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John H. Dunn, Erik H. Ervin, and Brad S. Fresenburg

Various mixtures of tall fescue, Festuca arundinacea Schreb., Kentucky bluegrass, Poa pratensis L., and perennial ryegrass, Lolium perenne L., may be beneficial for turf culture because of genetic diversity and improved tolerance to environmental stresses compared with a single species. Turf-type tall fescue, dwarf tall fescue, Kentucky bluegrass, and perennial ryegrass were seeded as cultivar blends and in all possible combinations as species mixtures in two locations, irrigated and nonirrigated. Turf was mowed at 19 and 51 mm and subjected to an interval of brief, but intensive, simulated traffic. Perennial ryegrass was the dominant species in all mixtures with tall fescue, Kentucky bluegrass, or both. After 5 years, turf-type tall fescue comprised 62% of mixtures with Kentucky bluegrass when averaged over locations. Dwarf tall fescue comprised 48% of mixtures compared with Kentucky bluegrass at 44%. Kentucky bluegrass was more competitive with tall fescue in the irrigated vs. nonirrigated location. Mowing height effected small changes in populations year to year while simulated traffic had little effect on populations at 1 year following treatment. The advantage of mixing species compared with individual species to reduce disease occurrence was evident on several occasions. Our study supports earlier research reports that tall fescue will remain competitive in mixture with Kentucky bluegrass several years after seeding.

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Michele R. Warmund, Rusty Fuller, and John H. Dunn

Rhizomes of `Meyer' zoysiagrass (Zoysia japonica Steud.) were subjected to temperatures below 0 °C and were subsequently placed in a growth chamber with air at 34 °C day/28 °C night to determine the rate of shoot growth from nodes. Rhizomes exposed to subzero temperatures produced shoots steadily up to 16 days after freezing (DAF), but subsequent shoot growth from rhizomes was minimal. At 32 DAF, shoots were present on 68% and 44% of the nodes of unfrozen control (2 °C) rhizomes and those frozen to -7 °C, respectively. In another study, samples were frozen to a sublethal temperature (-7 °C) to examine the distribution of extracellular ice voids near the apical meristems of rhizomes and to characterize tissue recovery. Extracellular voids were present within the leaf tissue and between the leaves in samples prepared for scanning electron microscopy (SEM) immediately after freezing to -7 °C. By 12 DAF, most of the remaining voids were observed in older leaves. Nearly all extracellular voids in the leaves were absent by 20 DAF. However, by 28 DAF, some rhizomes still had small voids between leaves. Although the structure of zoysiagrass rhizomes subjected to -7 °C was temporarily disrupted, tissues recovered from extracellular freezing and new shoot growth was produced following exposure to warm temperatures.

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Russell L. Fuller, Michele R. Warmund, John H. Dunn, and Suleiman S. Bughrara

Zoysiagrass rhizomes were sampled at various intervals, from October through March, to determine their susceptibility to low-temperature injury. Five-node rhizome sections of the following genotypes were subjected to sub-freezing temperatures at each date: `Belair', `DAL 8507', `El Toro', `Emerald', `Korean Common', and `Meyer'. Rhizome sections of each cultivar were wrapped in moistened cheesecloth, enclosed in aluminum foil, and placed in a freezing chamber at –2C. After 2 h at –2C, samples then were cooled at 1C/h to temperatures estimated to result in tissue injury. Fifteen rhizomes of each genotype were removed from the chamber at each test temperature. After thawing for 12 h, rhizomes were planted and regrown in a growth chamber at 34C day/28C night for 4 weeks. In the freezing test conducted on 12 Oct. 1994, rhizomes of `Meyer' and `Emerald' had greater shoot regrowth than those of `El Toro' after exposure to –6C. The only rhizomes that produced shoot growth after exposure to –8C were those of `Korean common', `Meyer' and `Belair'.