Turf affected: Fescue, Ryegrass and Bluegrass
Symptoms: Circular brown patches up to 3 feet in diameter that develop during hot, wet weather. Infected leaves become dark, wilt and die quickly when the disease is active. The entire patch will eventually become a brownish tan color.
Disease occurrence: Mid-June to early September
Turf affected: Bluegrass and Ryegrass
Symptoms: Straw-colored patches 2 to 6 inches in diameter. Hourglass shaped lesions with reddish-brown margins develop across the leaves.
Disease occurrence: Late March to early November.
Turf affected: Kentucky bluegrass (especially common bluegrasses), fescues and other lawn grasses
Symptoms: Small lesions on leaf blades. Dark colored spots that eventually turn light tan but remain bordered by a dark brown outer edge. Eventually these plants die out and turn brown or straw colored, this can occur in patches.
Disease occurrence: Spring, typically during time of cool, wet weather
Turf affected: All species
Symptoms: Pinkish red threads that form around the leaf blades and bind them together. Eventually, the affected turf will turn brown. The red threads will be most visible when the turf is wet and you may see red spores on your mower and shoes.
Disease occurrence: Early spring
Turf affected: Bluegrass, Ryegrass, and Tall Fescue
Symptoms: Small yellow specks on leaves and stems develop into orange or red pustules. Heavily infected lawns may have an orange or reddish hue, and the lawn may begin to thin out. This “rust” will be visible on shoes and mowers after being on the lawn.
Disease occurrence: Summer to early Fall
Turf affected: Most cool season turf grasses in the northern US
Symptoms: Symptoms first appear in the lawn as circular, straw colored patches when the snow melts in the spring. These patches continue to enlarge as long as the grass remains cold and wet. Grass within the patch often has a matted appearance and colored fungal growth. The fungal growth may cover the entire patch or develop along the margins, with gray snow mold being white to gray in color and pink snow mold being white to pink in color.
Disease occurrence: Early Spring as the snow melts
Affected: Trees and Shrubs
Symptoms: Plants infected with powdery mildew look as if they have been dusted with flour. It usually starts off as circular, powdery white spots, which can appear on leaves, stems, and sometimes fruit and usually covers the upper part of the leaves. The older leaves are affected first and turn yellow and dry out and may cause some leaves to twist, break, or become distorted.
Disease occurrence: Powdery Mildew usually appears late in the growing season.
Turf affected: Mixed annual, fine fescues, Kentucky bluegrass/bentgrass
Symptoms: Summer patch may begin as a small circular patch that can progress to a large patch if conditions favor the disease development. Patches initially take on a yellow color, which then turns to tan or straw-brown color as the plant dies.
Disease occurrence: Midsummer during extended periods of high temperatures (> 82°F) following wet weather or heavy irrigation. Wet periods followed by dry conditions can also bring on severe symptoms. The disease does not appear during the cool weather of spring and fall. Summer patch is more frequently observed in areas that receive heavy traffic, poor air circulation, and inadequate drainage.
Turf affected: Bentgrasses and Ryegrasses
Symptoms: Pythium blight first appears as small, irregularly shaped spots ranging from ½ inch to 4 inches in diameter. Leaves appear water-soaked in appearance at first, then shriveled and diseased patches fade to a light brown or gray color. With high humidity in the early morning or throughout the day, diseased leaves may be covered with the white, cobwebby, moldlike growth of the causal fungus.
Disease occurrence: Turf blighting and disease development will be most rapid and severe at air temperatures from 85° to 95°F. As the air temperature approaches 95°F, destruction of grass stands can occur in a very short time.