Diseases can be quite selective. A mixture of grasses will prevent complete destruction of your lawn. TEST YOUR SOIL . Send to the Dept. of Agriculture, Plant Industry Branch, P. O. Box 550, Truro, N. S. B2N 5E3 for a soil test kit. Such a test will give your soil's pH, organic matter content and nutrients needed to balance it.
Organic matter increases nutrient-holding capacity and improves aeration and water retention.
Thatch chokes out grass plants, prevents air, water and nutrients from reaching the soil, and promotes almost every possible lawn problem. Aeration and a brisk raking should remove much of the thatch. This encourages deeper rooting and allows water, nutrients and organic matter to feed the soil. Earthworms are terrific aerators. Lots of worm holes in the lawn mean the job is being done for you.