Q. I have irregular brownish patches that appeared in my lawn in the backyard about 2 weeks ago. Can you tell me what is going on?
A. This year is a complete opposite of the hot dry conditions we experienced last year in northeastern Indiana. Some areas are 7.5 inches above normal precipitation for the year. Whenever there is wet weather, there are fungal diseases galore.
Pythium blight is a warm-weather disease of cool season grasses. The disease is most destructive during hot humid periods when temperatures are between 85 degrees and 95 degrees during the day, with average evening temperatures of 68 degrees or higher.
Outbreaks will typically first appear in low areas, or poorly drained areas where soil moisture is maintained. Pythium blight is characterized by circular reddish brown spots in the turf. In the morning dew, infected leaf blades appear water soaked and dark and may feel slimy.
When spots are wet with dew, purplish gray or white cottony fungal mycelia can be seen on the outer margins of the spots. Large areas of turf can be lost in a short period of time. Pythium blight appears more frequently in lawns over managed by the use of high nitrogen fertilizer and irrigation.
Brown patch is another summer lawn disease that appears during hot humid weather. The infected leaves first appear water soaked and dark, eventually drying, withering, and turning dark brown. A dark smoke ring often surrounds the outer margins of the diseased area when humidity is high and disease is actively growing. Leaves in the blighted area are usually killed, and the disease can also rapidly kill large areas of turf grass in short periods of time.
Melting out disease often appears during cool wet conditions; something we have seen frequently this year.
Symptoms first appear as black to purple spots on the leaf blades. The fungus may eventually invade the crowns and roots of the grass plant. If cool, wet conditions persist, the crown and root rot stage of the disease follows, and infected turf grass begins to thin and die.
Rust diseases are also prevalent in our area. The spores of rust are blown in from the south during storms – usually in late summer. When rust is severe, areas of infected turf appear thin and have a red, brown, or yellow tint. After mowing the lawn, one will notice red dust over shoes. Heavily infected plants – especially on new stands of turf – may wither or die from excessive loss of moisture from rusted leaves.
It is better to immediately consult with a lawn care professional if one suspects a summer lawn disease – especially if the damage progresses rapidly.
The exception is rust, which usually can be controlled with a fertilizer application. These summer diseases can be quite serious and shouldn’t be taken lightly.