Answer: The main disease affecting St. Augustine grass is Take-All Root Rot. This disease is active in the fall and spring when the soil temperatures are in the 60- to 65-degree range. At this time of the year, the fungi attacks the plant's root system, weakening it as it goes into the winter and summer stress periods. This disease appears to be particularly active on plants that have been become stressed for one reason or the other.
Roots of these affected plants are usually short, blackened and rotted, and the stolons (runners) can easily be lifted from the soil due to the poor root system. As the disease progresses, the yellow leaf blades will eventually turn brown.
Take-All Root Rot can often be mistaken for Brown patch. These two diseases can be distinguished by pulling on the leaf blades of the yellow to brown leaves. Leaves of Take-All Root Rot plants are still firmly attached to the stolons, while leaves with Brown patch can easily be pulled away from the stolons. Also, Brown patch rarely causes the roots to turn black.
The best time to treat for Take-All Root Rot is in the fall and spring when the soil temperatures are in the 60- to 65-degree temperature range. While controlcan be difficult, fungicides such as Heritage, Rubigan and BannerMaxx have shown some control for this particular problem.
Proper irrigation during the summer months and particularly fall months will aid in preventing Brown patch activity. Also, avoid excess applications of nitrogen fertilizers during the summer months and especially in the fall months when night temperatures drop below 70.
Good luck with your lawn!
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