Microbial Populations and Suppression of Dollar Spot Disease in Creeping Bentgrass with Inorganic and Organic Amendments. L. X. LIU, Postdoctoral Research Associate, University of Guelph, Guelph, Ontario, NIG 2W1. T. HSIANG, Assistant Professor, Department of Environmental Biology, K. CAREY, Associate Director, Guelph Turfgrass Institute, and J. L. EGGENS, Professor, Department of Horti-cultural Science, University of Guelph, Guelph, Ontario, NIG 2W1. Plant Dis. 79:144-147. Accepted for publication 6 October 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0144.

Alginate, ammonium nitrate, Bovamura, Milorganite, Ringer Lawn Restore, Ringer Greens Super, Ringer Turf Restore, Sandaid, sewage sludge and sulphur-coated urea were evaluated from 1991 to 1993 on a creeping bentgrass (Agroslis paluslhs) green and a Kentucky bluegrass (Poa pratensis) lawn for their effects on soil bacterial and fungal populations and dollar spot disease incidence. Over the 3 yr, fertilizers were applied every 4 wk at recommended rates from early June to September, and once again in November. Application of Ringer fertilizers, ammonium nitrate, and sulfur-coated urea gave rise to significantly higher microbial populations on turfgrass leaves and in thatch and soil than did most other fertilizers. In most experiments, Ringer fertilizers also improved water retention in thatch compared with other treatments. Ringer Greens Super, Ringer Turf Restore, or ammonium nitrate on the creeping bentgrass green significantly suppressed dollar spot disease compared with the other amendments or the untreated control, but for most of the season they did not control disease as well as the fungicide chlorothalonil did.