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John C. Pair

In 1983, a trial was initiated to compare numerous selections of sugar maple (Acer saccharum) for adaptability to stressful conditions in south central Kansas (zone 6). Included were seedlings of Caddo maple, a southern ecotype, collected from a population native to central Oklahoma. Selected trees have shown superior resistance to scorch and leaf tatter compared to cultivars in the trade. Pre-dawn measurements indicated higher xylem water potential than `Green Mountain' and `Fairview' under drought stress. Leaf emergence of Caddo maples has been earlier in the spring, and fall color develops later than other sugar maples. Propagation of potential cultivars with early fall color has been principally by T-budding on Caddo understock in July and August, although side-veneer grafting in winter has been successful. In addition to superior summer leaf quality, growth in caliper and total height has been greater than other A. saccharum cultivars.

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John C. Pair

Lepidote and Elepidote Rhododendron cultivars were established May 2, 1988 in selected landscape sites with amended soil to evaluate performance under stress by the continental climate characterized by hot summers and cold, desicatting winters. Evergreen azaleas were also screened with emphasis on flower bud hardiness. Survival and flowering were acceptable in exposures protected from winter sun especially on Lepidote `PJM Victor' which survived 42°C although Phytophthora root rot occurred in hottest locations. In contrast flower buds on large leaf types `Nova Zembla' and `Roseum Elegans' often failed to open due to desiccating winter conditions. Cultivars which flowered best after 3 years were `Aglo', `Lodestar', `Nova Zembla', `Olga Mezitt', `PJM', `Waltham' and `Windbeam'. Hardiest azaleas which flowered following -28°c were `Boudoir', `Caroline Gable', Kaempferi `Herbert', poukhanense `Karens', `Pride's Pink' and `Snowball'. Additional cultivars appear promising given suitable bed preparation, proper exposure and adequate maintenance in spite of climatic extremes in the great plains.

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John C. Pair

Since 1974, numerous species and cultivars of evergreen azaleas have been evaluated for hardiness and adaptability to south central Kansas (zone 6). Selections included Kurumes, Gable hybrids, Shammarello hybrids and others in various amended beds and in several landscape exposures. Hardiest cultivars include `Boudoir', `Caroline Gable', `Herbert', `Karens', `Pride's Pink', `Purple Splendor', and `Snowball' which flowered following -18F (-28C). Moderately hardy were `Elsie Lee', `Holland', `Girard Roberta' and `James Gable'. Best hardiness was found in cultivars and hybrids with Rhododendron kaempferi, and R. yedoense var. poukhanense parentage. Plants in soil amended with sphagnum peat moss or peat plus sulfur were superior to those in soil containing cotton burrs. Winter shade proved valuable in providing the best landscape site and northeast was generally better than a northwest exposure.

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Houchang Khatamian and John C. Pair

Softwood cuttings of `Commemoration' and two selections of Caddo maple (83-NR3 and 90-7185) were collected on 24 May 1995 from specimen trees located at the Wichita Horticultural Research Center. Uniform cuttings 14–19 cm long containing 4–5 leaves were dipped in selected IBA hormone solutions for 10 seconds and stuck in a rooting mix consisting of 30% Canadian sphagnum peat and 70% perlite (v/v). The experiment was conducted in a greenhouse located at Kansas State Univ. To achieve a high relative humidity around the cuttings, a fog generator (Humidifan, turbo XE 1000) was installed and operated for 12 hours per day. The experiment was a factorial design with 3 maple selections, 4 hormone concentrations and 3 replications. After 10 weeks cuttings were evaluated for rooting using a visual rating scale of 1–5. There was a significant difference between the maple cultivars and the IBA levels tested. `Commemoration' cuttings rooted the best among the maple cultivars with all of the IBA treatments. The best rooting of Caddo maple selection (83-NR3) took place with 10,000 ppm IBA. None of the cuttings of the other Caddo maple selection (90-7185) rooted regardless of the hormone concentration. The rooted cuttings were potted in 15 cm plastic containers filled with Metro Mix 702 for future production.

