In between looking a peanut maturity samples, a few commercial landscape managers brought in some turf to check for disease. With temperatures decreasing and high humidity, conditions are right for turf disease. Looking at a few samples of St. Augustinegrass, I found both Large Patch (Rhizoctonia solani) and Take-All Root Rot(Gaeumannomyces graminis). Take-All Root Rot can cause severe decline and usually results when pH is high. This St. Augustinegrass (above) was planted at the courthouse a few years ago. Initially there were problems with the grass yellowing. A soil test confirmed a pH above 7.5 which was result of liming material used during recent construction/renovation of the courthouse. This year, take-all is showing up. Under a dissecting microscope, you can see the mycelium on the stolon of St. Augustine (below).
When placed under a compound microscope, the hyphopodia, also called “puzzle pieces”, are the key ID feature of take-all patch (below).
In another sample, Large Patch was evident. These mycelium do not have hyphopodia. Three characterisitics of these mycelium are 1) Brown, septate hyphae (cross walls) 2) Mycelium branching at 90 degree angle 3) Tapering at the branch.
Long-term management of turf diseases are more practical. This includes aerating, dethatching, proper fertilization, irrigation etc. Aerating the lawn once of a few times during the growing season each year will allow oxygen and water to get to the roots and break up thatch which harbor disease and insects. Provide an inch/week of water between 9pm and 9am to reduce leaf wetness and provide efficient irrigation. When disease is prominent and fungicide application is necessary, UGA Extension Pathologist Dr. Alfredo Martinez recommends a fall and a follow up spring application of a recommended fungicide. Here is a table of fungicides from the 2014 UGA Pest Control Handbook.
More information on these diseases can be found at UGA Publication- Turf Diseases In GA: Identification & Control.