Common Lawn Diseases
Disease Identifier
Our practical guide for grass disease identification
There are many diseases that occur in lawns. Most of the diseases are caused by various fungal strains, either on the plant itself or in the soil. Turf diseases are found in most conditions, meaning both warm and cool season grasses are susceptible.
Grass diseases can be caused by environmental conditions or factors, such as:
cold and extended wet periods
warm and humid conditions
drought and stress
high soluble salts and poor nutrition
soil compaction
chemical damage, which can be a result of your maintenance practises and misuse of other products.
Careful identification of the cause of a problem and the disease is important for the selection of the correct control product and procedures. In some cases, the problem with your lawn might look like a disease, but could be the result of pests or weeds. So it’s important to contact the Lawn doctor team for advice if you’re unsure what’s affecting your lawn
Brown Patch
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Rhizoctonia solani
DISEASE OF FOLIAGE AND/OR ROOTS
Susceptible Turf
Winter Grass, Couch, Bent Grass, Fescues, Kentucky Blue Grass, Ryegrass and Buffalo Grass
Symptoms
Brown discoloured circular patches, from a few centimetres up to a metre in diameter, sometimes with a smoke ring of mycelium around the edges.
“Smoke rings” appear as thin brown borders around the diseased patches in the early morning.
Infected leaves are water-soaked and dark, later dying and turning dark brown.
After the infected leaves die, new leaves can emerge from the surviving crowns.
On wide bladed species, leaf lesions develop with tan centres and dark brown to black margins.
Conditions Favouring Disease
High relative humidity and temperatures of over 28°C during the day and over 15°C at night.
More than 10 hours a day of foliar wetness for several consecutive days.
Turf grass species are most affected when night temperatures are consistently above 20°C with high humidity or moisture.
Management Tips
Use low to moderate amounts of nitrogen, moderate amounts of phosphorous and moderate to high amount of potassium.
Avoid nitrogen applications when the disease is active.
Increase the height of cut.
Increase the air circulation.
Minimise the amount of shade.
Irrigate turf early in the day.
Improve the drainage of the turf.
Reduce thatch.
Remove dew from turf early in the day.
General Comments
The symptoms of Brown Patch can vary depending on the grass cultivar, climatic and atmospheric conditions, soil and intensity of the turf grass management. Brown Patch infestation is more severe when the turf is cut to a height less than the optimum for the turf species being grown.
Anthracnose
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Colletotrichum spp.
DISEASE OF FOLIAGE AND/OR ROOTS
Susceptible Turf
Winter Grass, Bent Grass, Kentucky Blue Grass, Fescue & Couch
Symptoms
Leaves of infected plants turn yellow to a light tan to brown before dying.
Younger leaves often turn red.
Basel stem and leaf sheath’s rot, affected plants are easy to pull out.
Infected areas are seen as irregular shaped patches.
Affected patches are a reddish brown colour turning yellow then tan to brown.
A black stain may occur at the base of infected plants.
Fruiting bodies have pink spore masses and spiny setae.
Conditions Favouring Disease
Warm, humid conditions favour disease development.
Anthracnose favours temperatures over 25°C.
It is necessary for a film of moisture to be present on either the roots or foliage for infection to occur.
More than 10 hours a day of leaf wetness for consecutive days.
Hot summers in cool temperature areas are when the disease is most noticeable.
Soil compaction and low amounts of nitrogen also contribute to disease occurrence
Management Tips
Decrease the foot traffic.
Maintain adequate nitrogen and balanced fertility.
Irrigate the turf grass just enough to prevent wilting.
Do not core aerate while disease symptoms are present.
Core aerate and overseed in autumn.
Convert to less susceptible varieties on fairways.
Avoid management practices which encourage humidity and extended leaf wetness.
Make preventative fungicide applications where the disease is a chronic problem.
General Comments
Anthracnose typically infects turf grass, particularly Winter Grass during warm weather when the turf grass canopy is wet and or humid.
Pythium Blight
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Pythium spp.
DISEASE OF FOLIAGE AND/OR ROOTS
Susceptible Turf
Mature cool and warm season turf species
Symptoms
Pythium Leaf Blight appears suddenly during hot, humid weather.
Patches occur these patches can enlarge at a rapid rate.
In the early morning, grass leaves appear water-soaked and dark in patches.
When rubbed between the fingers, these water-soaked patches feel oily.
Infected leaves become light tan to brown, shriveled and matted when dry.
When humidity remains high, especially at night, the collapsed leaves become matted and covered with a fluffy white mass of fungal mycelium.
Conditions Favouring Disease
Hot days (30°C – 35°C), humid or rainy weather when night temperatures are warm (above 20°C).
