Final Thoughts on Snow Mold This Spring

All of our snow mold trials have been rated this year. In our most southern site in Milwaukee and in Minneapolis, MN, snow mold did not develop. However, in Stevens Point, WI, Marquette, MI and Brainerd, MN we had phenomenal pressure. Especially at our Marquette site, which is shown in the image on the right. So I don't beat a dead horse too much, the idea with snow mold control is to mix products or use pre-mixed products. Mixtures of two or three of the following active ingredients, trifloxystrobin, iprodione, triticonazole, myclobutanil, propiconazole, thiophanate-methyl, chlorothalonil or fludioxonil, performed well at all of our sites. Check our website in a couple of weeks for this year's results! And if you are in the area stop in at one of our Snow Mold Field Days- April 14th (Brainerd, MN) April 15th (Stevens Point, WI) and April 16th (Marquette, MI). Please get in touch with myself or Paul Koch (plkoch@wisc.edu) if you would like specific information about these events.

The issue with snow mold control I do want to address is breakthrough. Many individuals experienced breakthrough with some products that traditionally do exceptionally well in our trials. So what is going on? I believe it is a timing issue. In our trials we typically apply fungicides at least two weeks prior to snow cover and many times a month prior to snow cover. Typhula sclerotia (survival structure) are thought to germinate when soil temperatures reach 32 F or soon after snow fall and then the mycelium would initiate an infection. So you are probably thinking then it is best to wait as long as possible to apply fungicides for snow mold control. Well that may not be the case. Recent research at UW-Madison regarding fall nitrogen applications shows that only 10 % of the nitrogen applied in November actually makes into the turfgrass plant. Transpiration is minimal during this time, therefore acropetal penetrants are likely not moving within the plant. Remember that acropetal penetrants like propiconazole, myclobutanil and thiophanate-methyl, enter the plant move in the xylem with the transpirational stream.

Basically when applications are applied very late in the year, the fungicide is likely only on or within the cuticle layer and not within the plant. If coverage is poor or infection occurred prior to snow fall (as is likely the case with Microdochium nivale), then a bit of breakthrough will occur. Then each year breakthrough occurs, inoculum levels will increase and eventually the chemical practice implemented is overwhelmed. All of this is just thinking out loud, but my predecessor Dr. Gail Worf always recommended applying fungicides for snow molds before deer season (Gun) opens in Wisconsin. This is normally the third weekend in November, which is typically 2 to 5 weeks before snow fall (that persists) in the Madison area.

We are doing some research to shed some light on these questions I have raised. One of my students Paul Koch, is examining the degradation rate of the fungicides chlorothalonil and iprodione in the absence and presence of snow cover. He has found that we can expect disease suppression with these two products for at least 28 days in a winter environment. We have yet to detect a difference between degradation rates of these two fungicides in the absence or presence of snow cover. Admittedly however, we are still doing some data crunching and this may change once our statistical analysis is completed. Then this fall we are going to conduct a fungicide timing study to determine when snow mold fungicides should be applied. In this study we will use a small number of fungicides representing at least one contact, systemic and a mixture of both types of fungicides. We have not worked out the exact details at this time, so any comments would be appreciated!

Besides snow mold, we have seen a few odd problems this spring. One in particular was fairly severe damage from what appeared to be fairy ring on a stand of Kentucky bluegrass grown on pure sand. The stand symptoms were necrotic rings with an orange tint and a strong mushroom aroma to the thatch layer. When we incubated the sample, a fungus with large clamp connections popped out the thatch. The odd thing about this problem, was the necrotic rings were present immediately after snow melt. There was type II fairy ring symptoms in this field prior to snow cover, so maybe the dark green areas were more susceptible to winter injury is my theory. Maybe others have seen this with fairy ring or maybe I was totally off with my diagnosis, once again any thoughts or comments on this would be appreciated. Next Wednesday is one of our Snow Mold Field Day dates, so I will likely not post anything. Hopefully I will see some of you there!