What is brown patch?
Brown patch is a common lawn disease that affects cool-season grasses such as tall fescue, perennial ryegrass, and Kentucky bluegrass. It is caused by the fungus Rhizoctonia solani and thrives in warm, humid conditions. Brown patch gets its name from the circular brown patches it creates in the turfgrass. The blades of grass in affected areas die quickly, creating sunken patches of thin, brown grass.
Brown patch is most active when nighttime temperatures are above 60°F and daytime temperatures are between 75-90°F. Extended periods of leaf wetness from rain, irrigation, or high humidity encourage the spread of the fungus. Brown patch may subside during hot, dry weather but the fungus remains present in the soil and thatch layer waiting for favorable conditions to return.
What does brown patch look like?
The earliest symptoms of brown patch are small, dark brown or black spots that develop on grass blades. The spots enlarge rapidly and turn light brown or straw-colored. Within days, roughly circular patches of thin, blighted turf appear. The patches range in size from a few inches to several feet across. Affected areas feel soft, mat-down easily, and pull up easily from the soil. Often there is a smoke ring or dark brown border along the outer edge of the patch.
During prolonged favorable conditions, brown patch patches may merge into large irregular dead areas. When temperatures rise and conditions dry out, the grass within the patches dies quickly and turns straw brown. A red-brown waxy coating may develop on the crowns and roots of affected plants.
Brown patch damage is most prevalent in areas of turf that are stressed by traffic, poor drainage, or inadequate fertilization and cultivation practices. Damage often appears first and is most severe in low wet spots or on compacted soils.
How does brown patch develop?
The brown patch fungus (R. solani) survives the winter in plant debris and thatch. In spring the fungus becomes active again, producing spores that can be spread by splashing water, wind, and mowers. Under warm, humid conditions, spores germinate and infect the grass blades. The fungus spreads rapidly from leaf to leaf when temperatures are above 60°F and leaf surfaces remain wet for long periods.
Once inside the plant, the fungus produces toxins that kill the grass tissue. It also causes a substantial loss of water and nutrients from the plant. Affected plants quickly turn brown and die. The fungus continues growing on the dead tissue, allowing further spread.
Outbreaks are most common in lawns that are heavily fertilized with nitrogen, especially in spring and early summer. Excess nitrogen creates succulent grass growth that is highly susceptible to infection. Irrigating in the late evening or at night can also promote brown patch by extending the period of leaf wetness.
How can I prevent brown patch?
While brown patch cannot be completely eliminated, the following cultural practices can greatly reduce the severity of outbreaks:
– Avoid excessive nitrogen fertilization which produces soft, lush growth. Do not apply more than 1 lb nitrogen per 1000 sq ft per application.
– Irrigate early in the morning, not at night. Allow turf to dry completely before nightfall.
– Improve drainage in low spots and reduce compaction. Aerify as needed.
– Promote good air circulation around plants through proper spacing and pruning.
– Raise mowing height in summer to encourage deeper rooting. Never remove more than 1/3 of the grass blade when mowing.
– Remove dew and guttation water by dragging hoses or special absorbent materials over the lawn in the early morning.
– Reduce thatch through aerification, dethatching, or topdressing. Thick thatch retain moisture and humdity.
– During outbreaks, avoid overhead irrigation and mowing diseased areas to reduce spread.
How is brown patch treated?
At the first sign of brown patch, apply a fungicide containing one of the following active ingredients:
– Azoxystrobin
– Myclobutanil
– Propiconazole
– Pyraclostrobin
Make additional applications at 7-14 day intervals if conditions remain favorable for disease development. Always follow label directions carefully when applying any fungicide.
In addition to fungicide applications:
– Remove dew and guttation water from plants in the early morning.
– Avoid irrigation in the late evening and at night.
– Reduce fertilizer applications and avoid excessive nitrogen.
– Mow diseased areas last to avoid spread. Clean mowers thoroughly after use on affected lawns.
– Aerify and improve drainage in affected areas.
With prompt treatment and favorable weather, turf in affected areas can recover in 10-14 days. Damaged turf may need to be reseeded in fall.
