Unraveling the Mystery of Large Patch Disease and Over-Irrigation St. Augustine Lawn In South Florida

Unraveling the Mystery of Large Patch Disease and Over-Irrigation on St. Augustine Lawn: A Comprehensive Guide to Lawn Recovery

A well-maintained, lush lawn can be a source of pride for homeowners in South Florida, enhancing the curb appeal and overall value of a property. However, unexpected problems can arise that may cause concern, such as large patch disease, which is often mistaken for grub infestation. This comprehensive guide delves into a real-life consultation in which a client believed their lawn had grubs, but upon closer inspection, the problem was diagnosed as large patch disease, combined with over-irrigation and excessive shade. We will discuss how to identify and treat large patch disease, address over-irrigation, and manage excessive shade to restore the lawn’s health and appearance. St. Augustine grass (Stenotaphrum secundatum) is a popular choice for lawns in South Florida, covering approximately 95% of all residential and commercial landscapes in the region. This warm-season turfgrass is well-suited to the area’s climate and soil conditions, providing a thick, lush, and attractive lawn. In this article, we’ll discuss the characteristics, advantages, and maintenance practices for St. Augustine grass that make it the dominant choice for South Florida lawns, however, it is subject to several lawn diseases including Large Patch Disease.

The Role of Low Temperatures in Large Patch Disease Development:

Low temperatures can contribute to the development of Large Patch Disease in several ways:
  1. Prolonged periods of leaf wetness: Cooler temperatures often lead to increased humidity and dew formation on the grass. This creates an environment with prolonged leaf wetness, which is favorable for the growth and spread of Rhizoctonia solani.
  2. Reduced grass growth: Low temperatures can slow down the growth of St. Augustine grass, making it more susceptible to infection. The reduced growth also means that the grass takes longer to recover from the damage caused by the disease.
  3. Weakened immune response: Cool temperatures can weaken the grass’s natural defenses, making it more susceptible to fungal infections like Rhizoctonia solani.

Section 1: Identifying Large Patch Disease

Large patch disease, caused by the fungus Rhizoctonia solani, typically affects warm-season turfgrasses and appears as discolored patches of grass that eventually grow and merge, causing widespread damage. The disease is influenced by temperature, particularly during cooler times of the year, when the fungus is most active.

1.1 Signs of Large Patch Disease

  • Circular, discolored patches ranging from a few inches to several feet in diameter
  • Yellowing or browning of grass blades within the affected area
  • Thinning or dying grass in the center of the patches
  • “Smoke rings” or dark, water-soaked borders around the patches during periods of high humidity
In our client’s case, the lawn showed no signs of grub infestation, as the grass could not be lifted easily, indicating that the roots were still intact.

Section 2: Contributing Factors to Large Patch Disease and Other Lawn Problems

Aside from temperature, several other factors may contribute to large patch disease and other lawn problems in South Florida, including over-irrigation, excessive shade, and improper mowing techniques. 2.1 Over-Irrigation Over-irrigation can lead to a variety of issues in a lawn, including weed infestation, shallow root growth, and increased susceptibility to pests and diseases. In the client’s case, over-irrigation was evident from the presence of numerous weeds throughout the lawn. 2.2 Excessive Shade Excessive shade created by surrounding trees or structures can prevent the grass from receiving adequate sunlight, limiting its ability to photosynthesize and produce essential nutrients for growth. In addition, shaded areas may retain more moisture than sunlit areas, creating a favorable environment for fungal diseases like large patch disease. 2.3 Improper Mowing Techniques Using a dull mower blade can cause tearing and damage to the grass, making it more susceptible to diseases and pests. In our client’s case, the lawn had been mowed with a dull blade, which led to an increased vulnerability to large patch disease. However, the lawn was mowed to the correct height of around three inches, which is a positive factor in maintaining a healthy lawn.

