The symptoms of brown patch vary according to mowing height. In landscape situations, where mowing height is greater than 1", brown patch appears as roughly circular patches that are brown, tan, or yellow in color and range from 6" to several feet in diameter. The affected leaves typically remain upright, and lesions are evident on the leaves that are tan in color and irregular in shape with a dark brown border. When the leaves are wet or humidity is high, small amounts of gray cottony growth, called mycelium, may be seen growing amongst affected leaves. In close-cut turfgrasses (1" or less), brown patch develops in roughly circular patches, ranging from a few inches to several feet in diameter, that are brown or orange in color. Distinct foliar lesions are not visible and mycelium is typically not present, but a black or dark gray ring, called a smoke ring, may surround the brown patches. The smoke ring is evidence of active disease development and is only present when the turfgrass leaves are wet or humidity is near 100%.
Under favorable environmental conditions brown patch symptoms may develop overnight. On creeping bentgrass and annual bluegrass greens and tees, brown patch development results in circular olive green stains, ranging from 4 to 12 inches in diameter. Leaf blades within the patch turn brown after infection, while a gray-white band is normally evident at the perimeter of active patches.The band (often called a smoke ring) is caused by advancing mycelium and watersoaked infected leaves. Smoke rings may occur on taller mown turf, but are much less evident. Figure 4 shows advancing mycelium surrounding brown patch on perennial ryegrass. Individual lesions on leaf blades with brown margins occur on all affected grass species but are most evident on tall fescue. Brown patch is a summer disease. The pathogen becomes active during hot, humid periods when dew periods exceed 10 hours and nighttime temperatures remain above 65F. Also, outbreaks will be more severe when nitrogen fertility is excessive during disease-favorable weather.
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