Potassium Applications as We Move Toward Later-Fall

[andy10917]

As we move into October, the question about whether or not applications of fertilizers containing Potassium are potential promoters of Snow Mold over the Winter, and may discourage recovery in Spring arises again. There are a few studies that indicate that it does.

Here's a clipping from Cornell University's turfgrass writeups, after a three year test:

Gray and pink snow mold infestation was assessed twice during spring 2008 by estimating the percent area per plot infected. As observed in previous seasons, the incidence of snow mold was increased at increasing potassium application rates. In fact there was a significant effect of the late season potassium rate on snow mold incidence, i.e., as late season rate increased snow mold incidence increased. There was also an obvious reduction in recovery associated with high seasonal and late season potassium applications.

I personally play things conservatively on cool-season grasses in this area, and don't include Potassium applications as a recommendation for annual plans I write for applications after October 1st. While I'm not sure the evidence is overwhelming, there are plenty of other opportunities in the April - September period to get the soil levels right, and I don't like rolling the dice. I don't think a few percent of Potassium in fertilizers in the Fall is a major issue, but full-blown quantities I avoid, and I recommend avoidance to others.

[MorpheusPA]

The probability was good on that, but the actual increase in amounts of snow mold modest--and the data set too small to make much of a conclusion. Anecdotal data indicates that my soil's loaded with potassium but the grass has almost no snow mold.

Still, like you, I do the same. Cutoff for most northern states at October 1. For transition states, October 15 is fine. In cases of extreme potassium shortage (which is rare), I may push northern states a bit later. But not much.

[rydaddy]

My last potassium went down last weekend (9/22). I am a member of the secret society of S.O.P. In that I have to "...locate 0-0-50 sulfate of potash"" every year after my soil test. With the struggles I have (on my lawn) I stop applying potassium before October as well - not worth the risk.

[ken-n-nancy]

There have been some continuing studies on potassium and snow mold by Doug Soldat at the University of Wisconsin at Madison. Below is a pic from a couple years ago from a twitter post:
https://twitter.com/djsoldat/status/712 ... 92/photo/1

Doug Soldat
No K on left, 0.1 lbs/1000 every other week on right.
6:56 AM - 23 Mar 2016
]/quote]

[TimmyG]

And then there's Doug's tweet from Feb 2017.

Doug Soldat
More snow mold than ever this year. Left: no K for six years. Right: 0.2 lbs K every other week. A4 bent
7:35 AM - 20 Feb 2017 from Wisconsin, USA

[PW405]

How long does turf need to be snow covered before snow mold becomes a risk?

[HoosierLawnGnome]

We don't regularly get extended snow coverage and I still hold off on the K. I don't remember the specifics but there was definitely a correlation between length of coverage and incidence of snow mold. More of a curve then a sudden spike at a particular number.

I did get it one year at our former residence, likely made more possible because coverage was extended due to shaded areas and big piles by the street.

[ken-n-nancy]

How long does turf need to be snow covered before snow mold becomes a risk?

I've usually seen phrases like 30-45 days or time frames like that.

The below article from Purdue says 40-60 days for mild symptoms, moderate levels for 60-90 days and severe damage possible for coverage of 90 days or more.

https://www.extension.purdue.edu/extmed ... -101-w.pdf

At least one month of nearly continuous snow cover happens pretty much every year here in Southern NH.

[andy10917]

55 days is the spike.