How Fungicides Affect Turfgrass Phylloplane Microbes.

Diseases are of paramount importance to golf course superintendents, especially with regard to putting green management. Periodic fungicide applications are needed to keep diseases suppressed.  Though, it is not known if the use of these fungicides impact the epiphytic microflora living in the phylloplane of the turf.  The objective of this 2-yr research trial was to evaluate the impact of cumulative fungicide applications (chlorothalonil, fluazinam, fluxapyroxad, fosetyl-Al, and pyraclostrobin) on the phylloplane microflora.  These fungicides were applied every 14 d to five different test plots with a sixth plot serving as a non-treated control.  Five days post treatment, four randomized replicate samples were taken from each treatment plot.  Replicates were separately homogenized in 1 mL of sterile DI water, diluted to concentrations of 10^-3 and 10^-5, and plated onto four separate isolation media [actinomycete isolation agar, acidified potato dextrose agar, nutrient agar + 1% sucrose, and King’s B(fluorescent pseudomonas isolation agar)].  Colony forming units (CFUs) were enumerated 2 and 7 d after plating and normalized to the sample weight.  In 2013, fluazinam raised populations of actinomycetes while fluxapyroxad lowered populations of fluorescent pseudomonads.  Surprisingly, fluazinam lowered populations of actinomycetes in 2014.  Chlorothalonil lowered fungal and actinomycete populations in 2014, when fungal populations were also lowered by pyraclostrobin.  Bacterial populations were also lowered by fluazinam in 2014. While results from this research help to identify fungicide impacts on culturable microbes that inhabit turfgrass putting greens, future research utilizing next-generation sequencing will broaden our ability to study entire microbial communities that inhabit various turfgrass ecosystems.