Crisp autumn air is a welcome relief — unless you’ve been overwatering your lawn. Cooler temperatures and increased moisture make your grass susceptible to fungal disease.

Cooler temperatures and increased rainfall multiply the chances of disease problems in local lawns. Bermuda, zoysia and St. Augustine grasses can be susceptible to fungal diseases if the following conditions are present: overwatering or high soil moisture, high levels of nitrogen, high soil pH, or improper mowing height.

Here are the common fungal turf diseases in San Antonio.

Take-all root rot (pdf) or take-all patch, is a very common fungal disease in St. Augustine characterized by yellowing of the grass and tiny puzzle piece-shaped fungal structures called hyphopodia on the stolons. Reducing water application where possible and applying sphagnum peat moss or ammonium sulfate fertilizer to the lawn helps reduce pH in the soil. Fungicide products should be applied before this fungus becomes a problem because it’s very difficult to cure once established.

Brown patch fungus, or Rhizoctonia, is another disease that appears when nighttime temperatures drop below 68 degrees and daytime temps stay in the mid-80s, combined with extended periods of increased humidity. Avoid applying too much nitrogen fertilizer and reduce thatch levels in the grass to help reduce moisture. Infected grass blades can be easily pulled off of the stolons. There are many fungicide products available on the market that will stop this fungus when applied properly.

Gray leaf spot fungus effects St. Augustine grass in late summer as the result of high humidity and proper conditions. The leaf spots are grayish in color with purple margins. Grass infected with this fungus should not be given nitrogen fertilizers until the disease is cured. There are products available to help treat this disease.

Fungal diseases are usually the result of high moisture and humidity combined with cooler temperatures. Reducing the amount of water applied to the lawn, utilizing core aeration to reduce compaction and proper fertilization of the soil can help you reduce the chances of fungal diseases in your turf.

For green healthy lawns, remember that “Less is best.” Less water, less fertilizer and less compaction.

By Nathan Riggs,   SAWS Project Coordinator and Licensed Irrigator who also happens to have a degree in entomology from Texas A&M University. Yes, Nathan’s a bug expert, and not just on water bugs! When he’s not hard at work on SAWS conservation projects, he enjoys a wide variety of interests including: landscaping, hiking, photography of flowers, insects and other critters, and planning his next adventure with his wife Ella and family.