Lawn Fungus: How to Prevent It and What to Do If You Have It

It’s that time of year again. Temperatures are cooling off at night and daytime temperatures are slightly cooler with a few hot days scattered here and there. What does this mean for those of you who maintain your own lawn? Fungus is ready and waiting to show its face in your lawn.

“The first thing to know is that fungus is 100% preventable.” says Phillip Hisey, On Top of the World Communities' Landscape Superintendant. “For fungal pathogens to become active in the landscape, a few environmental factors must be present.

First, the temperatures have to be between 65 and 85 degrees. Second, soil moisture has to be at higher levels. The fungal pathogen is already in the soil but without these factors is not likely to spawn and become problematic.”

Hisey says there are three fungal pathogens that are most likely to create problems in your home lawn. The first is Rhizoctonia solani; also known as Large Patch fungus. Another is the Gaeumannomyces graminis var. graminis, also known as Take All Root Rot and the last is Pythium Root Rot.

With the proper treatment program these are 100% preventable. “Another thing to remember is that when treating fungal problems, fungicides work better at lower preventative rates rather than at the curative rates. Once you start using curative rates, damage has been done and recovery is slow.” explains Hisey.

Rhizoctonia solani, also known as Large Patch fungus, is probably the easiest to identify by the “halo” or distinct yellow margin that forms. Another way to identify the fungus is to run the palm of your hand across the potentially infected area and see if the leaf blades come off. If you have the fungus, the leaf blades or sheaths will break off easily. Preventative applications are preferred but if you are trying to save the grass that has been infected, using a systemic fungicide is the best bet. “Systemic products are taken up through the plant while contact fungicides actually come into contact with the pathogen.” says Hisey.

Gaeumannomyces graminis var. graminis or Take All Root Rot has been problematic in the past as well. Most people didn’t realize they had it while some found out when it was too late. Again, preventative applications are the key to success for controlling this fungal pathogen. One of the key factors when dealing with this fungus is soil pH.

“Using acid forming fertilizers to lower soil pH will help. This fungus prefers pH levels above 7.0. So avoid late season fertilizations and check your irrigation system for proper coverage and see that you are not applying too much water.”

Pythium is a bit easier to control because most of the triggers for this fungus are culturally related or depend on things we can control such as avoiding excessively wet roots and trying to avoid stress to the grass. Products should be applied in a preventative method. “If you have not made any applications to your lawn, now is the time. Large Patch fungus should be treated in the fall, starting now through November, and should pick up again in March and April. Take All Root Rot should be treated preventatively in October through November, again in January and February and possibly again in March if winter temperatures persist.” explains Hisey.

With Take All Root Rot, trying to get a lower pH is the key to success so applications of fertilizer in the spring should have higher levels of sulfur. Coming out of the winter, if you suspect the Take All Root Rot has infected your lawn, use liquid applications to fertilize the grass “Remember the roots have been damaged and therefore are not taking up the nutrients vital to growth.” And lastly, if you are following these applications for Large Patch and Take All Root Rot you are very likely taking care of the Pythium.