Managing Anthracnose on Golf Course Putting Greens (P1)
Anthracnose is a destructive disease of cool-season putting green turf caused by the fungal organism Colletotrichum cereale (formerly C. graminicola). Colletotrichum cereale infects turf when plants are weakened by physiological or mechanical stresses. Anthracnose incidence and severity have increased throughout the southern United States over the past 15 years. The proliferation of this disease may be due to the intense management practices performed on putting greens such as decreased mowing heights, reduced irrigation and minimal nitrogen fertilization to increase green speeds. Diagnosticians have improved their ability to recognize C. cereale structures, resulting in the trend of increased disease identification frequency.
Colletotrichum cereale infects leaf, crown, stolon or root tissues of creeping bentgrass (Agrostis stolonifera) or annual bluegrass (Poa annua), but it is normally more severe on annual bluegrass. Anthracnose is characterized by the portion of the plant the fungus infects resulting in foliar blight or basal (stem) rot. Host specificity has been identified in C. cereale isolates, meaning that infection of creeping bentgrass or annual bluegrass will be more severe in mixed turfgrass stands depending on host preference.
Foliar Blight. These symptoms are predominantly observed on creeping bentgrass putting greens during the summer with the onset of heat stress but may occur on annual bluegrass putting greens. Foliar blight symptoms in the turf include large, irregularly shaped patches lacking turf density and appearing yellow to bronze (Figure 1). Initially, leaf symptoms occur on older leaves near the base of the plant but progress to younger leaves (Figure 2). Leaves infected by C. cereale exhibit chlorosis (yellowing) at the tip of the leaf that moves downward, eventually becoming necrotic (Young et al., 2008).
Basal Rot. These symptoms are generally observed on annual bluegrass putting greens but may also be observed on creeping bentgrass greens as well. This disease differs from foliar blight in that basal rot may occur throughout the year. Turf symptoms are initially 0.25- to 0.5-inch diameter spots appearing orange to bronze. As the fungus begins infecting crown and stem material, the patches will enlarge and coalesce but remain sporadic throughout the symptomatic area. As stems and crowns are infected by the pathogen, the symptoms of these tissues progress from a water-soaked appearance to black, rotted tissue (Figure 3). Leaf symptoms on annual bluegrass and creeping bentgrass are similar to foliar blight symptoms, with the older leaves initially becoming chlorotic and progressing to younger leaves (Smiley et al., 2005).