This is a major issue we are seeing currently, especially here in Central Florida. Our weather went from one extreme to the other. We had months without a drop of rain, and now we are getting too much rain too quickly. And the temperatures have been climbing as well. The combination of this results in the disease pictured above. Grey Leaf Spot.
When we get excessive rains causing the grass blades to stay wet for 12 hour straight or longer, and temperatures in the 80s and 90s, it will cause this disease. Symptoms will continue to get worse as the lawn gets more and more wet. But it doesn’t have to just be constant rain for this to occur. If the humidity is over 95% for long periods of time, it will also trigger this disease to rear its ugly head.
Many people will make the mistake of thinking this is just a weak spot in the lawn and try to use a nitrogen fertilizer to push new growth. Never use nitrogen based fertilizer on an area of fungus. This will only ignite the disease and cause it to melt out and magnify the damage.
The best management practice for this is to use a fungicide labeled for control of this disease. Remember, the LABEL IS THE LAW! It is illegal to use any product outside the perimeters of what is stated on provided label. So make sure to read carefully before you use anything, and make sure to apply at the correct rate. Over applying will not solve your issue any better or quicker. That being said, the most effective fungicides for this certain disease are Strobilurin based, such as Heritage, Strobe, or Insignia. Ive tried other types before, but have had the most success using these. I highly recommend that you seek help from a professional lawn company when trying to deal with Grey Leaf Spot. They will have the proper equipment and products to take care of it effectively and efficiently.