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Symptoms and Signs

Brown Patch
Brown patch, caused by Rhizoctonia solani, is a disease of cool-season grasses, including bentgrasses, bluegrasses, fescues, and ryegrasses. Brown patch commonly occurs during periods of warm and humid weather. As the name implies, gross symptoms of brown patch are brown or tan patches of diseased turf ranging in diameter from 5 cm (2 in.) up to 1 m (3 ft) or more in diameter (Figure 1, Figure 2, Figure 3, Figure 4, Figure 5). When close-cut turf (<2.5 cm or 1 in.) is wet, brown patches are often surrounded by a dark brown or gray ring called a "smoke ring" (Figure 6, 7). The smoke ring is evidence of active fungal growth on the turf foliage and is an initial sign of brown patch development. Brown patch typically does not result in damage to all tillers within a developing patch (Figure 8), therefore, the turf may recover when disease pressure is reduced by change in weather conditions or implementation of control practices.

Figure 1	Figure 2
Figure 3	Figure 4
Figure 5	Figure 6
Figure 7	Figure 8

Symptoms observed on individual plants vary according to the height of mowing. On turf maintained above 2.5 cm (1 in.), irregular silver-gray or tan lesions with a thin, dark brown border are observed on the leaves (Figure 9). On close-cut turf (<2.5 cm or 1 in.), no distinct lesions are readily observed, but the symptoms appear as general leaf necrosis.

Figure 9

Large Patch
Rhizoctonia solani also causes large patch, a disease of warm-season grasses, including bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass. Large patch occurs during the spring and fall, when warm-season turfgrasses are entering or exiting their period of winter dormancy. Circular patches of diseased turf are observed, ranging in diameter from less than 1 m (3.3 ft) up to 8 m (26.4 ft) (Figure 10, Figure 11, Figure 12, Figure 13). Leaves of recently infected turf, located at the periphery of the patch, may appear orange in color (Figure 14). Some patches may be perennial, recurring in the same location and expanding in diameter year after year. In contrast to brown patch, R. solani infection of warm-season grasses occurs on the leaf sheaths, where water-soaked, reddish-brown or black lesions are observed (Figure 15). Foliar dieback from the leaf tip toward the base occurs as a direct result of these leaf sheath infections.

Figure 10	Figure 11
Figure 12	Figure 13
Figure 14	Figure 15

Leaf and Sheath Spot
Leaf and sheath spot is a collective term used for turfgrass diseases caused by two Rhizoctonia species: R. zeae and R. oryzae. Because these diseases are relatively uncommon in occurrence, their etiologies have not yet been thoroughly characterized. Rhizoctonia zeae has been isolated from lesions on tall fescue that appeared similar to brown patch lesions. On creeping bentgrass, R. zeae has been associated with patches of diseased turf ranging in color from dark gray or brown to orange (Figure 16). A “smoke ring” similar to that associated with brown patch may also appear (Figure 17). On centipedegrass and St. Augustinegrass, both R. zeae and R. oryzae cause leaf sheath lesions, similar to those induced by R. solani. In addition, R. zeae has been associated with a diffuse foliar blight of bermudagrass. Further research on the etiology of these diseases is required to facilitate accurate disease diagnosis and management.

Figure 16

Figure 17

Yellow Patch
Yellow patch, caused by R. cerealis, is a disease of cool-season turfgrasses that occurs during periods of cool, wet conditions. This disease has also been observed infrequently on bermudagrass and zoysiagrass. In turfgrass swards, yellow to tan, irregularly shaped patches or rings are observed, ranging in diameter from 15 cm (6 in.) up to 1 m (3.3 ft) (Figure 18; Figure 19). Rhizoctonia cerealis incites a foliar blight, but no distinct foliar lesions, smoke rings, or any other signs of pathogen activity are readily observed. A disease similar to yellow patch has been observed in Japan, where the pathogen has been identified as Rhizoctonia AG-Q.

Figure 18

Figure 19

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