Page 12 - GreenMaster Fall 2022

Figure 3. Snow mould development at Timber Ridge GC in Minocqua, WI, following applications of Instrata made the previous fall at 6 different timings.
stand (which in Wisconsin would be late November). However, given all the changes in our climate over the past 30 years, it’s not clear if that’s still the best practice.
My program initiated a study back in 2016 to investigate the optimal timing of snow mould fungi- cides, with the goal of creating a model that would predict the optimal timing based on the local environ- mental conditions so far that fall. The study is pretty simple, we apply Instrata at 296 ml per 100 sq m once at 6 different timings throughout the fall based on when ‘traditional’ snow cover is for a particular location. The timings were 0, 2, 4, 6, and 8 weeks prior to traditional snow cover, and then we had a floating treatment that was intended to be applied as close to snow cover as possible that year.
This study was conducted in northern Wisconsin (Timber Ridge GC in Minocqua), central Wisconsin (Wausau CC in Wausau), and southern Wisconsin (OJ Noer Research Facility in Madison) and the traditional snow cover dates chosen for each site were November 1st, November 15th, and December 1st, respectively.
The location in Minocqua has had the most consistent disease so I will focus on those results. In each year, there was a date where a sharp cutoff from no control to good
control occurred, though this date shifted from year to year based on the conditions that fall. For example, in most years, the transition from no control to good control occurred between the October 15th application and the November 1st application, but in 2018-2019 the transition occurred between October 1st and October 15th due to a colder fall (Figure 3).
What this data suggests is that there is a ‘window of opportunity’ for snow mould control that is approximately 3-4 weeks long leading up to snow cover, and the decline in control at the front end of that window is very sharp. In 2019-2020, a difference of just 12 days in the application made the difference between a very effective application and almost no disease suppression (Figure 4).
The likely reason for the decline in control on the front end is that the snow mould fungi are not yet actively growing at the time of application, and the product degrades by the time the fungi do start to grow. We are currently working with a number of environmental parameters to predict when this ‘window of opportunity’ will occur for any location in the world based on their environmental conditions in the fall.
IRON SULFATE FOR SNOW MOULD CONTROL
Due to the great work done by the Oregon State University team of Alec Kowalewski, Brian McDonald, Clint Mattox, and many others, we already know that iron sulfate can provide effective suppression of Microdochium patch in areas like British Columbia that have prolonged periods of cool, wet weather but that don’t experience long durations of snow cover. The lack of snow cover allows for regular reapplications of iron sulfate to occur through- out the winter, something that’s not possible in areas that experience signif- icant snow cover.
My program had previously researched the ability of iron sulfate to control snow mould in areas with extended snow cover and found that one
12 • CGSA • GreenMaster