Powdery mildew, one of several fungal diseases that infects the blades of grass, leaves a white powder-like patch on your lawn. It usually occurs on cool-season grass, such as Kentucky bluegrass, which is most susceptible, as well as Bermudagrass, and all the grass fescues.
The first signs of this mildew damage are light patches of dusty white
or light gray growth on the grass blades. The lowest leaves can get
This mildew fungus, technically known as Erysiphe graminis, infects the surface of the grass blades, where it develops a fine, fungal growth that looks like white powder or even a dusting of lime or flour.
In areas that have been hit harder by the disease, it can actually look like it's been sprayed with a coat of white paint.
You're most likely going to find this lawn mildew in the late spring and summer, and then again in fall. It will survive over the winter in the dead grass from the previous season.
It likes high humidity and thrives when temperatures are 60F - 70F in those areas where air circulation is rather poor.
As is typical to most fungus growth, it will be found to be more severe in the densely shaded areas of your lawn. It appears quite suddenly, so don't be surprised if you've walked the lawn a few hours earlier and haven't noticed it then.
Research shows that it will usually appear on Kentucky Bluegrass and fescues.
Here are some practical management suggestions to follow.
It's a good idea to reduce shade and increase the air circulation. A good way to do this is to prune nearby shrubs and trees.
If your grass is weak and not growing well in those shady areas, why not consider replacing it with a shade-tolerant ground cover.
Practice proper mowing techniques and be sure to raise the mower cutting height. You should never cut more than 1/3 of the grass blade.
Avoid the use of fertilizers that are high in nitrogen if possible, and practice proper water techniques by watering infrequently but deeply.