![]() ![]() Pythium aphanidermatum and many other turfgrass-associated Pythium form lobed sporangia ( Figure 17) while other Pythium species may form spherical sporangia ( Figure 18). produce sack-like structures called sporangia, which vary in shape from filamentous to spherical. For the most part, when submitted disease samples are diagnosed as Pythium blight, the species of Pythium is not normally identified and reported.Īsexual reproduction. aphanidermatum and other Pythium species from samples submitted to plant disease diagnostic clinics is not readily known. Pythium aphanidermatum is the primary species associated with Pythium blight in the US, however, as many as 15 other species of Pythium have been associated with foliar blight symptoms. and other oomycete pathogens behave quite differently from fungi and often require distinct methods of management. Members of the genus Pythium belong to a group of organisms known as “oomycetes.” Although appearing similar to fungi, Pythium spp. homoeocarpa hyphae is generally larger than R. Right-angled branching is also a characteristic that distinguishes R. The branch hyphae appear slightly constricted at their origin, and a septum is present near the branch origin. In addition Rhizoctonia produces hyphae that branch at right and acute angles to the main hypha ( Figure 16B). ( Figure 16A), whereas Rhizoctonia and Sclerotinia spp. The most notable difference is the absence of septa in hyphae of Pythium spp. Even though the aerial mycelium of the three pathogens is similar in appearance, microscopic observation of the hyphae reveals major differences. is similar in appearance to mycelium produced by Sclerotinia homoeocarpa, which causes dollar spot and Rhizoctonia solani, the causal agent of brown patch. However, the latter pathogens produce foliar symptoms that are distinct from those produced by Pythium spp. in the morning after a night of rain or heavy dew. The mycelium is most abundant when infected leaves are wet, e.g. Pythium blight is also called "cottony blight" which refers to the cotton candy-like growth of white, fluffy aerial mycelium growing from infected turfgrass foliage ( Figures 13-15). In addition to foliar blight, crown, stolon and root rot are frequently associated with Pythium blight. Pythium blight can also appear as streaks in areas where the fungal-like pathogen is spread by flowing water or mowing equipment ( Figure 12). Patches of infected grass can enlarge and coalesce, causing severe damage to lawns, golf courses and athletic field turf ( Figures 10-11). No distinct lesions are formed on infected leaves, which often feel slimy or greasy when rubbed between two fingers. ![]() These patches can range in size from 20 cm (0.4 to > 8 in.) in diameter. Initial symptoms appear as dark green to purple water-soaked leaves that aggregate into circular or irregularly shaped patches in turfgrass swards ( Figures 1-9). The disease is particularly severe when daytime temperatures exceed 28☌ (82☏) and night temperatures fail to fall below 20☌ (68☏). Symptoms of Pythium blight are evident during warm, humid weather when turfgrass leaves are wet for at least 12 hours. Initial symptoms of Pythium blight in tall fescue (Courtesy L.L. University of Georgia, Griffin Campus, Griffin, GA HOSTS: Warm- and cool-season turfgrasses. PATHOGEN: Many Pythium species (primarily Pythium aphanidermatum in the US) ![]()
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