Program '11: Lessons from 2010

The summer of 2010 was a rough one and an experience that nobody wants to repeat. While new problems like bacterial wilt received a lot of attention in 2010, in reality it was an old problem that caused the majority of damage to creeping bentgrass putting greens in North Carolina: Pythium root rot.


Pythium root rot is brought on by wet soil conditions; temperature doesn't matter. Since there are several Pythium species that can cause root rot, the disease can develop at any time of year as long as the soils are wet. We see Pythium root rot all throughout the year, and even diagnosed a case of it in western North Carolina last week.

Because it needs wet soils, Pythium root rot is most common in poorly drained greens. However, the disease can also occur in newer, well-drained greens if wet weather conditions persist for long enough. That's where spring of 2010 comes into play. Many areas in North Carolina experienced prolonged wet weather conditions during March and/or May, which triggered the development of Pythium root rot.

Our clinic was inundated with cases of Pythium root rot on creeping bentgrass during the first week of June. As soon as the weather turned hot, the plants with weakened, Pythium-infected roots were the first to decline. Most golf courses managed to survive through the initial heat wave in June, but hot and wet weather in July and August finished-off a lot of greens.

The problem is that most fungicide programs for creeping bentgrass greens include no fungicides for Pythium root rot until mid-June. Why wait until June? It's based on the misconception that Pythium diseases only develop during hot weather. We now know with 100% certainty that's not the case.


If you look at average daily rainfall in Raleigh, for example, you'll see that there is no pronounced wet season. Other than drier periods in April and late November, we get about 0.12 to 0.15" of precipitation per day on average from May through November. So when can we expect to see Pythium root rot activity? Any time between May and November, depending on when the rain comes in that particular year.

So what are you supposed to do, spray Pythium fungicides constantly from April through November? You could, but you'd be wasting a lot of money. The key is to adjust your fungicide program as needed during the year based on weather conditions: if it's wet, then treat the greens preventively for Pythium root rot. You simply can't write a Pythium root rot program on the calendar.

To find out more about Program '11, please visit our project website.