Key facts about brown patch
Causal agent
– Rhizoctonia solani, a soil-borne fungus
Primary hosts
– Cool-season grasses: tall fescue, perennial ryegrass, Kentucky bluegrass
Conditions for development
– Night temps above 60°F
– Day temps 75-90°F
– High humidity
– Extended leaf wetness
Symptoms
– Small dark spots on grass blades
– Circular brown patches 6 inches to 3 feet across
– Straw-colored, matted grass in patches
– Reddish-brown blighted rings or smoke rings around patches
– Dieback and thinning turf
Treatment
– Azoxystrobin, myclobutanil, propiconazole, or pyraclostrobin fungicides
– Avoid excess nitrogen fertilization
– Improve air circulation and drainage
– Water early in day, allow turf to dry before nightfall
Prevention
– Moderate nitrogen fertilization
– Morning irrigation
– Reduce thatch
– Aerify compacted areas
– Raise mowing height in summer
Will brown patch harm other plants?
Brown patch is a very host-specific disease and only affects certain cool-season lawn grasses. The fungus Rhizoctonia solani does not infect warm-season turfgrasses, landscape plants, or garden plants. So brown patch will not spread from an affected lawn into flower beds, gardens, or ornamental plantings. The disease stays confined to the susceptible lawn grass.
However, Rhizoctonia solani is a species complex with many different strains. Some strains do attack specific warm-season grasses, while other strains cause various blights, root rots, and damping-off diseases on a wide range of hosts. But the strains that incite brown patch are only infectious to cool-season turfgrasses. So neighboring landscape plants are not at risk from a brown patch outbreak in the lawn.
Does brown patch indicate poor soil health?
Brown patch outbreaks are influenced more by environmental conditions and cultural practices than soil health. But certain aspects of poor soil can predispose turfgrass to more severe cases of brown patch:
Compaction
Heavily compacted soils restrict root growth, reduce drainage, and limit air exchange around grass plants. Compaction creates physiological stress making the turf more vulnerable to opportunistic brown patch infections. Aerifying to alleviate compaction can promote healthier roots and reduce brown patch severity.
Nutrient imbalances
Excess nitrogen from fertilizers produces soft, succulent grass growth that is highly susceptible to foliar diseases like brown patch. Insufficient levels of manganese, potassium, and other nutrients may also weaken turfgrass and encourage disease. Maintaining proper soil nutrient balances enhances overall turf health.
Poor drainage
Standing water and soggy conditions allow fungal pathogens like Rhizoctonia solani to thrive. Improving drainage through grading, aerification, or amendments reduces saturated soils around grass roots. Drier soils are less congenial to brown patch development.
Thatch buildup
An excessive thatch layer retains excess moisture and humidity within the turfgrass canopy which favors brown patch fungal activity. Thatch also limits contact between roots and soil. Reducing thatch through dethatching, aerating, or topdressing can diminish brown patch pressure.
So while brown patch itself does not necessarily indicate poor soil health, addressing issues like compaction, drainage, and nutrient deficiencies through improved soil management provides stronger turfgrass with better resistance against disease problems.
What are other common lawn diseases?
In addition to brown patch, some other common fungal diseases of lawns include:
Dollar spot – Small round spots or patches of bleached, straw-colored grass. Affected areas turn reddish-brown. Mainly attacks bentgrass and Kentucky bluegrass. Aggravated by inadequate nitrogen.
Gray leaf spot – Tiny brown-centered lesions on grass blades which turn into long gray or tan streaks. Most severe on perennial ryegrass and St. Augustinegrass. Worsened by high nitrogen and humidity.
Red thread – Pinkish-red threadlike growth on grass leaves. Blades later turn brown in roughly circular patches. Primarily affects fescue and bluegrass. More prevalent in acid soils.
Rust – Yellow, orange, brown or black blister-like pustules on blades. Severe infections kill leaves. Mainly impacts bluegrass, fescue and ryegrass. More common in shady, damp sites.
Pythium blight – Rapid blighting and collapse of new grass growth. Leaves develop a greasy or water-soaked appearance. Most problematic on newly seeded lawns. Aggravated by excessive moisture and high temps.
