Winter Fungicide Degradation

On intensively-managed golf course turfgrass in temperate climates, one or two fungicide applications are required in the fall prior to snowfall to suppress fungal diseases such as Microdochium patch (Microdochium nivale (Fr.) Samuels & I. C. Hallett) until spring.  However, winters with inconsistent snow cover may alter the persistence of turfgrass fungicides and render plants more susceptible to fungal infection.  This study was conducted to determine the effect of snow cover on the persistence of the fungicides chlorothalonil and iprodione on golf course turfgrass.  Both fungicides were applied once prior to snowfall to creeping bentgrass (Agrostis stolonifera L.) in Madison, WI for four consecutive winters beginning in 2009-2010.  Fungicide treatments were kept under continuous snow cover or maintained free of snow cover for the entire winter to determine the effect of snow cover on fungicide persistence (2010-2011 to 2012-2013) and disease development (2009-2010 to 2012-2013).  Snow cover resulted in faster iprodione depletion relative to no snow in two of three winters tested, likely due to rapid depletion during snow melt events.  Snow cover slightly decreased chlorothalonil depletion relative to no snow in one of two years.  Snow cover resulted in decreased Microdochium patch development in a controlled environment chamber during two of the four winters regardless of the fungicide and had no impact during the remaining two years.  In addition to the impact of melting snow, winter rainfall events in three of four winters resulted in rapid depletion of both fungicides and a subsequent increase in disease development.  In 2011-2012, both fungicides depleted rapidly during a warming trend in the absence of snow cover and rainfall, suggesting that temperature-influenced factors such as plant or microbial metabolism may also contribute to fungicide depletion in a winter environment.

University of Wisconsin-Madison