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Ursula K. Schuch

A two-part exercise was developed as part of the horticulture curriculum at Iowa State University to familiarize students with the American Standard for Nursery Stock (ASNS), and to allow them to practice and apply the ASNS with a variety of categories and types of ornamental plants. The first part of the exercise requires students to determine, according to ASNS standards, appropriate root ball/container size for plants to be moved from an existing immature landscape. During the second part, students evaluate whether root ball or container size of plants in a nursery is appropriate for the plant shoot dimensions. The exercise was designed for students to work in informal groups in a cooperative learning environment.

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Ursula K. Schuch

Several large cities in the southwestern United States have set a target to increase their tree canopy cover up to 25%, which often requires more than doubling the current canopy cover. A major goal is to alleviate high temperatures and support public health in addition to gaining all the other benefits conferred by urban forests. Rising temperatures, the arid climate, continued drought, increasing population numbers, and the growing urban forest in the southwestern United States fuel the demand for more water. Using water wisely to garner the benefits of trees requires the application of sufficient irrigation based on the water needs of different species. Current irrigation recommendations for trees are often based on expert consensus. Research-based results of tree irrigation studies from the southwestern United States are presented to give specific examples of how trees respond when they are exposed to different irrigation regimes.

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Ursula K. Schuch

Eight-week-old potted chrysanthemum (Dendranthema grandiflora Tzvelev. c. Ovaro) plants were treated with a soil drench of 0 or 2.5 mg uniconazole per liter and irrigated daily with 350 or 250 ml of nutrient solution. Plants were frequently water-stressed during their development. At the beginning of anthesis treatments were split and transferred to chambers with 20C/24 hr photoperiod or 25C/dark conditions. Anthesis progressed at the same rate in the two postharvest storage conditions, regardless of previous treatments. Plants were not watered until wilting, which was observed first in control plants under continuous photoperiod (8 days) and last in uniconazole-treated plants in dark storage (12 days). During the first 6 days in storage, evapotranspiration (ET) was lower for plants grown with 250 ml daily irrigation. From day 8 to day 12, when most plants were irrigated after they had wilted, ET was affected by uniconazole and an interaction of uniconazole and storage conditions.

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Ursula K. Schuch and Barbara Biernacka

Four azalea cultivars [Rhododendron × `White Lace' (WT), `Southern Charm' (SC), `Formosa' (F), and `George Tabor' (GT)] with different growth and flowering habits were treated with a foliar spray of uniconazole (U) at 0, 10, or 15 mg·liter–1 with or without a surfactant. GA was applied at 0 or 15 mg·liter–1 as a foliar spray to half of the plants on 23 Sept. 1993, 53 days after the uniconazole application. U reduced number, length, and dry weight of bypass shoots, and increased number of flower buds for all cultivars by Dec. 1993. Application of GA after U further increased the number of flower buds on SC and GT, which otherwise had few flowers. At the final evaluation in Mar. 1994, time to anthesis for cultivars F and GT was not affected by any treatment. Anthesis of SC and WL treated with 15 mg U and GA/liter started 6 days earlier than those treated with 15 mg U/liter. Number of flowers at anthesis and number of flower buds was increased two to four times on U-treated vs. nontreated plants. U decreased plant height, size, leaf area, and shoot dry weight of all cultivars. Shoot elongation of F and GT was further reduced with the 15 vs. 10 mg U/liter treatment. Application of GA increased the retarding effects of U on plant height for WL, SC, and GT, and on leaf area and shoot dry weight for WL.

