Leaf Smut

• Leaf smut fungi occurs in the spring and fall, when sustained temperatures are between 50 and 60 degrees Fahrenheit. It usually affects bluegrass, fine fescue and perennial rye. This fungus initially manifests by bleaching the color from a patch of grass and stunting its growth. At some point, you'll see black or gray spots form on individual blades of grass. These spots will eventually expand to become stripes, lending this fungi its "stripe smut" alias. Drag a white cloth across the affected grass and you will find the cloth covered in black mold spores.
  
  

Leaf Spot

• Leaf spot fungi can affect trees, shrubs, annuals, bulbous plants, vegetables, fruits and entire lawns. Leaf spot fungi aren't mold; they are actually colonies of millions of mushrooms that are just large enough to see with the naked eye. Colors vary and the individual mushrooms can range from brown to slate gray, but the overall appearance of a fungal colony is a reddish-brown to purple-black. These fungal colonies generally don't negatively affect the overall health of the plant unless they obscure enough of the leaf surface to block sunlight and inhibit photosynthesis.
  
  

Rust

• Rust is a very destructive fungi that initially manifests as yellow or brown pustules on the underside of plant leaves or grass blades. Shortly afterward, red spots will appear on the tops of leaves. As the pustules mature and burst, they turn from red-brown to black, eventually covering the leaves and causing them to drop off and die. Conditions favoring this disease include 10 to 12 hours per day of moisture coverage and 70 to 75 degree air temperatures.
  
  

Pythium Blight

• Pythium blight generally occurs on newly seeded lawns and can manifest as patches of blackened, flattened grass. You may see a cobweb-like mass of fungus on warm, moist nights and mornings. Patches of pythium generally start as small, irregularly shaped spots and join to form patches 1 foot or more in diameter.
  
  

Treatment and Prevention

• You can treat pythium, leaf smut and leaf spot with commercially available fungicide. For pythium, remove all of the affected grass or leaves after treatment and burn them to prevent re-infection. Apply a systemic fungicide to leaf smut in October or early March; water the chemical into the ground thoroughly to kill any fungi in the soil and roots. Both fungicide and sulfur will help to control rust, but apply them early in the growing season to prevent it next year. In all cases, avoid over-watering and keep the lawn clean and mowed to increase air circulation and prevent fungal growth.