Page 10 - GreenMaster Fall 2022

10 • CGSA • GreenMaster
Figure 2. These results depict the amount of pink snow mould and the concentration of chlorotha- lonil present in plots that were kept covered in snow or free of snow during the winter of 2012-2013 in Madison, WI.
To better understand the factors that influence persistence of snow mould fungicides, we conducted a series of experiments in Madison, WI, beginning in 2009 to test how snow cover impacted persistence of iprodione and chloro- thalonil. We applied both fungicides shortly prior to permanent snow cover and then kept certain plots free of snow and others covered in snow throughout the winter and regularly sampled the plots to measure the concentration of both fungicides in the turfgrass leaves.
To our surprise, snow cover had very little direct impact on how long both fungicides persisted throughout the winter (Figure 2). The much larger factor that influenced persistence was winter rainfall or snowmelt events. Anytime a significant rainfall event occurred, or warmer temperatures led to a significant snow melt event, the concentrations of both fungicides plummeted, which led to increasing levels of pink snow mould when we inoculated them in the growth chamber. In Figure 2, multiple rainfall events occurred in mid-January of 2013 and led to the rapid decrease in chlorothalonil concentration.
However, this doesn’t necessarily mean that fungicide retreatments are required any time it rains during the winter. In fact, in most cases they aren’t required. The reason is that the most significant impact of your snow mould fungicide is at the time of application when it knocks back the snow mould fungi, not by persisting throughout the winter. The rare cases where a reappli- cation might be beneficial is when the rainfall or melt event occurs very shortly after the fungicide application, and/or if it occurs in regions where very heavy snow mould pressure is common.
OPTIMAL SNOW MOULD FUNGICIDE TIMING
One of the most common discussions among golf course superintendents in my region is when do they plan to apply their snow mould fungicides. Professor Gayle Worf was the University of Wisconsin Turfgrass Pathologist for decades leading up to the 1980’s, and he always told Wisconsin golf course superinten- dents to have their snow mould applications down before they got in the deer