In some cases, extended drought can severely injure or kill tall fescue. If you choose to irrigate, do it efficiently. Walk across your lawn. If your footprints remain in the grass very long, the lawn is dry. When a lawn is dry a long time, it will exhibit a bluish-gray cast.
Dry grass responds by wilting and rolling or folding the leaves.
If the soil is very dry, it will be hard to insert a screwdriver into the lawn. If any of these techniques determine your lawn is dry, apply about an inch of water. If runoff is a problem, apply half and let it soak in. Then apply more. Early morning is the best time to water.