Warm wet grass, for more than a few hours at a time, in poorly drained soil promotes many lawn diseases by activating fungus spores. Conversely, some lawn trees are moisture robbers and grass growing in their root zones may need additional watering. Mow at the proper height for your lawn grass variety. As a general rule, the chances for disease damage are increased as the height of mowing is decreased. Mowing with a sharp mower blade on a more frequent schedule will produce a healthier lawn.
Spores can also accumulate on mowers and other equipment and then are spread to healthy plants.
This is most likely to occur when wet grass is mowed. Clean the mower blades after use with a soft spray of water. Forceful cleaning can push dirt into delicate bearings. Do not spray water onto a hot engine. Check thatch and remove if necessary in Fall or Spring.