Q: I have been battling a fungus on my grass all summer and I was curious if you could help me fight it. I have been told I have leaf spot disease on my St. Augustine grass. Can you help?
A: Gray leaf spot (Pyricularia grisea) goes with St. Augustine like grits go with shrimp! Or like chinch bugs go with St. Augustine! To battle gray leaf spot you are best employing many cultural practices and using limited control products if necessary.
Gray leaf spot looks like someone burned or dripped acid on the leaves of the plant.
There are little oblong spots on the leaf.
Eventually, these spots grow together and the leaf blade dies.  Whole areas of your grass can disappear at once when these leaf blades die.
Culturally there are several things to do to minimize your problem with gray leaf spot.  This disease likes high humidity and excessive nitrogen fertilizer.  To help alleviate the high humidity, mow your grass to a level that seems abnormal to St. Augustine.  Try to get it down to 2 - 3 inches depending on the variety of St. Augustine grass.  Also try to mow every 3 – 5 days with a bagger.
This mowing will help get sunlight down to the crown of the plant, drying the leaf blades as quickly as possible. This fungus like most fungi likes hot humid weather.
Minimize the amount you water as much as possible.
Wait until your lawn is getting a blue/green color and your foot prints stay in the lawn after you walk across it before you water. Unfortunately, you can not control rainfall as easily. In the Lowcountry, afternoon thunderstorms are a way of life, so keep the grass mowed as low as you can so it will dry out quickly.  
Hold off of the nitrogen fertilizer until you can get this disease under control.  If you need some color you could add a product like Possum’s Minors to give you some green without all the nitrogen.  
If you have to resort to a control product, make sure the product is labeled for Pyricularia grisea. There are many leaf spot diseases on labels of control products but only certain ones work on gray leaf spot on St. Augustine. We had one customer come in that had been applying a product that controlled Drechslera spp. and Biopolaris spp. leaf spot; however, the product was not labeled for Pyricularia grisea (watch where you shop). Honor Guard and Heritage are systemic products that you spray. Since this is a leaf spot fungus, the sprays seem to give good coverage over the leaf blade.  If you insist on a granular product, Prophesy (same active as Honor Guard and Banner), or Dual Action Plus Fungicide (same active as Heritage) are granular systemic products that will do a good job for you.
As the daylight hours decrease and the nights get cooler, watch out for Large Patch (Brown Patch) on all your turf (centipede, St. Augustine, Zoysia, and Bermuda). Preemerge your lawn and beds if you haven’t yet. If you have had Florida Betony in your beds in the past, this is the time to control it with Casaron before it comes up and is hard to spray because it is mixed in with you desirable plants. If we get a few overcast days, watch out for sod webworms or army worms hatching and munching on your turf.

Bill Lamson-Scribner can be reached during the week at Possum’s Landscape and Pest Control Supply, 481 Long Point Rd in Mt. Pleasant (971-9601), 3325 Business Circle in North Charleston (760-2600), or 606 Dupont Rd, in Charleston (766-1511).  Fax your questions to 406-2700 or e-mail them to your newspaper’s editors.
You can also call in your questions to “ The Garden Clinic”, Saturdays from 12-1 p.m. on 1250 WTMA  (The Big Talker).