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Houchang Khatamian and John C. Pair

Softwood cuttings of Acer saccharum `Commemoration', a Caddo maple selection (90-7185), and Acer truncatum were collected on 12 July 1996 from specimen trees at the Wichita Hort. Res. Center. Ten uniform cuttings of 14to 19cm-long containing four to five leaves were dipped for 10 sec in 0, 5000, 10,000, 15,000, or 20,000 ppm IBA solution and Hormodin™ #2. Cuttings were rooted in a mix of 30% Canadian sphagnum peat and 70% perlite (v/v) and placed in a greenhouse located at Kansas State Univ. The greenhouse was equipped with a fog generator (Humidifan, turbo XE 1000) that was operated for 12 hr/day from 12 July to 5 Oct. 1996. After 12 weeks, cuttings were evaluated for rooting quality and percent using a visual rating scale of 1–5. `Commemoration' rooted with all IBA treatments. The control treatment resulted in a 100% rooting, whereas the rooting with 5000 or 10,000 ppm IBA and or Hormodin™ #2 was 90%. Caddo maple (90-7185) rooted at 89% with control treatment, followed by 78% and 67% with 10,000 ppm IBA and Hormodin™ #2, respectively. As reported previously, none of the cuttings of this maple, collected on 24 May 1995, had rooted, regardless of hormone treatment. The best rooting for Acer xtruncatum was 90% with 5000 ppm IBA and 80% with control and Hormodin™ #2, respectively.

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Alice Le Duc and John C. Pair

Five cultivars of boxwood (Buxus microphylla)—'Winter Gem', B. microphylla var. japonica `Green Beauty', `Green Velvet', `Green Mountain' and `Glencoe'—were planted in twelve different exposures at Manhattan and Wichita, Kan., representing USDA hardiness zones 5 and 6 respectively. The 1995–96 winter was one of great extremes. Lows of –25°C for Manhattan and -23°C for Wichita were recorded, along with sharp 24-hour temperature drops of 31–32°C in January and March. Differences in cultivar performance were noted between the sites. At the Wichita site best winter color was exhibited by `Green Velvet' and `Glencoe', whereas `Green Mountain' sustained some bronzing of foliage due to winter sun. At Manhattan only `Glencoe' in protected locations exhibited good winter color. All other surviving cultivars showed considerable bronzing. In addition, `Green Beauty' was severely damaged at Manhattan, sustaining bark splitting due to low temperatures, although most plants survived at Wichita. Shaded locations on north, northeast and northwest produced best plant quality of all cultivars; whereas, the poorest plant performance occurred on south and southeast exposures.

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John C. Pair, Channa Rajashekar and Michael Shelton

Numerous cultivars of lacebark elm (Ulmus parvifolia) have been introduced recently without adequate testing of their hardiness. A block of commercial cultivars plus numerous experimental numbers were established to observe differences in growth form, ornamental characteristics, and cold hardiness. Laboratory freezing tests were conducted from November to March over a 3-year period to determine acclimation and deacclimation to low temperatures. Stem sections approximately 5 cm long were sealed in test tubes and placed in a low-temperature programmable freezer maintained at 0°C. Samples were cooled by approximately 6°C per hour from 0 to –48°C and held for 1 h at each temperature. Samples were then removed, allowed to thaw at room temperature, and held for 7 to 10 days. Stem samples were sectioned longitudinally to observe browning in xylem and bark tissues. During the winter of 1995–96, no visible injury could be noted on trees in the field in spite of very dry, desiccating weather with temperatures reaching –23°C. Laboratory freezing tests indicated acclimation to –30°C by 18 Dec. 1995 on several cultivars. During warm periods in February, deacclimation occurred on many selections to –18°C, whereas others maintained a killing point of –30°C. Growth form, bark exfoliation, and fall color varied among cultivars.

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Alice Le Duc and John C. Pair

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Steve C. Yuza, Art L. Youngman and John C. Pair

This study examined physical factors and physiological responses of five different ecotypes and cultivars of Acer saccharum and A. nigrum. The objective was to determine variations in leaf conductance and xylem water potential and correlations associated with their natural geographic distribution. Compared were two ecotypes of sugar maple, Caddo and Wichita Mountains, native to Oklahoma with cultivars Green Mountain and Legacy, plus black maple seedlings from Iowa. Measurements taken included leaf conductance, xylem water potential and soil water potential in a replicated block of 15-year-old trees. The two ecotypes had consistently higher photosynthetic rates, stomatal conductance and transpiration rates than other selections. Xylem water potentials were significantly higher for Caddo maples than Green Mountain, Legacy and Acer nigrum in both predawn and midday samples. This difference in water availability can be associated with a tendency for Caddo to vary its stomatal conductance. The other tree types maintained stable stomatal conductances.

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Jason J. Griffin, Houchang Khatamian, John C. Pair and Mike Shelton