Defines Dead Spot More Clearly

In 1998, researchers at the University of Maryland discovered a new disease of creeping bentgrass caused by an unidentified species of Ophiosphaerella. Through morphological and molecular study, it was shown that the pathogen constituted a new species, Ophiosphaerella agrostis, and the disease was named bentgrass dead spot. Subsequently, O. agrostis was found in Texas and Florida causing dead spots in hybrid bermudagrass greens. The disease is now referred to as dead spot. In creeping bentgrass grown on putting greens, dead spot appears initially as small, dime-sized spots that may increase up to 3 inches to 4 inches in diameter. During early stages of disease development, the spots are reddish-brown and often are confused with other turfgrass diseases such as dollar spot, copper spot and microdochium patch. Spots also may be mistaken for damage from black cutworms or ballmarks, which commonly are found on putting greens. In the later stages of dead spot development, grass in the center of the spots becomes tan, while leaves in the outer edge appear reddish-brown. Patches may be distributed throughout the putting green or localized, and generally do not coalesce. Spots often form depressions or pits and may severely reduce the quality and playability of the putting surface. Active dead spot infection centers generally appear in areas with full sun and good air circulation. Initially, O. agrostis infection centers occur predominantly along ridges, on mounds and south-facing slopes of greens. These areas generally are associated with higher soil temperatures and often are the first to exhibit drought symptoms. The aforementioned conditions generally result in higher levels of plant stress and may reduce the defense capabilities of bentgrass plants. Dead spot only has been found on newly constructed greens or on older greens that were fumigated with methyl bromide. The disease generally develops within one to two years of establishment, but outbreaks have been observed in creeping bentgrass greens less than 1 year old and as old as 6. With few exceptions, dead spot is most severe during the first year of symptom Continued on page 60 Among commercial creeping bentgrass cultivars, dead spot generally was most severe in L-93, Penn A-1, A-4, G-1,G-6, Imperial and Providence. IN THIS ISSUE