Schumann, G.L. 2001. Turfgrass Disease Specimens for Teaching. The Plant Health Instructor. DOI: 10.1094/PHI-T-2001-1025-01 Updated 2009
It is challenging to have good summer disease specimens during classes that meet in late fall and over the winter months. Some turfgrass diseases can be readily produced by inoculating pot-grown grass with sterile grains infested with a fungal pathogen and maintaining the turf at 100% relative humidity 4 to 7 days at optimal temperatures for the disease desired. This can be easily done with Pythium aphanidermatum (for Pythium blight), Rhizoctonia solani (for brown patch), and Sclerotinia homoeocarpa (for dollar spot). Students can make microscopic observations of hyphal characteristics and, in the case of P. aphanidermatum, sporangia and oospores in infected leaf tissue.
Other diseases are not so easily produced under such artificial conditions. Cup-cutter plugs of symptomatic turf submitted to diagnostic labs often can be maintained for 3 to 7 months in plastic boxes on moist paper towels in refrigerators. It is important to keep the plugs from drying out, but avoid too much moisture which favors excessive mycelial growth. Three diseases that can be maintained with surprisingly good symptoms in this manner are anthracnose (foliar and/or basal rot) (Colletotrichum graminicola), bentgrass dead spot (Ophiosphaerella agrostis), and Fusarium patch or pink snow mold (Microdochium nivale). Similarly, diagnostic lab turf samples with necrotic ring spot (Ophiosphaerella korrae), summer patch (Magnaporthe poae), or take-all patch (Gaeumannomyces graminis) can be maintained in pots in a greenhouse for many months to provide students with good examples of roots infected by ectotrophic hyphae.
Ascochyta, Leptosphaerulina, and Septoria are three common tip blight turfgrass pathogens that all produce fruiting bodies that look quite similar. These fungi often can be found in turfgrasses that have not been closely mown, such as along fences. If the long leaf blades containing the fruiting bodies are cut and allowed to dry, they can be stored in bags or boxes for years. Leaves should be placed on moist paper towels for 15-30 min to rehydrate the leaf tissue. Students can easily observe the fruiting bodies with a dissecting microscope. The fungal genus can be identified by gently pressing on a cover slip to expel the spores while observing the fruiting bodies with a compound microscope. Even if instructors do not have leaves infected with all three fungi, it is a useful exercise to have students determine which fungus is present.
In general, students seem to benefit from observing diseased turfgrass at three levels: by eye, with a dissecting microscope (20-40x magnification), and with a compound microscope. This gives them a better perspective about what kinds of identification they will be able to make in the field and when they will need access to microscopes for accurate diagnosis. Good images of turf symptoms and pathogen characteristics can be found in the cited references.
1) Schumann, G.L. and J.D. MacDonald. 1997. Turfgrass Diseases: Diagnosis and Management CD-ROM. APS Press, St. Paul, MN. (out of print)
2) Smiley, R.W., P.H. Dernoeden, and B.B. Clarke. 2005. Compendium of Turfgrass Diseases, 3d Ed. APS Press, St. Paul, MN.