Improved bioherbicidal efficacy by Myrothecium verrucaria via spray adjuvants or herbicide mixtures

Herbicides and spray adjuvants were evaluated for compatibility with the bioherbicidal fungus, Myrothecium verrucaria. Several commercial formulations of glyphosate were found to be compatible for tank mixing with M. verrucaria, including Touchdown and RoundUp HiTech . Others, such as Accord XRT II and RoundUp WeatherMAX killed all the spores of M. verrucaria immediately after mixing at only 10% the maximum labeled application rate. Many herbicides, which were not suitable for co-application with M. verrucaria, did not inhibit the growth of the fungus when added directly to media at up to 1% concentration, indicating that these products could be compatible with M. verrucaria as sequential applications in an integrated weed management system. Several commercially available spray adjuvants and polyoxyethylene tridecyl ether (TDA) formulations were tested in vitro for their efficiency in dispersing spores and in a plant bioassay for bioherbicidal activity. All of the products improved the activity of M. verrucaria over the water-only treatments and TDA formulations with a hydrophilic–lipophilic balance (HLB) number of 8 or 10 had the highest activity. The mechanism for improved bioherbicidal activity with these adjuvants was investigated in vitro, and TDA HLB 8 and 10 did not significantly improve conidia dispersal or accelerate spore germination relative to other surfactants. It is possible that the role of the surfactant is in the alteration of the plant cuticle or otherwise preparing the infection court. Better adjuvant selection and integration with affordable synthetic herbicides should aid in the development of more cost-effective biological control of weeds. Published by Elsevier Inc.