Mowing practices to reduce dollar spot disease on creeping bentgrass and environmental influences on the aggressiveness of Sclerotinia homoeocarpa

The influence of mowing time, mower blade sharpness, mowing frequency, and squeegee dew removal on dollar spot (DS) incidence was determined in a two year field study on 'Penncross' creeping bentgrass mowed at 16 mm. Leaf wetness duration (LWD) effects on DS were ascertained in a controlled environment study by exposing pots of Penncross creeping bentgrass to repeated cycles of 6, 12 or 18 h of leaf wetness after inoculation with S. homoeocarpa . This study provides evidence that DS infections can occur with repeated cycles of 6 h of LWD. Mowing study data indicate DS could be better managed by reducing LWD to a minimum. In this study daily dew removal at 0400 h was most effective in DS reduction followed by dew removal at 2200 h, and 1000 h, respectively.; In a second study, the influence of temperature on growth rate and aggressiveness of fifteen S. homoeocarpa isolates was investigated in a controlled environment. To determine growth rate, isolates were grown on potato dextrose agar (PDA) at temperatures of 5, 10, 15, 20, 25, and 30° C. Aggressiveness of isolates was assessed by inoculating pots of Penncross creeping bentgrass with S. homoeocarpa isolates and placing them in polyethylene bags at 5, 10, 15, 20, 25, and 30° C for one week. Significant variation between growth rate and aggressiveness of isolates occurred at all temperatures. In addition, DS symptoms developed consistently at 10° C, a significantly lower temperature than has been previously reported.; Studies of creeping bentgrass guttation fluids and dew collected from creeping bentgrass were also conducted. The growth of S. homoeocarpa in dew collected from three cultivars of creeping bentgrass ('Crenshaw', 'Penncross', and 'L-93') was investigated. Dew from 'Crenshaw' promoted the greatest growth of S. homoeocarpa mycelium in vitro . Dew from 'Penncross' was intermediate in supporting S. homoeocarpa growth, and dew from 'L-93' was least supportive of growth. Interestingly, the susceptibility of each of these creeping bentgrass cultivars to DS follows the same pattern with 'Crenshaw' being most susceptible, 'Penncross' being less susceptible and 'L-93' being the least susceptible to dollar spot.