Season: Mid to Late Summer

Favorable Conditions: High temperatures (75 to 95 degrees F), heavy or dense thatch, high humidity, lush or weak growth fr0m over fertilizing, and excessive moisture create perfect conditions for this disease to thrive in.

Appearance: Large, irregular circular areas, up to several feet in diameter, occur throughout the lawn. The patches usually have a brownish to gray discoloration with a water-soaked appearance around the edges.Normally, only the leaves and stems are attacked.

Susceptable Grasses: Serious disease in the South on centipedegrass and St. Augustinegrass. It also attacks bentgrass, bermudagrass, rye grass, fescue, and zoyiagrass

Resistant Varieties: "Manhattan II", and "Pennant" perennial ryegrasses; "Rebel II" and "Wrangler" tall fescues.

Season: Spring to Fall

Favorable Conditions: Moderate temperatures, excess moisture, and heavy thatch all contribute to this disease; it is common near foggy coasts. Nitrogen-deficient lawns develop more dollar spot than those that are fertilized adequately.

Appearance: Grass dies off in small spots from 1 to 5 inches in diameter, but the spots may coalesce into large areas. Spots are usually bleached from tan to straw-colored. White, cobwebby fungus threads may be seen in early morning.

Susceptible Grasses: Most severe in bentgrass and bermudagrass, but also attacks Kentucky bluegrass, fescue, and ryegrass.

Resistant Varieties: "Biljart", and "Scaldis" fine fescues; "Manhattan II" perennial ryegrass; "Adelphi", "Eclipse", and "Midnight" Kentucky bluegrass.

Season: Spring to Fall

Favorable Conditions: Cool (50 to 70 degrees F), moist conditions are most favorable for the growth of leaf spot. The spots first appear on grass in shady areas of the lawn. They occur most commonly during wet, humid weather or in lawns that are often lightly sprinkled or mowed too closely.

Appearance: The most obvious symptom of this disease is elongated circular spots on grass blades. These spots have a brown or straw-colored center with black to purplish borders.

Susceptible Grasses: Kentucky bluegrass, fescue, and bermudagrass.

Resistant Varieties: "Julia" and "Midnight" Kentucky bluegrasses, "Banner II" fine fescue, "Cimarron" and "Rebel II" tall fescues.

Season: Spring and Fall

Appearance: Small spots that appear water-soaked enlarge rapidly to cover a large part of the leaf. As the spots dry, the leaves fade to a light brown or tan. Pink webs bind the grass blades together. Later, the fungus forms this, red-to-pink, finger-like structures at the tips of grass leaves, which gives the lawn a reddish cast.

Favorable Conditions: Most damaging in spring and fall in temperatures of 68 to 75 degrees F and high humidity. Low levels of nitrogen favor its development. When grass growth slows down due to lack of nitrogen the disease the becomes more prevalent.
Susceptible Grasses: Red Fescue, ryegrass, Kentucky bluegrass, and bentgrass.

Resistant Varieties: "Biljart" and "Claudia" fine fescues; "Chateau" Kentucky bluegrass; "Pennant" perennial ryegrass.

Season: Midsummer to Fall

Favorable Conditions: Moderately warm, moist weather. Dew that lasts for 10 to 12 hours promotes germinations. Stress that restricts growth favors rust.

Appearance: The lawn takes on a rust colored cast, especially noticeable from a distance. Dust-like spores, the main symptom of this disease, form a circular or elongated groups on grass blades. Anything moving through a severely infested area will be covered by the spores and may spread the disease.

Susceptible Grasses: Can affect most types of turfgrass, but Kentucky bluegrass is damaged most frequently.

Resistant Varieties: "America" and "Eclipse" Kentucky bluegrass, and "Manhattan II" perennial ryegrass.

Season: Midsummer

Favorable Conditions: Hot, dry, and windy weather creates an excellent climate for summer patch. It's most prevalent when hot (89 to 95 degrees F), summer days follow warm periods that have alternated between wet and dry weather.

Appearance: Begins as scattered light green patches up to 8 inches in diameter that turn dull tan to reddish brown. In larger diseased patches, the easiest symptom to recognize is the "frog-eye" pattern- an apparently healthy green patch of grass that is partially or completely surrounded by a ring of dead grass.

Susceptible Grasses: Bentgrass, turf-type tall fescue, perennial ryegrass, and some Kentucky bluegrass cultivars.

Resistant Varieties: "America" and "Blue Star" Kentucky bluegrass.