More fungicide applications for snow mold control?

Over the past two weeks I received many calls regarding the mild conditions and concerns about effectiveness of fungicide applications for snow mold control.  The major question is whether or not to make another application at this time.  Consider he following:

  1. The snow mold of concern here in Indiana is pink snow mold, aka Micodochium patch–same pathogen with two phases of disease, one under snow, and one without snow cover.
  2. The pathogen is capable of growth within a broad window of temperature (32-50 Fahrenheit)…as long as there is ample moisture…and there has been.
  3. Effective fungicides perform best during the initial periods of pathogen growth.  So, if an effective fungicide combination (at appropriate application rates) (say DMI + iprodione + QoI +/-chlorothalonil, +/- PCNB) was applied in late November or early December, then it is likely that the fungicide was successful in reducing pathogen populations to very low levels.
  4. Fungicide applied 2-4 weeks ago is no longer present in the plant—at least not in amounts that can limit fungal growth.  Also, it is not present in thatch or soil.  Since temperature has remained unseasonably high (extended periods well above 40F), fungicides were broken down in plant tissues and in sand/thatch quickly—within 10 – 14 days.  Most of the residues are degraded rather than removed by mowing or washing with rain.  So, protection is weak at very best.
  5. Those populations that were reduced by fungicide application (in item 3 above) begin to regrow as soon as fungicide is depleted.  With the extended forecast for mild conditions, new infections are likely, and superintendents should consider another application of effective products on greens (and maybe tee boxes if grass is prone to infection and budget allows).
  6. There are many options to choose from, but I think a combination of active ingredients (including chlorothalonil) should be considered.  Also, remember that effective granular options are available (Headway G, Pillar G) to avoid compacting greens with a large sprayer.

As always, I would suggest a 3′ x 5′ check plot one of the more disease prone greens to learn the benefit of any supplemental spray.  That way, when this question arises again in the future, we have some compiled experience to serve as a reference.

Rick Latin, Turfgrass Pathologist

Tweet from Ryan Cummings about his second snow mold application on December 22.  https://twitter.com/RCummings38

 

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