Section 3: Solutions for Large Patch Disease, Over-Irrigation, and Excessive Shade

To address these issues, a comprehensive plan was recommended, which involved a combination of treatment, irrigation adjustments, tree trimming, and proper mowing techniques. 3.1 Monthly Treatment Program A regular treatment program is necessary to prevent and control diseases like large patch disease, as they cannot be effectively treated reactively. By implementing a monthly treatment program that includes preventive fungicides, the lawn can be better protected from the spread of large patch disease. 3.2 Irrigation Adjustment Proper irrigation is crucial for maintaining a healthy lawn. Overwatering can lead to a variety of problems, including shallow root growth, weed infestations, and increased susceptibility to diseases. In the client’s case, reducing the
irrigation frequency to twice a week would help address the overwatering problem. In South Florida, daily watering may lead to water retention and promote weed growth. It’s essential to monitor local weather conditions and adjust the watering schedule accordingly. 3.3 Tree Trimming Pruning back trees to allow more sunlight into the area can help improve the lawn’s health and reduce the impact of excessive shade. Removing lower limbs, thinning out dense canopies, and selectively removing some trees can increase the amount of sunlight that reaches the grass, allowing it to grow stronger and healthier. 3.4 Proper Mowing Techniques Using a sharp mower blade is essential to prevent tearing and damage to the grass, which can make it more susceptible to diseases and pests. Regularly sharpening the mower blade and ensuring it is in good condition can significantly impact the overall health of the lawn. Additionally, it is crucial to maintain the appropriate mowing height for the specific grass type, as this can influence its ability to withstand stress and resist diseases. 3.5 Soil Aeration Aerating the soil can improve its overall structure, allowing water, air, and nutrients to penetrate more deeply and reach the grass roots. This process can help promote deeper root growth, making the lawn more resilient to drought and other stressors. Aeration should be performed at least once a year, ideally during the grass’s active growing season. 3.6 Proper Fertilization A well-balanced fertilizer program is essential for maintaining a healthy lawn. Applying slow-release, balanced fertilizers can provide the necessary nutrients for grass growth and help it recover from stress, such as large patch disease. However, it is crucial to avoid over-fertilizing, as this can exacerbate existing problems and lead to further damage. 3.7 Disease-Resistant Grass Varieties If large patch disease or other fungal diseases are a recurring issue in your area, consider planting disease-resistant grass varieties that may be more tolerant to such problems. Consult with a local lawn care professional or extension agent for recommendations on suitable grass types for your region.

How Can Over-Irrigation Contribute to Large Patch Disease in St. Augustine Lawns in South Florida?

Over-irrigation can lead to large patch disease in St. Augustine lawns in South Florida. To prevent this, it’s important to follow specific lawn care tips for St. Augustine grass. This includes avoiding excessive watering and ensuring that the grass has proper drainage to maintain its health and vitality.

Section 4: Monitoring and Ongoing Maintenance

To ensure the success of the recommended solutions, it is crucial to monitor the lawn’s progress regularly and make adjustments as needed. Regular maintenance and vigilance can help prevent recurring issues and ensure a lush, green lawn. 4.1 Monitoring Progress Regularly inspect the lawn for any signs of new or recurring problems. If large patch disease or other issues resurface, consult with a lawn care professional to determine the best course of action. 4.2 Ongoing Maintenance Consistent lawn care practices are essential for maintaining a healthy lawn. In addition to the solutions mentioned earlier, consider implementing the following ongoing maintenance tasks:
  • Dethatching: Remove excess thatch buildup, which can harbor disease-causing organisms and impede the flow of water and nutrients.
  • Overseeding: Reseed thin or bare areas to improve the lawn’s density and reduce the likelihood of weed and disease problems.
  • Pest Control: Monitor for pests and apply appropriate treatments as needed to prevent infestations and damage.
  • Proper Watering: Adjust the irrigation schedule based on weather conditions, grass type, and soil conditions to ensure the lawn receives adequate water without promoting disease.
Through a thorough consultation, the client’s lawn issues were accurately diagnosed as large patch disease, over-irrigation, and excessive shade, rather than grub infestation. By implementing the recommended solutions, such as adjusting the irrigation schedule, trimming trees, using a sharp mower blade, and maintaining a regular treatment program, the client can expect to see significant improvements in their lawn’s health and appearance. Regular maintenance and vigilance are essential to prevent recurring issues and ensure a beautiful, lush lawn for years to come.

