Ascochyta leaf spot symptoms may develop throughout the growing season but are more common during hot, droughty periods that were preceded by cool, rainy conditions. Large irregular patches of turf rapidly turn a straw-color and appear dead. The overall appearance of the disease may resemble drought stress, except that the symptoms of Ascochyta blight
appear quickly, sometimes overnight. Blighting is usually restricted to the leaves; bluegrass crowns and roots typically are not killed. Conditions that favor Ascochyta blight are poorly understood. The disease occurs in late spring and summer and appears to be enhanced by soil moisture fluctuations, especially drought stress caused by watering restrictions and poor irrigation system coverage. However, the disease may also develop during periods of hot weather preceded by unusually wet
soil conditions caused by excessive rain or over-irrigation. Mowing, foot traffic, etc may enhance the visual presence of the disease. Remember that Ascochyta blight is primarily a foliage and not a root or crown disease. Therefore individual bluegrass plants are usually not killed. Given enough time, usually several weeks, depending on weather, new leaves will emerge from the surviving shoots. Be patient following a disease outbreak and maintain normal management practices.
Visual Characteristics:
Dollar spot is caused by a fungal pathogen that blights leaf tissues without killing turfgrass roots or crowns. This lawn fungus is named for the light tan, roughly circular patches it creates on your lawn. In the early stages, each spot can be about the size of a silver dollar. As this lawn disease progresses, the patches can bleed into each other to form large, irregular discolored spots, several feet in diameter. Each affected leaf blade will show a distinct pattern of straw-colored, tan bands across the blade, often with reddish-brown margins above and below each band. Dollar Spot attacks leaf blades, not roots or soils.
Visual Characteristics:
Rust diseases are characterized by yellow to dark brown urediospore infestations that, from a distance, make turf stands appear orange or yellow. These rust-colored urediospores protrude through the plants epidermis causing spots that elongate parallel to the leaf or stem axis. When rust is severe, areas of infected turf appear thin, weak and are have a red, brown, or yellow tint. Rust populations sporulate at a variety of temperatures, but generally optimal temperatures for epidemics are between 68° and 86° F. Proper irrigation can often eliminate rust as a major problem. If the turf is mowed once per week, the disease severity tends to diminish as well. The removal of clippings that are infected with spores can serve as a means of reducing the spread of inoculum.
Visual Characteristics:
Symptoms first appear as small dark purple to black colored spots on the leaf blade. As the spots enlarge, the centers often turn light tan. In warmer temperatures, greater than 85° F, the entire blade often appears dry and straw colored. The disease is mostly confined to the leaf blades during the cool weather, but can infect leaf sheaths, crowns and roots during hot, humid weather. Leaf spot is a warm-weather disease, but the pathogen overwinters as dormant mycelium in infected plants and dead grass debris. The disease is most severe when temperatures are above 90° F and humidity is high. Conditions of drought stress followed by rewetting intensify the disease. Light, daily, midday irrigation applications, avoiding drought stress when the pathogen is active, will help to reduce or even prevent development of the disease. Avoid irrigation during the late afternoon and early evening during summer months.
Visual Characteristics:
Pythium first appears as circular reddish brown spots in the turf, ranging in diameter from 1 to 6 in. In the morning dew, infected leaf blades appear water soaked and dark and may feel slimy. When spots are wet with dew, purplish gray or white cottony fungal mycelia can be seen on the outer margins of the spots. Infected grass plants collapse quickly, and when conditions are conducive, spots may coalesce and large areas of turf can be lost in a short period of time, even overnight. As a warm-weather disease of cool season grasses, the disease is most destructive when temperatures are between 85° and 95° F. When evening temperatures average 68° F or higher, outbreaks will typically first appear in low areas, or poorly drained areas where soil moisture is maintained. Humid periods further favor disease development.
Visual Characteristics:
Brown patch appears as circular patches, ranging from a few inches to several feet in diameter. The infected leaves first appear water soaked and dark, eventually drying, withering, and turning dark brown. A dark "smoke ring" often surrounds the outer margins of the diseased area when humidity is high and disease is actively growing. Leaves in the blighted area are usually killed, and the disease can rapidly kill large areas of turfgrass in short periods of time under conducive conditions. Brown patch survives as a saprophyte in the thatch, but when soil temperatures rise above 60° F , the fungus will begin to grow. While growing in a circular pattern, the fungus will begin to infect turfgrass foliage when air temperatures are above 80° F and when nighttime temperatures are in the 70's with high humidity.
Visual Characteristics:
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