Every summer, it seems, our fescue lawns suffer with a multitude of ugly brown areas.  Often, the areas start small, multiply, and by the end of the summer, have taken over the entire lawn.  Most often, the brown areas are associated with some type of fungus that caused disease.

Rhizoctonia damping-off, blight and rot
Rhizoctonia solani
– Ward Upham, Kansas State University, Bugwood.org

Several diseases affect our fescue lawns but one in particular is typically quite prevalent every year.  Rhizoctonia blight (or Brown Patch for short) is a common infectious disease of turf and can be very destructive on fescue and perennial ryegrass.  Areas affected by brown patch are initially circular, varying in size from 1-5 feet.  If you look early in the morning, fine strands of grayish cobwebby fungal growth (mycelium) can be seen at the margin of the circular areas.  As the disease progresses, circular patches coalesce and form irregular shaped patches.

The individual blades of grass show detailed symptoms.  They will have olive green lesions that dry quickly during the day and turn tan with a darker brown border; eventually taking over the entire blade of grass.

Brown Patch is caused by Rhizoctonia, a very common soil born fungus.  Rhizoctonia survive the winter as tiny brown sclerotia in the soil and thatch layer of the lawn.  When environmental conditions are right, they germinate and start producing the mycelium that attack the plant.  Typically, Rhizoctonia mycelium will not cause much damage on healthy turf but when the plant is stressed, it can quickly become a problem.  Fescue is a cool season grass and does not perform well in high temperatures and high humidity.  Rhizoctonia, however, loves high temps and high humidity.

To manage brown patch, we need to make sure we give the turf the best defenses first.  Make sure when selecting turf varieties, you look for built in resistance to brown patch.  There are many varieties of turf type tall fescue out there and many of them offer some degree of resistance.  Ky 31 is not a good choice for most home lawns because when mowed regularly, Ky31 have little if any resistance.

Application of nitrogen fertilizer in the spring and summer favors development of brown patch by producing lush, succulent growth that is extremely vulnerable to brown patch.  Reduce fertilizer applications in the spring and summer.  Instead, apply nitrogen in the fall and early winter.

We all like super green, thick, lush grass but the thicker your lawn is, the less air movement you have in between the blades.  Less air movement equates to more moisture for longer periods of time.  Rhizoctonia loves that environment and quickly spreads throughout your lawn.  Make sure to adhere to proper seeding rates when establishing or renovating your lawn.

Other factors increase disease severity by creating a humid environment favorable to Rhizoctonia.  Watering in late afternoon or evening creates a very moist environment that lasts all night; plenty of time for the fungus to attack.  Poor soil drainage, mowing when wet, and dull mower blades all contribute and enhance disease severity.

In established lawns, fungicide sprays are not recommended to control brown patch because  the aforementioned cultural practices typically keep brown patch under control.  Even if an outbreak occurs, crowns and roots of established plants will survive and recover as soon as temperatures cool down in September.

For newly planted lawns, often a fungicide is recommended.  During the summer, following a spring seeding, the immature plants can be easily killed by brown patch and a fungicide application will likely prevent plant death.  There are several fungicides available locally both in granular form or liquid concentrate.  Make sure to follow the label and apply all pest products properly for best control and to protect the environment.

If you have suspected disease in your lawn, make sure you properly identify the disease first and then look at your cultural practices.  Most of the time, we can strengthen the plant to withstand the stress of the summer heat and humidity.  If you have questions about your lawn, give your local Extension office a call; we are happy to help!

Submitted by Andrew Rideout, Agent for Horticulture, Henderson Co. Cooperative Extension Service