University of Wisconsin Garden Fact Sheets
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Lawn Disease Quick Reference

Authors: P.J. Liesch, UW-Madison Plant Pathology; Vijai Pandian, UW-Extension Brown County; and Jim Kerns, formerly of UW-Madison Plant Pathology
Last Revised: 01/02/2013
X-number: XHT1212

Snow Mold

Snow Molds
(Microdochium nivale and Typhula spp.)

Occurrence: Early to late spring

Favorable Conditions: Cold wet weather with periods of prolonged snow cover over unfrozen ground often leading to the most severe damage

Hosts: Kentucky bluegrass, tall fescue, perennial ryegrass

Symptoms: Circular, matted, gray to straw-colored patches ranging from a few inches to a foot or more in diameter

Management: Remove leaf litter from lawns. Mow lawns until dormant in the fall. Avoid heavy fertilizer applications (greater than 0.5 lb. N/1,000 sq. ft.) late in the year. Rake and lightly fertilize damaged areas in the spring to encourage recovery. Reseed lawns as needed.


Necrotic Ring Spot

Necrotic Ring Spot
(Ophiosphaerella korrae)

Occurrence: Spring, summer and fall

Favorable Conditions: Cool (soil temperatures of 55 to 65oF) and wet conditions for infection, followed by heat and drought stress for symptom development; most severe when soil compaction limits rooting

Host: Kentucky bluegrass

Symptoms: Circular, straw-colored patches usually less than 12 inches in diameter; regrowth often occurring in the center of patches, creating a “frog-eye” appearance; most common in newly sodded lawns, but also occurring in seeded lawns

Management: Reduce soil compaction and improve lawn drainage. Maintain proper fertility.  


Fairy Ring

Fairy Rings

(many mushroom-forming fungi)

Occurrence: Anytime

Favorable conditions: Warm, wet weather; significant thatch accumulation

Hosts: All cool-season lawn grasses

Symptoms: Type I: a ring or arc (up to several feet in diameter) of lush, dark green grass bordered by a band of dead turf, with or without mushrooms; Type II: a ring or arc of lush dark green grass with no band of dead turf, with or without mushrooms; Type III: a ring or arc of mushrooms with no band of lush green turf or dead turf

Management: Lightly fertilize and routinely core aerate lawns.


Summer Patch

Summer Patch

(Magnaporthe poae)

Occurrence: Summer

Favorable conditions: Hot, moist conditions; alkaline (i.e., high) soil and thatch pH

Hosts: Kentucky bluegrass, fine fescues

Symptoms: Ring-like patches of wilted turf up to 3 inches in diameter, similar to those of necrotic ring spot (see above), and with rings often merging into larger irregular patches

Management: Avoid excessive watering during hot periods. Core aerate to promote root growth and reduce compaction. Use acidifying fertilizers to lower thatch pH to below 6.5.


Dollar Spot

Dollar Spot

(Sclerotinia homoeocarpa)

Occurrence: Summer

Favorable conditions: High humidity; low nitrogen fertility

Hosts: Kentucky bluegrass, perennial ryegrass, fine fescues

Symptoms: Bleached patches ranging from a few inches to a foot in diameter, with leaf blades (inset) having bleached, hourglass-shaped areas

Management: Water deeply and infrequently early in the morning to minimize prolonged periods of leaf wetness. Apply nitrogen to alleviate symptoms.


Red Thread

Red Thread

(Laetisaria fuciformis)

Occurrence: Spring through fall

Favorable conditions: Wet, cool conditions

Hosts: Kentucky bluegrass, perennial ryegrass, fine fescues

Symptoms: Irregular beige patches ranging from a few inches to a few feet in diameter (oftentimes merging into irregular patterns) with red, thread-like filaments among the grass blades

Management: Collect clippings when disease is active. Maintain adequate nitrogen fertility.


Rust

Rust

(Puccinia spp., Uromyces spp.)

Occurrence: Summer and fall

Favorable conditions: High humidity, low soil moisture, low nitrogen fertility, shade

Hosts: Kentucky bluegrass, perennial ryegrass

Stand Symptoms: Reddish-brown, powdery areas (masses of fungal spores) that can discolor clothing and equipment

Management: Maximize light and airflow in lawns by pruning and thinning surrounding landscape plants. Water and lightly fertilize.

For more information on lawn diseases: See University of Wisconsin Garden Facts XHT1145, and XHT1150 (available at http://hort.uwex.edu), UW-Extension Bulletin A3187 (available at http://learningstore.uwex.edu), contact the UW-Madison Turfgrass Diagnostic Lab (see http://tdl.wisc.edu) or contact your county Extension agent.


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A complete inventory of University of Wisconsin Garden Facts is available at the University of Wisconsin-Extension Plant Disease Diagnostics Clinic website: http://pddc.wisc.edu.