Take-all root rot – Overall yellowing and reduced density of turf. Blackened roots and stolons. Most severe on bentgrass golf greens. Worsened by acidic soils.
Proper mowing, irrigation, fertilization and thatch management practices can help minimize infection by these common lawn diseases. Targeted fungicide applications may be needed in some cases to achieve control.
How long does brown patch last?
The duration of a brown patch outbreak largely depends on the weather and how favorable conditions remain for disease development. Under optimal warm, humid conditions, brown patch can spread rapidly and cause extensive blighting of turfgrass within 7-10 days. But hot, dry weather will halt further spread and allow turf to recover.
Brown patch is most active when nighttime temps are over 60°F coupled with daytime highs of 75-90°F. Prolonged leaf wetness from rain, dew or irrigation also encourages fungal growth and disease spread. So the disease progresses fastest under these ideal conditions for the pathogen.
Once daytime highs exceed 90°F and/or the turf is allowed to dry out thoroughly, brown patch will become suppressed. Turf in affected areas often recovers within 10-14 days given cooler, drier weather or manageable irrigation schedules.
However, the brown patch fungus does not completely disappear. It persists in the soil and thatch ready to resume growth when conditions become favorable again. So additional outbreaks may develop periodically throughout the summer, especially on susceptible turfgrass that is heavily fertilized and irrigated.
Does brown patch go away on its own?
In many cases, brown patch will eventually resolve on its own without any treatment. As temperatures rise and weather turns hot and dry, conditions become less ideal for continued fungal growth. The disease essentially runs its course.
The turfgrass plants also mount natural defense responses to the infection that help restrict pathogen invasion and damage. Their production of antifungal compounds and rapid cell growth slows further colonization.
Additionally, mowing and foot traffic help remove browned blades infected with spores. This diminishes the potential inoculum available for new infections.
So given enough time, hot and dry conditions, and the turf’s own defenses, an outbreak of brown patch will often decline and affected areas will fill back in on their own through growth of new blades. Natural processes bring about a gradual resolution.
However, damage may be extensive and recovery prolonged without intervention. Fungicide applications, improved cultural practices, and proper supporting care will quicken turfgrass regrowth and restore density faster. Relying solely on natural processes could mean a thin, weedy lawn for quite some time.
Should I reseed or resod brown patch damage?
Reseeding or resodding may be warranted if brown patch has caused severe thinning or dieback of the lawn. But minor damage can often recover through natural regrowth if properly cared for.
Reseeding tips
– Conduct major reseeding in fall when conditions favor seed germination and establishment.
– Lightly rake or vertical mow patchy areas to loosen the soil and remove some thatch.
– Apply starter fertilizer to encourage quick rooting and growth. Use a high-phosphorus formula.
– Select a grass seed mix suitable for your climate and sun exposure. Choose disease-resistant cultivars if available.
– Water newly seeded areas frequently to maintain even moisture. Reduce watering frequency as grass matures.
Sodding advice
– Time resodding for early fall so the new sod has time to root before winter.
– Remove dead grass and soil from patch. Tamp the soil firmly prior to laying new sod.
– Stagger and tighten sod seams. Roll lightly after installation to improve contact with soil.
– Mist sodded areas twice daily for two weeks to prevent drying out. Avoid heavy watering that can dislodge the sod.
With proper follow-up care, newly seeded or sodded lawns can re-establish and fill in bare spots caused by diseases like brown patch. Overseeding thin areas in fall also helps improve lawn density.
Key takeaways
– Brown patch causes roughly circular dead patches scattered throughout cool-season lawns.
– The disease is most prevalent when temperatures are 60-90°F coupled with extended leaf wetness.
– Improve drainage, reduce thatch, and avoid overfertilization to minimize brown patch issues.
– Fungicides containing azoxystrobin, propiconazole or myclobutanil can be applied curatively at first onset.
– Affected lawns often recover within 7-14 days if conditions dry out. Reseed or resod extensive damage in fall.
– The causal fungus persists in the soil to incite new infections when favorable weather returns.
