Summer lawn diseases are sometimes hard to properly identify because of the similarities between the diseases.  Some of the lawn diseases actively present in the summer produce similar damage to that of drought stressed grass.  Through grass-blade examination and taking in to consideration weather conditions, one can narrow down the fungus candidates and make a proper identification.  Some of the most common summer fungus present in Kentucky bluegrass are brown patch, pythium blight, summer patch, smut and rust.  Below is a quick review on the characteristics and the preferred climate conditions of each of the lawn diseases.

Common lawn diseases.

Brown Patch

Yellow lesions with brown rings form on the grass blades.  This fungus prefers warm temperatures above 65 degrees F that remain at or above this temperature throughout the night.  Rainy, humid weather promotes the spread of this fungus.

Pythium Blight

Circular, bluish to brown patches will appear in small areas, rapidly increasing in size.  Creamy white fungal threads form on the blades of the grass, almost resembling that of cotton.  High temperatures above 90 degrees F and heavy humidity above 90% are the perfect conditions to promote the development of pythium blight.

Summer Patch

Circular patches that are light to dark tan in color slowly form by wilting turf grass.  Temperatures over 85 degrees F during the day and over 60 degrees F at night help this fungus thrive with active rain conditions.  This fungus can become extremely harsh during hot, wet years with poorly drained soil.


Smut forms in long yellow and black streaks on grass blades.  This disease occurs during temperatures above and around 50 degrees F with above average rainfall.  This disease can cause severe damage to older established turf. 


Orange powder almost like dust forms on grass blades infected with rust.  Rust  is easy to spot, because you will notice this fungus when you walk through your lawn and the orange pustules stick to your shoes.  This fungus favors warm nights over 70 degrees F and is usually seen in shady areas.

Treatment for most lawn fungus is throught the use of a fungucide.