Putting green problems: Stress, anthracnose, and Pythium root rot interactions
By Megan Kennelly, KSU Plant Pathology
We are coming into mid-summer which is the highest stress time of year for our bentgrass putting greens. We can get interactions of multiple stressors all affecting the turf, causing spirals of decline. Crown rot anthracnose is a disease that likes to kick in when the turf is stressed, such as when roots are damaged from hot, wet conditions. Pythium root rot also occurs when root systems are wet. We had a lot of drenching (even flooding!) rains in many areas in June. Soil sat wet, damaging roots. Now we have heat on top of that.
Healthy vs. damaged root systems
Take a look at photos 1 and 2 which show the washed off roots from some small plugs of putting green turf. In both, you will see that one plug has a much more robust root system than the other. In each photo, one set of roots looks okay, and the other is much reduced. Under the microscope, the damaged systems also show general discoloration and sloughing off of outer tissues. These symptoms mean the turf roots are in decline. The environmental stress alone can cause major root decline and turf damage.
However, on top of the physiological stress these samples were heavily infected crown anthracnose. Photos 3 and 4 show examples of what the anthracnose fungus looks like, showing the fungal structures. In addition, there was a light amount of Pythium root rot. That is a lot going on!
Anthracnose fungal structures on turf
Here is a link to a publication I’ve mentioned countless times on this blog: https://publications.mgcafe.uky.edu/files/PPA1.pdf
There are excellent sections on individual diseases including anthracnose (see detailed discussion of biology, cultural controls, and fungicides on page 9), but there is also a detailed section about summer stress on page 6. Many of the stress-reducing practices listed there will also reduce susceptibility to diseases.
That particular publication does not discuss Pythium root rot (PRR). (It does discuss Pythium root dysfunction (PRD) which is related but different.) Here is a great resource on PRR: https://www.turffiles.ncsu.edu/diseases-in-turf/pythium-root-rot-in-turf/
Managing the diseases is important, but it’s critical to address the physiological/environmental stresses as well or the turf can still suffer major decline this time of year.