulation of the potential microbial herbicide Mycocentrospora aceri na, suggests that the effect arises as a result of inversion of water into both oil droplets on the leaf surface and oil that penetrates into the leaf tissue. This oil probably mixes with aqueous components from the leaf tiss ue and, in doing so, forms an invert emulsion. We suggest that this supplie s the water required by the fungus to initiate and sustain growth so that i nfection can result.