Lawn Disease Reference
1) Snow Molds
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
Grass Type: 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.
2) Necrotic Ring Spot
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
Grass Type: 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.
3) 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.
4) Summer Patch
Occurrence: Summer
Favorable conditions: Hot, moist conditions; alkaline (i.e., high) soil and thatch pH
Grass Type: 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.
5) Dollar Spot
Occurrence: Summer
Favorable conditions: High humidity; low nitrogen fertility
Grass Type: 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.
6) Red Thread
Occurrence: Spring through fall
Favorable conditions: Wet, cool conditions
Grass Type: 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.
7) Rust
Occurrence: Summer and fall
Favorable conditions: High humidity, low soil moisture, low nitrogen fertility, shade
Grass Type: 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.
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