When the thatch layer dries out during a drought, the root system becomes stressed. Excessive thatch can be removed mechanically. Using a core aeration machine to remove soil cores also provides better movement of water, air and nutrients into the soil. 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.
Fungicides can control many of the common diseases such as rust.
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. Rust, for example, usually doesn't reach damaging levels before the grass begins winter dormancy.