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Kathryn S. Hahne and Ursula K. Schuch*

The objective of this study was to determine whether mesquite (Prosopis velutina) seedlings have a preference for the ammonia or nitrate form of nitrogen (N), and to determine the optimum rate of N to maximize growth and minimize N leaching when seedlings are grown in different substrates. Mesquite seedlings were fertigated with different ratios of NH4 +: NO3 - to determine effects on shoot and root growth and N-uptake efficiency. Nutrient solution containing 67% NH4 + : 33% NO3 - resulted in greatest biomass after 120 days of fertigation. N leachate remained stable until 12 weeks after the onset of treatment, but increased significantly by week 16. Subsequently, mesquite seedlings were grown in sand or soilless media and were fertigated with a solution of 67 % NH4 +: 33% NO3 - at a rate of 25, 50, 100, or 200 mg·L-1 of N. After 60 days, plants in media produced 41% more leaves and total biomass compared to those in sand. Leaf number was greatest for plants grown at 200 mg·L-1 of N in both substrates. Root biomass of plants in media showed no response to increasing N concentrations while root biomass of seedlings in sand were similar for the three lower N concentrations and nearly doubled for the highest one. Shoot biomass of seedlings receiving 25, 50, or 100 mg·L-1 of N was similar, but more than doubled for plants fertigated with 200 mg·L-1 of N. N leachate losses were highest from seedlings growing in sand and receiving the two higher N fertigations, those in media had greatest N leachate loss when fertigated at 200 mg·L-1 of N. For balanced mesquite seedling growth and minimum N leaching losses, concentrations between 50 to 100 mg·L-1 of N are recommended. Implications of using a sand culture system vs. soilless growing substrate for nutrition studies will be discussed.

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H. Brent Pemberton* and Ursula K. Schuch

Rose (Rosa sp.) cultivars Blue Girl and Mister Lincoln were harvested bare-root on 1 Nov. 2001 and 22 Nov. 2002 from a commercial nursery in Arizona. Grade 1 plants were then potted and forced to flowering in either Tucson, Ariz., or Tyler, Texas. Total chilling hours were calculated as the number of hours that the plants were exposed to a temperature below 7 °C in the field and during shipping and cold storage. Data were recorded when the petals on the first flower beg an to reflex. Overall, the number of flowering shoots and plant performance was positively correlated to digging date, weeks of cold and total chilling hours received. Days from potting to flower were negatively correlated to weeks of cold storage and chilling hours. However, when the data were separated by location, the number of flowering shoots, the percentage flowering shoots, and plant performance was positively correlated to weeks of cold and chilling hours in Arizona, but was positively correlated to digging date in Texas. Days from potting to first leaf unfolding were recorded in Arizona only and were negatively correlated to weeks of cold storage and chilling hours. Days from potting to flower were negatively correlated to chilling hours at both locations and also to weeks of cold storage in Texas. The increase in chilling from two or four weeks of cold storage increased the number of flowering shoots and performance rating of plants forced in Arizona during both seasons, but only for the 2001 season in Texas. During the 2002 season in Texas, these responses were not influenced by cold storage, but were greater than those seen during the 2001 season. In Arizona, days from potting to flower were greater in 2001 than 2002, and decreased in response to cold storage in 2001, but not in 2002.

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Darren L. Haver and Ursula K. Schuch

Salt-sensitive (`Illusion') and salt-tolerant (`Blazon') New Guinea impatiens cultivars were grown for 70 days with a controlled-release fertilizer at 3.3, 6.6, or 9.9 g/pot under constant media moisture of 1–3 kPa or 4–6 kPa. Optimum growth for both cultivars occurred using 6.6 g/pot and a media moisture level of 1–3 kPa. The leaf area (LA), leaf number (LN), leaf dry weight (LDW), stem dry weight (SDW), and root dry weight (RDW) were significantly reduced at 9.9 g/pot in `Illusion', with values similar to those at 3.3 g/pot. LDW, SDW, RDW, LA, and LN were similar for 6.6 g/pot and 9.9 g/pot in `Blazon'. At 4–6 kPa LDW, SDW, RDW, LA, and LN decreased from low to high in `Illusion'. LA in `Blazon' also decreased from low to high, but LDW, SDW, RDW, and LN were unaffected. Media EC levels were greater in the upper half of the media regardless of moisture level. EC values as high as 7.3 dS·m–1 in the upper half of the media and as high as 5.2 dS·m–1 in the lower half of the media were measured without causing plant mortality.

