Comanche Extension Agent Michael Berry
Yellow San Augustine Grass
I do like the look and feel of San Augustine yard grass, but it can be hard to manage and seems to be more susceptible to disease and injury than most yard grasses. We have been getting a good many questions about yellowing in San Augustine grass and if you look around you will see many yards in the area that have some yellow San Augustine spots that may vary from small to large areas. What is causing the grass to turn yellow? Here are a few of the normal potential culprits in the case of the yellowing San Augustine leaves.
The first thing that comes to mind is a nutrient deficiency. Iron is commonly the cause of these paleyellow leaves. In high pH alkaline soils, iron chlorosis is common. This chlorosis is more common during the spring when the plants are growing rapidly but can occur anytime during the growing season. Plants that have iron chlorosis will normally have green parallel stripes in a predominantly yellow leaf. If the problem is iron chlorosis the application of a foliar iron product like Iron Plus, or a soil application of iron sulfide should do the trick.
A nitrogen deficiency would be the next potential reason for yellowing grass. With a nitrogen deficiency, the whole leaf will be solid yellow with the absence of green streaking. The addition of nitrogen should fix the problem. Many times, I find the iron and nitrogen deficiencies together within a yard. If this is the case, using a combination nitrogen and iron product should remedy the problem and turn your grass green. If you have recently fertilized with nitrogen, do not repeat in an effort to green-up your grass. If you have a fungus issue, the excess nitrogen will only make matters worse.
The worst-case scenario, and there are many yards already infested this year, is Take-All Root Rot (TARR). We have had lots of this in the county in previous years, and I think the abundant rainfall this spring and early summer may have made our San Augustine more susceptible to TARR this year. If you have yellow spots in your yard and areas of dead grass, this is likely your culprit. The areas of dead grass will continue to get larger. To determine if you have TARR check the stolon’s of your San Augustine- if you find short brown or black roots then you know you have TARR. If you have tried applying iron and nitrogen and you still have yellow grass, then you probably have TARR. The best treatment for TARR is to add sphagnum peat moss approximately 1” deep or 1 to 2 bales per 1000 square feet, over the infected areas. Give the peat moss an initial soaking then continue to irrigate and mow as you normally would. While maybe not overnight, the result of this treatment can be excellent.