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Turf necrotic ring spot
Necrotic ring spot is a common disease of turf caused by soil borne fungi (''Ophiosphaerella korrae'') that mainly infects roots (4). It is an important disease as it destroys the appearance of turfgrasses on park, playing fields and golf courses. Necrotic Ring Spot is caused by a fungal pathogen that is an ascomycete that produces ascospores in an ascocarp (6). They survive over winter, or any unfavorable condition as sclerotia. Most infection occurs in spring and fall when the temperature is about 13 to 28°C (5). The primary hosts of this disease are cool-season grasses such as Kentucky bluegrass and annual bluegrass (6). Once turf is infected with ''O. korrae'', it kills turf roots and crowns. Symptoms of the disease are quite noticeable since they appear as large yellow ring-shaped patches of dead turf. Management of the disease is often uneasy and requires application of multiple controls. The disease can be controlled by many different kind of controls including chemicals and cultural.
==Hosts and symptoms==
Turf necrotic ring spot is known to infect various bluegrass and turfgrass species, especially the cool-season grasses. The fungus also infects fescues and bentgrasses (11). It is common in sodded lawns, rapidly growing lawns, and lawns with layered soil (3). The pathogen produces circular patches of bald spots that are tan or yellow in color (12). These patches are about 5 to 10 cm in diameter, but can grow to be about 1 meter in diameter. Eventually, as the infected turf dies, the spots turn brown. Within the patch, there may be areas of living grass at the center, creating a frog-eye appearance that this pathogen is known for. This is the result of the turf in the center surviving or being recolonized by healthy grass (3).
While the infection happens during cooler seasons, such as fall and spring, the symptoms can carry into summer (7). Should the disease continue through the summer, it may cause the crown and roots to become blackened with visible mycelium (11). As previously mentioned, this disease alters the grass by creating patches of yellow or tan dead grass (1). Another possible symptom is leaf lesions. Leaf lesions are often common among fungal diseases. If there are leaf lesions on the blade, the lesions will be inconsistent in terms of size and shape. The lesions may also be varying colors, such as yellow, tan, or dark brown (11).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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