A dear friend of our family, Mark, loves to mow and care for his lawn. This past week, he sent me pictures of yellowing patches in various areas of his lawn. He said they are not necessarily in circles, but the tops turned yellow. When he rakes the area, the blades of grass come up as though they are rotten while the roots remain intact.
Is this normal? It can be and, oddly enough, is more common in pampered lawns rather than in those who are not.
Fall weather patters of cooling temperatures and heavy dews find many East Texas homeowners noticing irregular patches of yellow or brown grass that seem to expand overnight. At this time of year, fungal diseases are often the culprit, and two in particular—brown patch and take-all root rot—cause the most concern in our area.
Researchers with Texas A&M AgriLife Extension explain that fungi thrive when soil temperatures fall below 80°F and moisture lingers. September and October often provide exactly those conditions: warm days, cool nights, and frequent rainfall or dew. If your lawn is made up of St. Augustine grass, zoysia grass, or even bermudagrass in shady areas, the environment is perfect for fungal outbreaks.
Our part of the world loves St. Augustine grass, has plenty of trees to provide some shade, and the weather is in the perfect condition – all leading up to problems in too many lawns.
The disease most homeowners, including Mark, encounter is brown patch, caused by the fungus Rhizoctonia solani. Symptoms include circular or irregular patches of yellowing turf, ranging from a few inches to several feet across. Studying the area further, you can find individual blades with rotted areas near the leaf base. Lastly, the grass can be pulled easily from stolons (runners) because the tissue at the crown has rotted.
Some good news is that brown patch is primarily a leaf and crown disease and does not usually kill the entire root system, so turf often recovers when conditions dry. Still, repeated infections weaken the lawn, leaving it thin going into winter.
The second major disease, take-all root rot (Gaeumannomyces graminis), can also show up in the fall but often becomes visible in spring after cool-season stresses. Unlike brown patch, take-all is a root disease, leaving grass yellow, stunted, and prone to death in patches that do not recover easily. St. Augustine grass is especially vulnerable, but all types may be susceptible.
Research from several universities highlight more than a few cultural practices that make fungal problems worse. Top of the list is late-season nitrogen fertilization. High nitrogen in September encourages lush, tender growth that fungi readily attack. While “winter-izer fertilizer” can be a good thing, too much and you will be setting your lawn up for problems.
Next is excessive irrigation coupled with poor drainage. Watering when it gets dry is a smart practice. However, watering late in the day, worst yet in the evening, will leave water standing overnight, keeping leaves wet, and absolutely fuels fungal growth.
Dense shade and poor air circulation are another contributing factor. We love our trees in East Texas and are blessed to have them. Yet lawns in tree-heavy areas stay damp longer, providing ideal conditions.
Heavy thatch buildup. Thatch is the dense layer of dead and living shoots, stems, roots, and other organic matter that builds up between the grass blades and the soil surface. Though completely organic, it holds moisture at the crown of the grass and harbors fungal spores.
While all these factors work against you, there is still plenty you can do. The best management strategies are preventive, not reactive. AgriLife turfgrass specialists recommend adjusting fertilizer timing. Skip heavy nitrogen applications after early September. Instead, if your soil test calls for it, apply potassium (0-0-60) to strengthen your turf for winter.
Water wisely. Irrigate deeply but infrequently, and always in the morning so leaves dry quickly. An overly simplified rule of thumb is to ensure that your lawn gets one inch of water per week. If you get one or more inches of rain, then no need to irrigate.
And when you do water, water only in the morning and, if possible, only two days each week.
Mow at the right height. Keep St. Augustine at 3–4 inches to reduce stress and never remove more than one-third of the blade at once. This 3-4 inch height is certainly much higher than most folks like, but taller blades of grass encourage deeper roots and will reduce water stress.
Reduce shade if practical and thatch if possible. Prune trees for better air flow and dethatch if buildup exceeds ½ inch.
Consider fungicides when needed. If your lawn has a history of severe brown patch and weather forecasts predict prolonged cool, wet conditions, preventive fungicide applications may be justified. Fungicides are most effective when applied at the very first signs of disease, not after large areas are already damaged. Products with active ingredients such as azoxystrobin, propiconazole, or myclobutanil are commonly recommended, but always follow label directions carefully.
I love fall and my friend Mark loves tending his lawn. But while fall is a wonderful season in East Texas, it’s also the prime time for fungal diseases to appear in lawns. Knowing what to look for and managing your turf wisely can make the difference between a green lawn in spring and one struggling to recover.
