Twelve species of woody ornamentals were grown in containers in Riverside and Davis, Calif., to determine plant water use and compare crop coefficients (Kc) calculated with reference evapotranspiration (ET) from local weather stations (ETcim) or atmometers (ETatm). Water use, Kcatm, and Kccim differed by species, location, and month of the year. Raphiolepis indica (L.) Lindl., Pittosporum tobira (Thunb.) Ait., Juniperus sabina L., and Photinia ×fraseri Dress. were the highest water users in Riverside and Arctostaphylos densiflora M.S. Bak., Juniperus, Cercis occidentalis Torr., and Pittosporum used the highest amount of water in Davis, when averaged over the 20-month study period. Rhamnus californica Eschsch., Prunus ilicifolia (Nutt.) Walp., and Cercocarpus minutiflorus Abrams. were among the lowest water users in both locations. Although plant water use fluctuated considerably between individual sampling dates, the relative ranking of species water use in each location changed very little over the study period. During periods of high winds, ETcim may not provide an accurate reference for container crops. Kc values fluctuated seasonally from as much as 1 to 4.7 for high water users, while values were stable for low water users and also for Buxus microphylla japonica Rehd. & E.H. Wils., an intermediate water user. During periods of low ET, especially in fall and winter, Kc values were artificially high and failed to correspond to the plants' low water use. Kc values for low water users seem to be useful to estimate water requirements over an extended period of time, whereas general Kc values seem to have limited value for plants with high water demand and need to be modified for different growth stages and growing locations.
Ursula K. Schuch and David W. Burger
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.
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.
John F. Karlik, J. Ole Becker, and Ursula K. Schuch
The impending worldwide restrictions on the use of methyl bromide (MeBr) as a soil fumigant have prompted an intensive search for more-effective methods for delivering MeBr or replacement compounds. Although the majority of agrochemicals are applied in the solid phase or the liquid phase at ambient pressure and temperature, some chemicals, including certain soil fumigants such as MeBr, are gases under normal field conditions. Experiments were conducted to evaluate use of two types of commercial drip irrigation tubing to deliver gases to nontarped planting beds. Air moved through each tubing type immediately after burial; water was not necessary for inflation. Air was also able to move through 40 m of buried rigid drip tubing and through 90 m of buried flat tape that had been used for subsurface drip irrigation for more than 1 year. Mixtures of known ratios of propane and air were introduced into the buried tubing over several time intervals to evaluate gas movement from buried drip tubing into the surrounding soil matrix. Samples were collected from sets of three soil gas sampling tubes placed 15, 30, and 45 cm to the side of the buried tubing and at regular intervals along the length of the tubing, and propane concentrations were quantified by gas chromatography. Tubing lengths and run times affected the magnitudes and uniformity of propane concentrations. Results suggest gas-phase chemicals can be delivered via buried drip-irrigation tubing, but effective distances from the point of introduction will be limited by the low densities and viscosities of gases, and corresponding high rates of escape through tubing emitters.
Ursula K. Schuch, Anita N. Miller, and Leslie H. Fuchigami
Dormant coffee (Coffea arabica L.) flower buds require water stress to stimulate regrowth. A xylem specific watersoluble dye, azosulfamide, was used to quantify the uptake of water by buds after their release from dormancy by withholding water. In non-stressed flower buds, the rate of water uptake was generally slower and variable. In stressed flower buds, the rate of uptake tripled from one day to 3 days after rewatering and preceded the doubling of fresh and dry weight of buds. Free, ester, and amide IAA levels of developing flower buds were measured by GCMS-SIM using an isotope dilution technique with [13C6] IAA as an internal standard. Throughout development, the majority of IAA was present in a conjugated form and the dominant form was amide IAA. The proportions of amide and free IAA changed rapidly after plants were water stressed until day 3, and preceded the doubling of fresh and dry weight. Correlation coefficients of 0.9, 0.7, and 0.7 (p<0.l) were found between auxin content and fresh weight, dry weight, and rate of water uptake, respectively.
Cynthia B. McKenney, Amber Bates, Kaylee Decker, and Ursula K. Schuch
Ursula K. Schuch, H. Brent Pemberton, and Jack J. Kelly
Five cultivars of bare-root rose plants were exposed to increasing periods of drying and after rehydration were grown in containers until flowering in a plastic-covered greenhouse. At the start of the experiment, moisture content of well-hydrated roses was between 51% and 56%. Five or 7 h of drying resulted in moisture contents below 43% for four of the cultivars and caused up to 80% mortality, increased time to flower, and decreased the number of flowering shoots. ‘First Prize’ was most tolerant of drying conditions and all plants survived, whereas ‘Mister Lincoln’ plants were most susceptible and had poor regrowth performance. Whole-plant moisture of ‘Mister Lincoln’ was similar to that in the stem or shank, which means that aboveground components instead of the entire plant can be used for moisture determination.
