By: Brian McDonald, Oregon State University
As summer winds down and the temperatures drop, it is time to start thinking about Microdochium patch, especially on Poa greens (Figure 1). Note: I use the term “Microdochium patch” to describe the disease (Microdochium nivale) when it occurs NOT under snow cover, and I use the term “snow mold” to describe the disease when it occurs under snow.
The biggest concern is getting caught off guard by early fall rains. A fungicide application in late summer that controls anthracnose, but also has some activity on Microdochium patch, can save you from a fall surprise. Products like Banner Maxx, Densicor, Turfcide 400, Ascernity, and Tuque ExoGEM come to mind – all of which will suppress both diseases. Maxtima or Navicon would likely work as well, but they are not quite as effective on Microdochium patch as the other products. Navicon has the added benefit of having a strobilurin which will control yellow patch, which we often get in the fall in the Pacific Northwest. Headway (propiconazole + azoxystrobin) also works well for these three diseases.
If you want to go the “alternative products” route, you could supplement your anthracnose fungicide with Civitas mineral oil by itself, or combined with a phosphite, to get stronger suppression of Microdochium patch if you live in an area that has a lot of Microdochium patch pressure.
In areas like the Pacific Northwest, with as much as 9 months of Microdochium patch pressure, recurring fungicide applications are necessary. Instrata (a 3-way mix of propiconazole, chlorothalonil, and fludioxonil) is one of the strongest products we have and is commonly used along with the other fungicides mentioned earlier. Other notable products that are effective include Affirm (polyoxin D - quick acting, but shorter residual), Secure (fluazinam, a contact), and products with iprodione (26GT & Interface). Daconil (chlorothalonil) is effective, but I like to use chlorothalonil in the summer to control anthracnose and Secure to control Microdochium patch. Medallion SC (fludioxonil) has been effective at higher rates when mixed with other systemic fungicides. Since we do not get extended snow cover and we get play all winter, the goal is to avoid injury in the fall so you don’t have to stare at disease scars all winter waiting for warmer weather and the turf to heal.
If your Microdochium patch typically shows up later in the fall, many experienced superintendents use an indicator green or some other area of the golf course to time their first Microdochium patch application. Once they first see the disease on these susceptible areas, they immediately spray their putting greens. If you follow this approach, it is advisable to mix a contact and a systemic fungicide together for the first application. The danger with this approach is that your indicator green may have many more infections than are expressed when you first see the disease symptoms. These infections will show up in a few days after you have sprayed, which might make you think the fungicides did not work. Whether this is a concern depends on your tolerance for a little disease injury and whether there is enough warm weather in the fall to grow out of the injury before the cold weather comes.
While chemical control of this disease is required for full control, the WinterTurf program has a number of ongoing studies investigating non-chemical control options as well.