We received an ornamental grass sample from the Decatur area this week that has me a little stumped, and I'd like your help in solving this mystery. Based on the sample and accompanying description, Tom Voigt tentatively identified the grass as Miscanthus 'Purpurascens'. The client says the grass planting was installed 6 years ago and the symptoms probably began in early August this year. From the dried-down sample, I observed minute, irregular, reddish lesions on the leaves. Several days in a humidity chamber revealed only fruiting bodies and spores of several common saprophytic fungi. Moreover, no fruiting bodies or spores were associated with lesions and the surrounding tissue.
A review of the literature and Internet content for diseases and abnormalities of Miscanthus revealed little. The University of Maryland's Diagnostic Web Site indicates that anthracnose is a common disease of Miscanthus, but the symptoms (dark, irregular lesions) and signs reported are not consistent with our sample. In 1991, researchers from Japan reported (Journal of General Virology, vol. 72) identifying Miscanthus streak virus on Miscanthus sacchariflorus. Again, the symptoms (chlorotic streaking) are not what I saw. Finally, in 1996, USDA researchers in Maryland reported (Plant Disease, vol 80:9) specific fruiting bodies and reddish brown spots to oval streaks on leaves and sheaths on several varieties of Miscanthus sinensis. They identified the causal fungus as Leptosphaeria (anamorph = Stagonospora) and called the disease Miscanthus blight. Although the symptoms on our sample are similar, preliminary culture did not reveal the fungus. To prove or disprove my initial findings, I intend to use the specific isolation/culture protocol used by the USDA researchers.
It is possible that this is not an infectious disease. With the localized temperature and moisture swings this growing season, I wonder if the some ornamental grass varieties might be reacting by flecking/spotting or simply shutting down prematurely. If you have observed similar or other abnormal symptoms on well-established ornamental grasses this year, please contact me, (217)244-9646 or firstname.lastname@example.org.
For more information about ornamental grasses, see these University of Illinois Extension Web sites: www.urbanext.uiuc.edu/grasses and www.outreach. uiuc.edu/grassid.