Ursula K. Schuch, Leslie H. Fuchigami, and Mike A. Nagao
Unsynchronized flowering and fruit ripening of coffee prohibits mechanical harvesting and results in high labor costs. Coffee (C.arabica c. Guatemalan) trees were sprayed at the beginning of the 1988 and 1989 flowering season with solutions of benzyladenine (BA), gibberellic acid GA3 (GA), and Promalin (PR) or were pruned in 1988 to determine effects on synchronizing flowering and ripening. Growth regulators affected the time to flowering and harvesting compared to the control, however, treatment effects were dependent on the time of growth regulator application. Application of PR and GA at 100 mg/l in Jan 1988 shortened the average days to flowering by 16 and 13 days, and the average days to harvest by 15 days compared to the control. Pruning of three apical nodes of primary lateral branches in Feb 1988 caused delays in flowering, reduced flower and fruit number per tree, and caused branch dieback.
Ursula K. Schuch, Richard A. Redak, and James A. Bethke
`Fontana', `Iridon', `Pink Lady', `Splendor', `White Diamond', and `White View Time' chrysanthemum (Dendranthema × grandiflorum Ramat.) were grown for 10 weeks with N rates of 80, 160, or 240 mg·L-1 constant liquid fertilization and irrigated at sufficient (high) or deficient (low) amount. Cultivars differed in growth habit, and treatments significantly affected all variables measured. Plants fertilized with 80 mg·L-1 had lower leaf and stem dry mass, less leaf area, and were deficient in leaf N compared with plants fertilized with twice the amount of N. The highest stem dry mass was produced with 160 mg·L-1. Leaf and stem dry mass were reduced 25% for plants receiving low irrigation compared to those receiving high irrigation. In general, leaf area increased when fertilizer was raised from 80 to 160 mg·L-1 but differed by cultivar and irrigation regime when fertilizer was increased to 240 mg·L-1. Three weeks after the experiment started, electrical conductivity (EC) of runoff collected weekly from `White Diamond' plants fertilized with 240 mg·L-1 exceeded the average EC of the irrigation solution. The 240 mg·L-1 treatment also resulted in excessive EC in the growing substrate at the end of the experiment and reduced stem dry mass by 11% compared with the 160 mg·L-1 fertilizer regime. Substrate EC differed between cultivars in response to fertilizer and irrigation. Significantly more adult western flower thrips [Frankliniella occidentalis (Pergrande)], 55% and 52%, were found on the foliage of `Pink Lady' and `Fontana', respectively, than on `Iridon'. `Pink Lady' and `Fontana' had more immature thrips at the end of the experiment than `Iridon' and `White View Time'. Fewer adults and immatures were found on plants fertilized with 80 mg·L-1 than 240 mg·L-1. Fewer adults were detected in plants under high versus low irrigation, while irrigation had no effect on the number of immatures. The simultaneous use of plant varietal resistance and plant cultural growing techniques has the potential to lower thrips populations on chrysanthemum.
Ursula K. Schuch, Leslie H. Fuchigami, and Mike A. Nagao
The effects of water stress and GA, on breaking dormancy of flower buds of coffee (Coffea arabica L.) were investigated. In the first experiment, water was withheld until the trees reached leaf water potentials (WP) of -1.20, - 1.75, -2.65, or -3.50 MPa. Water potential, ethylene production, and ion leakage of flower buds and leaf disks were examined from release from water stress until anthesis. Trees that had experienced leaf WP of less than - 2.65 MPa, and flower bud WP of about - 4.0 MPa flowered within 9 days after irrigation. In flower buds where dormancy had been broken with water stress, ethylene production was low compared to dormant buds and flowers at anthesis. In the second experiment, O, 50, 100, or 200 mg GA3/liter was painted on branches of nonstressed trees. In experiment three, water was withheld until plants reached leaf WP of -0.6, -1.3, - 2.1, or - 3.0 MPa, then two branches per tree were painted with O, 50, and 100 mg GA3/liter. Gibberellic acid partially compensated for insufficient water stress to initiate flower opening. Ethylene evolution of flower buds was affected by water stress but not by GA3 treatment. Severe water stress treatments and GA, treatment (200 mg·liter-1) increased ethylene evolution of leaf disks. Ion leakage of flower buds and leaf disks was increased by severe water stress. Ion leakage of flower buds was highest at anthesis. After water stress, dormant and nondormant flower buds at the 4-mm stage could be distinguished based on their ethylene evolution. Chemical name used: gibberellic acid (GA3).