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Symptoms and Signs

Symptoms

Anthracnose of turfgrass is a foliar disease or a basal rot of the lower stem. Foliar lesions on creeping bentgrass appear reddish-tan (Figure 1). In some cases discrete leaf spot symptoms may not develop, and instead, older leaf blades are completely water-soaked (Figure 2). The foliar phase of anthracnose is also common on annual bluegrass where symptoms include elongate, chlorotic (yellow) leaf spots with small, black, spore-bearing structures (acervuli) in the center (Figure 3). The leaves turn brown and may be peppered with acervuli (Figure 4).

Figure 1	Figure 2
Figure 3	Figure 4

Basal rot occurs when leaf sheaths at the base of tillers are colonized by the fungus. Infected tissue appears dark brown to black, and leaf blades appear orange to yellow and are devoid of lesions (Figure 5). Creeping bentgrass stolons may also become infected (Figure 6).

Figure 5

Figure 6

An anthracnose outbreak in a golf putting green, tee, or fairway can have a patchy (Figures 7, 8) or diffuse (Figure 9) appearance. Foci of diseased plants can range from small irregular patches that measure 1 to 10 cm (>0.5 to 4 in.) to large areas that measure >1 m (> 3 ft). Severe outbreaks often result when the pathogen selectively kills invading annual bluegrass in creeping bentgrass putting greens (Figures 9, 10). Anthracnose can also develop on creeping bentgrass putting greens that have little or no annual bluegrass infestation (Figure 11). Damage to creeping bentgrass can progress to cause significant plant thinning within individual patches. The reason for patch formation is uncertain, but some patches may represent susceptible biotypes of bentgrass that segregate from more resistant biotypes within a putting green (Figure 12).

Figure 7	Figure 8	Figure 9
Figure 10	Figure 11	Figure 12

Signs

The most prominent sign of anthracnose is the presence of tufts of black setae (sterile, hair-like fungal structures) on plant tissue. Setae can be observed with a 10X magnification lens and are often abundant on dead or dying leaves, leaf sheaths, or stolons (Figure 13). Setae denote the presence of acervuli (Figure 14), fruiting bodies which produce asexual spores (conidia) contained in a mucilaginous matrix (Figure 15). The mucilaginous material prevents desiccation damage and premature germination of conidia. Conidia are hyaline (clear), crescent-shaped, and single celled (Figure 16). Conidia may be confused with those of Fusarium spp. and Microdochium nivale (cause of pink snow mold), but these species usually form conidia that have two or more cells.

Figure 13	Figure 14
Figure 15	Figure 16

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