Relative humidity exceeding 90% for at least 14 hours and a minimum temperature not falling below 20°C.
Lush, dense grass growing under high nitrogen fertility is especially susceptible to attack.
Turf areas with poor drainage and air circulation.
Management Tips
When establishing a new area, provide for good surface and subsurface drainage.
Avoid over-watering new plantings and avoid watering late in the day.
On established turf water early in the day.
Water infrequently and deeply.
Removal of excessive thatch.
Do not over fertilise turf with nitrogen.
Promote good light penetration into the turf canopy.
Increase air circulation to speed the drying process of the turf.
General Comments
Excessive moisture is required before Pythium spp. can cause extensive damage. Pythium Leaf Blight may be more severe in alkaline soils.
Spring Dead Spot
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Leptosphaeria korrae
DISEASE OF ROOTS
Susceptible Turf
Common Couch, South African couch grass and their hybrids
Symptoms
Circular patches of bleached, straw coloured dead grass appear in spring as the dormant grass regrows.
Patches are also visible in autumn and winter after a series of unusually cool days or wet, cold weather.
Patches are a few cm to 1 m in diameter.
Patches reappear and expand in the same spot for 3 or more years.
After 2 to 3 years, the centres of active patches may remain alive, and the patch takes on a “ring-like” appearance.
Roots of affected plants turn dark brown to black and are severely rotted.
Regrowth of grass into affected patches is slow and patches may remain barren or fill with weeds.
Conditions Favouring Disease
Most active when temperatures are cool (12°C to 14°C) and soil is moist.
Roots of Couch grow most rapidly at 24°C to 29°C and extremely slowly at 15°C, thus the fungus has a competitive advantage at low temperatures.
Spring Dead Spot favours cool, wet weather in the spring and autumn and daily temperatures of less than 15°C.
This disease is typically found where thatch is more than 1.2 cm thick and in locations with poor drainage and low potassium levels.
Heavy applications of nitrogen in late summer often increase disease severity the following spring.
Spring Dead Spot is more severe on turf that is over three-years old and in locations with long dormancy and cold temperatures.
Management Tips
Preventative systemic fungicide applications during late summer and autumn.
Good fertiliser management especially nitrogen and potassium.
Control weeds in affected turf to enhance recovery from Spring Dead Spot.
Apply moderate to high levels of phosphorous, potash and minor elements.
Improve drainage of turf and reduce thatch.
General Comments
Spring Dead Spot is typically a disease of mature turf that is intensively managed.
Dollar Spot
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Sclerotinia homoeocarpa
DISEASE OF FOLIAGE
Susceptible Turf
All turf species
Symptoms
Closely mowed areas – sunken circular tan coloured spots (less than 5 cm).
May coalesce into larger areas – especially higher mowed turf.
Closer inspection reveals water soaked lesions that will turn tan (hourglass) with definite reddish-brown margins.
Infection will rarely progress to crown or kill plants completely despite leaves being totally blighted.
May be confused with early Pythium Blight and Red Thread.
Humid, cool conditions may see the development of white mycelial growth on infected tissue.
Conditions Favouring Disease
Temperature ranges of 15°C to 30°C and continuous high humidity.
Warm humid weather with cool nights that produce heavy dews.
When the micro-climate temperature reaches 16°C the fungus resumes growth.
Low nitrogen levels.
More severe in dry soils.
Management Tips
Preventative fungicide program.
Provide adequate level of nitrogen, particularly in the spring and early summer.
Mow grass at regular intervals.
Reduce thatch.
Increase air circulation.
Irrigate turf deeply and as infrequently as possible to avoid drought stress.
Remove dew from the turf early in the day.
General Comments
This fungus overwinters as sclerotia and as a dormant mycelium in the crowns and roots of infected plants. Soil pH has little or no effect on Dollar Spot severity.
Fairy Ring
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Basidiomycetes in the order Agraricales are capable of causing fairy rings
DISEASE
Fairy Ring is a unique disease as its symptoms are not directly caused by fungal pathogens. Instead, the Fairy Ring pathogens cause symptoms indirectly, by changing the chemical and physical properties of the soil.
Fairy Ring can present in rings or arc shapes or irregular patterns. Type II and III symptoms are not devastating to turf, however they do detract from uniformity and can affect playability, and in most cases management is required.
As the causes and symptoms can vary, curative fungicide applications can be unreliable. For the best control of Fairy Ring, a preventative strategy should be used.
Susceptible Turf
Occurs in all turfgrasses.
TYPE I Fairy Ring
Symptoms: Damaged or dead turf from drought stress. They may have fruiting bodies present.
