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  • Author or Editor: Keith J. Karnok x
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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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Abstract

The morphological progression of low-temperature discoloration as affected by gibberellic acid (GA3) applied exogenously was determined for ‘Ormond’ (chill-tolerant) and ‘Tee Dee’ (chill-sensitive) bermudagrass [Cynodon dactylon (L.) Pers.] and ‘Floratam’ (chill-tolerant) and ‘Texas Common’ (chill-sensitive) St. Augustinegrass [Stenotaphrum secundatum (Walt) Kuntze] while exposed to chilling temperatures of 7°C (day)/5° (night) for 14 days. Visible symptoms on all cultivars occurred first and progressed most rapidly on horizontal leaf blades and stems which were directly exposed to light. Leaf blades and stems deep in the canopy or shaded by other plant parts were the last to show injury. Bleaching and/or the formation of a purple pigmentation occurred in the leaf blades and stems of both bermudagrass cultivars within 3 days of chilling stress. The symptoms occurred first and proceeded more rapidly on ‘Tee Dee’. Both St. Augustinegrass cultivars showed visual symptoms after 5 or more days of chilling stress. Wilting was followed immediately by the development of water-soaked lesions and finally by total necrosis. The application of GA3 at 62.5 g ha-1 stimulated shoot growth of both chill-stressed bermudagrass cultivars and almost completely prevented development of a purple pigmentation in the leaf blades and stems. GA3 did not stimulate shoot growth, and it increased the rapidity and severity of the chilling-injury symptom development on the blades and stems of both St. Augustinegrass cultivars, indicating a possible toxicity effect at the rate used.

Open Access

Abstract

A creeping bentgrass (Agrostis palustris Huds. ‘Penncross’) green was treated with the herbicide ethofumesate at single and sequential applications during 2 years. A single ethofumesate application in September at 1.1, 1.7, or 2.2 kg a.i./ha slightly discolored bentgrass, but turfgrass quality was not significantly reduced. With October treatments, discoloration increased at 1.7 and 2.2 kg a.i./ha, but not at 1.1 kg. Ethofumesate treatments made in September and October resulted in less discoloration and reduced quality less than with applications made in October and November. Bentgrass treated in October and November was severely injured in 1 of 2 years, but turfgrass fully recovered by the following spring with no stand loss. Chemical names used: (±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranylmethanesulfonate(ethofumesate).

Open Access

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.

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Abstract

Nondestructive studies of plant root systems are limited to hydroponic and glass-wall-type growing systems, which are expensive and limit the ways to observe and measure root structures. The following system was adapted from agronomic studies as a convenient, cost-efficient, and sensitive method of monitoring root growth of horticultural crops.

Open Access