Most Common Diseases Affecting Zoysiagrass 

Zoysiagrass is a good choice for any lawn because it is versatile, adapts well to different climates and soil types, and is less vulnerable to disease than some other grasses. But that doesn’t mean it’s indestructible. 

Like any grass, it has some enemies, and we’re going to introduce you to some of the diseases that most commonly afflict Zoysiagrass.

In this article:

• Brown patch 
• Rust
• Fusarium blight
• Crown rot and leaf spot disorder
• Dollar spot
• Powdery mildew
• Fairy rings
• Pythium blight

Brown patch

Brown patch, also known as rhizoctonia blight, is the most common disease in Zoysiagrass, and generally hits newly established lawns harder than established lawns. As the name suggests, telltale signs of the disease include small circular patches of brown, dead, or dying grass. Unchecked, these patches can get to be six feet in diameter.

Causes 

• Excessive buildup of thatch
• Over- application of nitrogen fertilizer during summer
• High humidity

Symptoms

• Light brown circular patches on the affected area
• The appearance of water-soaked grass on the lawn
• Brown or yellow rings of dying grass

Prevention and treatment

To keep your Zoysiagrass lawn healthy, ensure you:

• Water in the early morning but not in the afternoon, and only about once a week
• Remove excess thatch
• Apply one to two pounds of nitrogen fertilizer per square feet of lawn annually between May and April

Rust

Rust, which is caused by the puccinia fungus, is common in early spring and summer. It is more common in lawns that experience drought stress and inadequate soil nutrients. It’s not hard to detect: Its spores leave an orange film on almost everything that touches the infected grass, including shoes and pet paws.

Causes

• Warm, humid conditions
• Persistent drought
• Improper mowing
• Inadequate nutrients in the soil

Symptoms

• Yellow spots on the Zoysia leaf sheaths
• Leaves become discolored and wilt 
• Reddish orange dust during mowing

Treatment and prevention

• Adjust the soil nutrients and ph levels
• Mow to the required heights
• Apply nitrogen fertilizer
• Apply fungicides

Fusarium blight

Fusarium blight is creates large yellow patches on the lawn. Fusarium blight is caused by microdochium nivale fungus, which is common when temperatures are cool, and the snow covering the lawn starts to melt. It attacks golf courses more often than residential turf.

Causes

• Cool temperatures and high humidity
• Excess nitrogen in the soil
• Poorly drained soils
• Excess thatch

Symptoms

• Yellow spots of 1-3 inches in diameter turn brown, forming rings 12-24 inches wide on the grass blades
• Gel-like pink spores on the dead grass
• The deceased leaves turn tan, and turf clumps stick together.

Prevention and treatment

• Use a vertical mower to remove thatch.
• Aerate to improve air flow.
• Water deeply once a week, and early in the morning.
• Apply fungicide.

Crown rot and leaf spot disorders

Crown rot is caused by a fungus that can survive in the soil indefinitely. Wet conditions and heavy soils promote crown rot, which rots the crown and the roots of the plant. The disease also leaves gray leaf spots on the leaf blades.

Causes

• Excess nitrogen fertilizer
• Sudden, heavy rains

Symptoms

• Purple-black spots on the borders of the lawn
• Dark brown to black grass roots
• Leaf blades turn brown, wither, and die.

Prevention and control

Prevention is key, because once crown rot sets in, it is difficult or impossible to eradicate.

• Apply the right amount of fertilizers from May to August.
• Mow to a height of one half to one inch to promote dense grass growth and keep the disease from getting a foothold.
• Mow when dry.
• Test the soil to ensure you maintain the right soil pH to help control the disease
• Use a mulching mower to distribute the Zoysiagrass clippings.

 Dollar spot

Dollar spot is a common Zoysiagrass disease characterized by a straw-colored spot about the size of a silver dollar on the grass leaves. It is caused by Sclerotinia homeocarpa fungus, which is more dominant during summer and the fall.

Causes

• High humidity with low soil moisture content
• Insufficient nitrogen fertilizer
• Poor mowing practices
• Poor thatch management and excessive weeds

Symptoms

• White spots of wilted grass on turf

Prevention and treatment

• Remove thatch to increase soil aeration.
• Apply fast-release nitrogen fertilizer to maintain soil fertility; this may help reverse damage from the disease.
• Irrigate deeply but not frequently.

Powdery mildew

Powdery mildew is caused by erysiphe graminis fungus, which initially appears as small powdery white patches on the upper surface of the Zoysia leaves.

Causes

• High humidity
• Improper aeration
• Excessive use of nitrogen fertilizer
• Excessive shade/inadequate sunlight

Symptoms

• Small powdery white patches on the leaf’s surface spread fast, covering the whole leaf.
• The leaves below the surface turn yellow and eventually die.

Prevention and treatment

• Dethatch to increase air circulation.
• Trim hanging branches to give the grass more sunlight.
• Avoid overwatering your lawn. One inch of water a week is enough.
• Use weed-controlling products.
• Use fungicides containing sulfur to control the disease.

Fairy rings

Fairy rings result from basidiomycetes, or mushroom fungi, that affect the plant tissues. The disease is characterized by dark green arcs or circles on the lawn. Fairy disease is most likely to develop during spring and fall when the fungi feed on the decaying tissues, forming a waterproof layer that reduces water infiltration into the soil.

Causes

• Excess nitrogen in the soil
• Drought
• Poor mowing practices
• Poor thatch management

Symptoms

• Dark green rings, either circular or semicircular, on the lawn
• Presence of dead or dying grass on your lawn
• The appearance of mushrooms

Prevention and treatment

• Use a vertical mow to remove thatch and reduce soil compaction.
• Apply nitrogen fertilizer
• Aerate
• Water the grass regularly to remove the waterproof layer
• Top with high-quality sand to neutralize the organic matter in the lawn

Pythium blight

Pythium blight appears as sunken oily-looking patches of the grass that can grow to about 12 inches wide. It is also known as cotton blight or grease spot disease. Pythium blight is caused by pythium spp fungus, which is common with Zoysiagrass.

The mycelium produced by the fungus can survive in the soil and on dead or cut grass. Under warm, damp conditions, it only takes two hours to produce spores and infect other plants.

Causes

• High humidity
• Warm, damp conditions
• Poor drainage

Symptoms 

• Wet, greasy patches that develop gray mold on the diseased turf
• Green to reddish-brown color on the blades, which later withers and dies.

Prevention and control

• Avoid mowing when the grass is wet.
• Don’’t overwatering your lawn.
• Apply fungicide as needed.

Frequently asked questions (FAQs)

Takeaways 

Despite being drought-tolerant, Zoysiagrass is susceptible to disease during extended periods of drought. Check your lawn regularly for signs of disease. You can also seek help from a Lawn Love lawn care professional to help you take care of your Zoysiagrass lawn.

Main photo credit: Bill Wilson | Flickr | CC BY 2.0