Causes:
Hydrophobic (water-repellent) thatch and soil.
Accumulation of ammonium to toxic levels.
Release of hydrogen cyanide or other toxins into the root zone.
Type II Fairy Ring
Symptoms: Rings of dark green or quickly growing turf. These symptoms usually occur early in the season, and indicate that more severe Type I symptoms may follow. They are most evident in under-fertilized turf. They may have fruiting bodies present.
Cause:
Release of nitrogen and other nutrients into the soil.
Type III Fairy Ring
Symptoms: Mushrooms or other fruiting bodies produced in a ring with no visible effect on turf growth. They are most common during periods of wet weather preceded by drought.
Causes:
Mycelial mass buildup around the outer ring
Conditions Favouring Disease
Fairy Rings are more severe on light soils, which have low fertility and low moisture content.
Turf with a significant thatch layer.
Drier areas have significantly more Fairy Rings than higher rainfall areas.
Management Tips
Avoid using root zone mixes with high levels of undecomposed organic materials.
Reduce thatch by vertical cutting.
Core aerify.
Irrigate deeply.
Use nitrogen and iron fertilisers to mask symptoms on some types of Fairy Ring.
Use soil wetting agents to help penetrate hydrophobic areas.
General Comments
Fairy Rings are more prevalent and damaging on lightly water and fertilised fairways and lawns than on well irrigated and fertilised turf. Fairy Rings typically occur in spring and summer, however they can also occur on cool-season turfgrass in mild winter climates. The most common Basidiomycetes in Australia are species of Lycoperdon; Marasmius; Tricholoma; however there are over 50 causal organisms.
Rusts
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Puccinnia & Uromyces species
DISEASE OF FOLIAGE
Susceptible Turf
All cool season turfgrass species.
Symptoms
Early symptoms of Rust diseases appear as light-yellow flecks on leaves or stems.
The flecks enlarge, elongate, and turn yellow in colour.
The yellowed area of the infected spots enlarge and elongate parallel to the leaf or stem axis as the infection matures.
The leaf blade turns yellow starting at the tip and progressing to the base.
The infected areas rise above the epidermis and then rupture, releasing spores that are yellowish-orange to reddish-brown in colour.
Severe disease infection causes the shoot to turn yellowish to reddish-brown and slows growth.
As individual plants die, the turf thins.
Conditions Favouring Disease
Rust diseases typically occur in early spring through mid-summer.
Rusts favour moist, low-light areas.
Leaf wetness is required for fungal growth.
Depending on the species, Rusts favour temperatures between 18°C and 30°C.
Severe rust infections occur on slow-growing turfgrass particularly those with low nitrogen levels and/or water stress.
Management Tips
Convert to a turfgrass seed blend that is resistant to rust diseases found in the area.
Apply adequate levels of nitrogen and other nutrients
Remove clippings from turf.
Reduce shade and improve air circulation.
Regulate irrigation to minimise the amount of time moisture remains on the leaf surface.
Water deeply and infrequently.
General Comments
Grasses growing under stressful environmental conditions are most easily parasitised by the Rust fungi.
Helminthosporium disease
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Bipolaris spp., Drechslera spp. and Exserohilum spp.
DISEASE OF FOLIAGE AND/OR ROOTS
Susceptible Turf
All turf species
Symptoms
Helminthosporium symptoms can vary.
Initial symptoms are small lesions on leaf blades.
Leaf tissues turn yellow around these lesions.
Severely infected leaves may die and appear light tan to straw-coloured.
In Couch, Helminthosporium causes dark brown or white “net” blotches on the leaves.
Young seedlings may be killed by the disease, but mature plants will usually overcome the damage during favourable growing periods.
Conditions Favouring Disease
Helminthosponum is able to develop at temperatures between 3°C and 30°C.
Leaf moisture is necessary for infection to occur.
More than 10 hours a day of leaf wetness for several consecutive days.
Poor air movement (high humidity in the micro-climate).
Excessive nitrogen fertiliser.
Any stress situation such as drought, herbicide injury or heavy traffic can increase the severity of the disease.
Management Tips
Maintain healthy turf through proper fertilisation. Pay particular attention to potassium and nitrogen levels.
Irrigate infrequently and deeply.
Avoid late afternoon or evening irrigations.
Do not allow the turf to become extremely dry during warm weather.
Increase air movement and improve turf drainage.
Avoid herbicide applications during critical periods of disease activity.
Disperse traffic in high traffic areas.
Mow turf at recommended height for turf species.
General Comments
Helminthosporium is a complex of diseases previously known as Helminthosporium leaf, crown and root disease.