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Keith J. Karnok and Kevin A. Tucker

Localized dry spot (LDS) caused by water repellent soil is a common problem on golf course putting greens having a predominately sand root zone. Fairy ring often causes LDS by developing hydrophobic soil. Although the fungicide flutolanil is labeled for the control of fairy ring, golf course superintendents often apply flutolanil to all LDS caused by hydrophobic soil and other conditions. The objective of this study was to determine the effect of flutolanil on an existing hydrophobic soil. The study was conducted on a creeping bentgrass [Agrostis palustris (synonym A. stolonifera)] experimental golf green in which the top 4 inches (10.2 cm) of the root zone was a moderately hydrophobic sand. Six treatments were used: uncored, cored, flutolanil (two applications.), flutolanil + Primer wetting agent (two applications.), Primer (two applications.) and Primer (three applications.). Plots receiving the fungicide and wetting agent treatments were cored before application. Each treatment containing the wetting agent significantly reduced soil water repellency. Flutolanil without wetting agent had no effect on soil hydrophobicity.

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Maxim J. Schlossberg, Keith J. Karnok and Gil Landry Jr.

Subjection of intensively managed creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds.). Farw., (syn. Agrostis palustris Huds.)] to supraoptimal soil temperatures is deleterious to root viability and longevity. The ability to estimate viable root length would enable creeping bentgrass managers to more accurately schedule certain management practices. The purpose of this rhizotron study was to develop a model, based on an accumulated degree-day (ADD) method, capable of estimating viable root length density of established `Crenshaw' and `L93' creeping bentgrass maintained under putting green conditions. Viable root length density observations were made biweekly and soil temperature data collected April through September 1997, and January through August 1998 and 1999. Relative viable root length density (RVRLD) is defined as the measured viable root length density divided by the maximum density attained that spring. In both years, maximum annual viable root length density for all plots was reached, on average, by 138 days from the beginning of the year (18 May). Cultivar and year effects were nonsignificant (P = 0.67 and 0.20, respectively). Degree-day heat units were calculated using an array of base temperatures by integral and arithmetical methods. Although the two accumulative methods proved suitable, the model regressing arithmetical degree-day accumulations against the bentgrass RVRLD provided a better fit to the data set. Use of the 10 °C base temperature in the arithmetical ADD calculations provided the following model; RVRLD = 0.98 - [1.30 × 10-4 (ADD)], accounting for 83.8% of the experimental variability (P < 0.0001). As several abiotic/edaphic factors have been shown to significantly influence root growth and viability, development of a widely usable model would include additional factors.