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John F. Karlik and Ursula K. Schuch

Moisture loss from bare-root plants during postharvest handling and storage can have a significant effect on plant growth and survival during establishment. Three film-forming antitranspirants and hot wax were applied to bare-root roses packaged after harvesting from the field and before three months of cold storage to determine effects on vegetative growth and flowering. Subsequently, during three weeks under display conditions, plants treated with hot wax resumed growth at the fastest rate compared to control or antitranspirant treatments. Hot wax-treated plants continued to grow at a faster rate than the other plants for two weeks following transplanting in the field. For the remaining 10 weeks of the experiment no differences in vegetative growth or flowering development were found between treatments. Over 70% of the plants treated with hot wax became sunburned, resulting in severe cane damage and plant dieback. Less than 20% of the plants from the other treatments were damaged.

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Kathryn S. Hahne and Ursula K. Schuch

Velvet mesquite [Prosopis velutina Woot., Syn.: P. juliflora (Swartz) DC. var. velutina (Woot.) Sarg.] has become more popular in arid landscapes of the southwestern U.S., but little information on N requirements during the seedling stage is available. In addition to optimize growth of seedlings, minimizing N in runoff during production is an important consideration. Experiments were conducted to determine how biomass production and N leaching were affected first by different ratios of ammonium and nitrate N in sand culture and second by different N concentrations when seedlings were grown in two substrates. Mesquite seedlings produced the greatest biomass after 120 days when fertigated with a solution of 33 NO3 : 67 NH4 +. Loss of N through leachate was 40% greater when NH + 4 comprised two thirds or more compared to one third or none in the fertigation solution. Nitrogen in leachate was highest after 16 weeks of treatment, coinciding with the reduced growth rate of seedlings. The second experiment utilized either sand or commercial growing media and a fertigation solution of 33 NO3 : 67 NH4 +. Fertigation with 200 mg·L–1 N after 60 days in either substrate produced greatest biomass, while rates of 25, 50, or 100 mg·L–1 N produced about half of that biomass. With few exceptions, less N in either form was found in leachate when seedlings were grown in media and were fertigated with the two higher N rates compared to seedlings grown in sand at the two higher N rates. Plant morphology, biomass accumulation, photosynthate allocation, and the fate of N in the growing substrate and in leachate were strongly affected by the choice of growing substrate.

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Kristen Hanson, Tilak Mahato, and Ursula K. Schuch

High tunnels are unheated structures covered with polyethylene (PE) glazing to protect high-value crops from adverse weather. The objective of this study was to raise soil temperatures to determine the efficacy of soil solarization using clear mulch on the soil surface and glazing or no glazing on a high tunnel during the hottest months of the year in the semiarid southwestern United States. Solarization trials were conducted in May and June 2013 in two high tunnels in southern Arizona. Highest soil temperatures were reached with the combination of a high tunnel covered with glazing and the soil covered with PE mulch. Average daily soil temperatures were 48 and 47 °C and average degree hours (DH) per day (base temperature 45 °C) were over 14 at soil depths of 5 and 15 cm. The average daily maximum soil temperature at 5- and 15-cm depth was 63.4 and 52 °C, respectively. The second highest soil temperatures were reached when the soil was covered with PE mulch without high tunnel glazing, which resulted per day in 5.2 DH above 45 °C at 5 cm and less than one DH at 15-cm depth. Glazing on the high tunnel without covering the soil surface raised soil temperatures only at the 5-cm depth above 45 °C, but not further down. High tunnel producers in the low desert areas in the southwestern United States can complete solarization in less than 1 week, depending on the organism to be controlled, when the soil is fallow during the summer months with glazing on the high tunnel and on the soil surface.