Diseases in turfgrass can occur, especially in lawns with grass species that have moderate to low tolerance to heat and/or drought and, therefore, have suffered through the hot and dry spell.
Turf diseases are tied to the type of grass planted (bluegrass, fescue, etc.), the plant health, soil nutrient status, soil drainage, watering practices, and stressors such as temperature, compaction, and drought.
Water Deeply in the Morning
If you decide to water your lawn, an early morning application is preferred as opposed to evening irrigation. Avoid night watering. This increases the length of time grass blades remain wet. Many fungi need to be wet for a certain period of time to infect grass blades. Early morning or afternoon irrigation ensures that plants dry by evening.
Avoid light applications of water; instead, water deeply but infrequently. Uniformity of coverage is important to avoid neglecting areas.
Learn more in this article: Watering Tips for the Garden, Lawn, and Landscape.
Mow Frequently at a High Height
Mow when the grass is dry. Set the mowing height on your mower higher (2.75 to 3.5 inches). Mowing below recommended heights depletes the grass of energy reserves, thins the lawn's canopy, and encourages weeds. The best strategy is to mow frequently, but never remove more than one-third of the plant height.
Reduce stress on the turf by removing no more than 1/3 of the leaf blade at one time.
Learn more in this publication: Mowing Your Lawn (PDF).
Follow a Balanced Fertilizer Program
When too much or too little fertilizer is applied, diseases can thrive. Certain diseases, such as rust and dollar spot, tend to occur more on nutrient-deficient lawns. Excessive fertilization favors leaf growth at the expense of root growth, making the lawn susceptible to other diseases such as summer patch, brown patch, or Pythium blight. In general, spring and fall applications of a slow-release form of nitrogen are recommended.
Learn more in this publication: Lawn Fertilization (PDF).
Improve Air Circulation and Light Penetration
Several diseases are more severe in shady areas. Additionally, areas that see little air movement are more likely to stay wetter longer, promoting disease. If possible, limb up trees and prune back shrubs to allow for better light penetration and air circulation. In areas that are not receiving full sun, consider growing something other than turf.
Learn more in this article: Growing Grass in Shady Areas.
Avoid Excessive Thatch
A moderate thatch layer no more than 1/2 inch thick is beneficial, acting as a protective mulch layer. When thatch becomes excessive, the roots of grass plants tend to grow in the thatch layer rather than in the soil. When the thatch layer dries out during a drought, the root system becomes stressed.
Most residential lawns do not have excessive thatch layers, especially when regular core aeration is done (and core aeration has benefits beyond controlling thatch!). However, on highly maintained turf, thatch can become an issue. Remove excessive thatch if the layer is more than 1/2 inch thick.
Learn more in this article: What is thatch?
Correct Drainage
If drainage is problematic on your lawn, take the necessary steps to improve drainage to promote water percolation while helping minimize leaf wetness. Learn more in this article: Testing and Improving Soil Drainage.
Grow Disease-Resistant Cultivars
Many grass cultivars possess resistance to certain diseases. It's a good idea to include one or more disease-resistant cultivars in a blend when seeding. Existing turf that has frequent issues can be interseeded with disease-resistant cultivars.
Fungicides Have Limited Effectiveness in Home Lawns
Fungicides can control many of the common diseases. These products, however, cannot replace good cultural practices that reduce stress to lawns.
Effectiveness depends on the correct diagnosis of the problem and proper timing of applications. Most products need to be applied before the disease shows up or at the very first signs of disease. It's sometimes difficult to determine whether fungicide sprays are warranted. Many diseases, such as rust or powdery mildew, usually don't reach damaging levels before conditions improve, or the grass begins winter dormancy. Fungicides are not routinely used.
Submit a Sample
If problems arise, the Plant and Insect Diagnostic Clinic can assist you in investigating what the problem may be and how to manage it.
Proper samples are essential to good diagnosis. When collecting a turfgrass sample, collect samples before applying any fungicides and collect turfgrass from the edge of the affected area. The sample should include both healthy and infected plants. Completely dead grass is of no use since secondary organisms quickly colonize it. Take a sample of at least 6" diameter (a cup cutter works well). Include the underlying soil and root system.
Wrap the sample in newspaper or paper towels. Please do not place it in a plastic bag, and do not add water. Excess moisture can cause rapid deterioration of the sample and proliferation of secondary organisms. Provide background information, such as when the symptom first appeared, turfgrass variety, and pattern and distribution of the problem. Along with the sample, pictures of symptoms can be very helpful. Pack and wrap the sample tightly in a box to prevent dislodging the soil. Ship the package early in the week via overnight delivery when possible.
Learn more about submitting a sample in this article: How to Submit a Sample.