Question of the Week Number 1: July 26, 2018

“What is wrong with my St. Augustine? I’ve added iron and nitrogen. Nothing seems to help.”

Scott H. posted this photo to my Facebook page a couple of weeks ago. Others have been asking the same question repeatedly.

This is gray leaf spot. We’ve talked about it before here this summer. (See July 5 issue) However, it’s come up so many times it merits repeating.

This is a fungal disease that attacks St. Augustine during the hottest part of the summer. I describe it as creating “washes” of yellowed grass, as you can see in Scott H’s photo above.

Continued Below


However, to confirm its presence you have to look more closely at the affected areas, and that’s when you’ll see the diamond-shaped spots on the blades and occasionally on the runners as well.

Scott H. also posted this close up photo of his St. Augustine, and if you click to zoom in on it you will see the diamond-shaped, gray-brown lesions on the blades. Click image for larger view.

How to deal with gray leaf spot…
First and foremost, withhold all nitrogen fertilizer from your lawn during the summer. Nitrogen exacerbates this disease. Do not fertilize St. Augustine between mid-June and early September. It may be that gray leaf spot was unusually bad this year because of the early arrival of really high temperatures in June.

Apply a labeled turf fungicide to stop the current outbreak. Your local independent retail garden center will show you the products available for its control. However, I learned when this disease broke out in my own yard in the mid-1990s that avoiding nitrogen was far more effective than trying to treat with fungicides. I just spent 30 minutes online on various university plant pathology websites, and they repeated that suggestion several times over.

Want to know how to tell gray leaf spot from chinch bug damage (since both are active right now)? This is chinch bug attack. Look beyond the totally browned grass around the tree stump – out into the lawn. You’ll see how it first appears. See my information from e-gardens last week. (Steph C’s photo posted to my Facebook page last week.)

Posted by Neil Sperry
Back To Top