The fungicide benomyl is the most commonly used biocide for both field and greenhouse experiments in which arbuscular mycorrhizal fungal (AMF) suppression is desired. Unfortunately, benomyl is no longer manufactured and is therefore not available for experimental use and no fungicide has been proposed as a successful alternative for experimentally suppressing mycorrhizal fungi. In this study, we examine the potential for the fungicide Topsin M^® (topsin) to suppress mycorrhizal symbiosis in both field and greenhouse experiments.

Results/Conclusions

Topsin reduced AMF colonization of the obligately mycotrophic, warm- season grass Andropogon gerardii, with a large and significant reduction in plant biomass production.  Topsin reduced AMF colonization of the facultatively mycotrophic, cool-season grass Pascopyron smithii but did not significantly reduce biomass production.  Fertilization with nitrogen and phosphorus was able to compensate for reductions in biomass due to the application of fungicide, as biomass production of plants that received topsin fungicide was not significantly different from fertilized controls not receiving topsin.  While we are not advocating that topsin fungicide is a universal mechanism for mycorrhizal-suppressed controls, in systems where benomyl was found to be successful, topsin appears to be a useful, available, and successful alternative.