Disease Triangle: If The Conditions Are Right…

disease triangle white snow

As it has been said many times about the Midwest, “If you don’t like the weather, wait a minute and it will change.” 

In mid-December, the temperatures were below zero and there were more than 6 inches of snow on the ground. One week later, the temperatures soared to a balmy 55 degrees on Christmas night and well into the next day. As I was writing this blog, the temperatures dropped back to normal December ranges at 24° F. It is supposed to warm up to the upper 30’s as the week goes on, so we are on a roller coaster ride of fluctuating temperatures.

In the past, I have written about what is required for a disease to develop also known as the Disease Triangle.

3 Points of a Disease Triangle

  1. Host plant
  2. A disease-causing organism
  3. An environment has to occur for a long enough time for the disease to develop and infect the host plant.

As I wrote earlier, on Christmas night the temperatures steadily rose to the mid 50’s by Monday morning.

This meant that the snow melted quickly and that there was a good deal of moisture available from the misty rain that fell Christmas day and into the night. It was also cloudy Monday morning.

All of these conditions are needed for Grey Snow Mold to develop. By mid-morning, I did see it begin to develop in my back yard. It may sound a little strange to say, but I was excited to see how quickly it developed. It stopped as quickly as it started as the sun came out, which stops the activity. So did the subsequent drop in temperatures overnight.

The amount of Snow Mold that did occur may have been minor, but the fungi remains in the lawn. When conditions are in alignment, it will start up again.

Then again, if the same conditions do not occur, it may not develop. One thing to remember about Snow Mold, either Grey or Pink, snow is not a requirement for it to develop. It just has to be above freezing, and cloudy with lots of available moisture to complete the third side of the Disease Triangle.

Pink and Grey Snow Mold

snow mold on grass

In my last blog post, I wrote about Snow Mold. I hadn’t really seen it show up yet when I wrote the blog, but within this past week, the disease has really started to show up. I was recently looking around my lawn, as most of the snow had melted and I found a good deal of both Pink and Grey Snow Mold occurring on my lawn at the same time. The temperatures had risen to the low 50s and the snow was quickly melting—two conditions that promote development of the disease.

pink snow mold on bermudagrass

In these pictures, you can see the strands of mycelium growing across the top of the turf. Again, it is usually not a serious disease, and it had completely dried out by Saturday. After winter, the grass was a little matted down, so I took a flexible rake and broke up the matted patches of grass. I did not want to rake too vigorously, as the ground was still wet and I did not want to damage the good grass.

Pink and grey snow mold is not just showing up in the northern states, however. I received the picture below from our franchise in Opelika, AL of a Bermudagrass lawn that had developed Pink Snow Mold. Actually, on warm season grasses, the disease has a much fancier name: Microdichium Patch. They have had cooler, wet weather in the South, which brought out the disease. Snow cover is not required for Snow Mold to develop. It can develop during cool, cloudy, and wet conditions, too.

Although this picture does not show the individual spots up close, snow mold is causing the lighter colored patches in the turf. But if you have matted grass after winter, know that it will recover, especially if the lawn is lightly raked.

For those of us in the North, we hope that the snow has ended for the year. We at Spring-Green are looking forward to begin servicing the lawns in our areas very soon, but we have to wait until the ground thaws. Watch for us in your neighborhood in the upcoming weeks!