Effective Fungicides for Large Patch Disease on St. Augustine Lawns in South Florida

Introduction: Large Patch Disease, caused by the fungus Rhizoctonia solani, is a prevalent turfgrass disease that affects St. Augustine lawns in South Florida. The disease presents as circular patches of yellow or brown grass, often expanding and merging into larger, irregularly-shaped areas. The disease can severely damage or even kill the affected grass. To manage and control Large Patch Disease, fungicides are often applied to prevent the spread of the fungus and encourage lawn recovery. Three common fungicides used to treat this disease include Propiconazole, Thiophanate-methyl, and Azoxystrobin.
  1. Propiconazole: Propiconazole is a systemic fungicide that belongs to the triazole group of chemicals. It works by inhibiting the biosynthesis of ergosterol, a crucial component of the fungal cell membrane, causing disruption of membrane integrity and ultimately leading to the death of the fungus.
Propiconazole is effective in controlling Large Patch Disease on St. Augustine lawns due to its ability to penetrate the plant tissues and provide long-lasting protection. The fungicide should be applied at the first sign of disease, and repeat applications may be necessary depending on the severity of the infection and weather conditions. The recommended application rate is 2-4 fl. oz. per 1,000 sq. ft., and it is advised to follow the label instructions for proper use.
  1. Thiophanate-methyl: Thiophanate-methyl is a systemic fungicide belonging to the benzimidazole group of chemicals. It works by inhibiting the process of cell division in the fungus, disrupting fungal growth and reproduction. This fungicide is effective against various lawn diseases, including Large Patch Disease in St. Augustine grass.
Thiophanate-methyl is typically applied as a preventive treatment, targeting the fungus before it has the chance to cause significant damage. The recommended application rate for Large Patch Disease control is 4-6 oz. per 1,000 sq. ft., with multiple applications spaced 14-21 days apart. It is essential to follow the label instructions to ensure proper application and efficacy.
  1. Azoxystrobin: Azoxystrobin is a broad-spectrum, systemic fungicide that belongs to the strobilurin group of chemicals. It functions by inhibiting the process of mitochondrial respiration in the fungus, leading to energy depletion and eventually cell death.
Azoxystrobin is highly effective against Large Patch Disease and can be used as both a preventive and curative treatment. When used as a preventive treatment, it is typically applied before the onset of favorable conditions for disease development. For curative treatment, it should be applied as soon as the disease symptoms are observed. The recommended application rate is 0.5-1.0 fl. oz. per 1,000 sq. ft., and repeat applications may be needed depending on the severity of the infection. Always follow the label instructions for proper application and optimal results. Large Patch Disease can be a devastating problem for St. Augustine lawns in South Florida. The use of fungicides such as Propiconazole, Thiophanate-methyl, and Azoxystrobin can effectively manage and control the disease, preventing its spread and minimizing damage. It is crucial to apply the fungicides according to their label instructions and recommended application rates to ensure their efficacy and protect the health of your lawn. Don’t let large patch disease, over-irrigation, and excessive shade ruin your beautiful lawn. Take action now to restore your lawn’s health and maintain its lush, green appearance. Consult with a professional lawn care expert today to develop a tailored plan that addresses your lawn’s unique challenges. Don’t wait any longer; your lawn deserves the best care possible. Contact us now and let our team of experts help you transform your lawn into a thriving, stunning outdoor space that you can be proud of. Act now and experience the difference that expert lawn care can make!

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