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James A. Robbins

Starting in 1999, the University of Arkansas implemented an annual workshop to prepare employees of the landscape and retail sectors for the spring rush. Since the sales and service sectors account for 91% of the annual gross sales for the Arkansas Green Industry it was felt a specialized workshop was justified. The program format consists of three, one-hour sections devoted to the most common disease, insect, and weed problems that these professionals face. The program is presented in the evening so more employees can attend. The format has changed over the years from the typical road-trip, to a compressed video conference format, and finally back to a live performance in the two major population markets in the state. A detailed handout is provided so participants can easily follow the program. These same notes serve as a handy reference when these employees return to their jobs. To further expand the audience, an interactive CD is now available that summarizes the three topic areas. Because the CD program is hyperlinked, viewers can either proceed through the program in a linear fashion or easily search for answers on specific topics of interest. For disease and insect topics, life cycle and host information is provided. Control measures are separated into chemical and biological options. A recent addition to the CD is the inclusion of actual photographs of consumer products to illustrate examples of suitable active ingredient options for the control of specific pests or diseases.

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James L. Green, James A. Robbins and Bruce A. Briggs

A closed, insulated, pallet production system (CIPPS) has been designed to meet current challenges: 1) Elimination of production related pollution. 2) Reduction and conservation of resources. 3) Improvement of working conditions. 4) Alternatives to pesticides. 5) Prevention of temperature extremes and rapid temperature fluctuations in the plant environment. Biological feasibility of CIPPS was established in research on pathogen epidemiology, water and fertilize efficiency, plant growth and development in CIPPS. Water and fertilizer ion movement-removal in the closed system was plant-driven in response to growth and transpiration; water and fertilizer use in CIPS was 10% of that applied to open containers. Growth of 28 plant species ranging from herbaceous annuals to woody perennials was greater in CIPPS than in control, individual containers. Phytophthora cinnamomi did not spread from inoculated to noninoculated plants within CIPPS. Inoculation with nonpathogenic bacteria increased plant growth (gfw) in CIPPS but not in open plant containers.

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Amy N. Wright, James A. Robbins and Mengmeng Gu

An online survey was conducted to gain information about nursery management and production (NMP) course content and enrollment, attitudes regarding the use of multimedia resources in the classroom, and opinions about the use of virtual field trips to supplement or replace traditional field trips. Results reflected current organizational and curriculum changes within colleges of agriculture that have impacted traditional horticulture courses such as NMP and in many cases have resulted in the merging of NMP courses with other courses such as greenhouse or garden center management. The number of departments with “horticulture” in the department name was similar to the number of departments with “plant science” in the department name (and not “horticulture”). The five topics covered most frequently included container production, container substrates, fertility, field production, and pot-in-pot production. Most of the respondents indicated that the NMP course in their department included at least one field trip. The top criteria used for selecting field trip locations included type of nursery, distance, innovation, reputation, and the number of aspects that could be viewed. Accessibility and distance to nurseries were listed as primary limitations for providing comprehensive field trips. Most respondents currently use multimedia resources in courses other than NMP, and a majority of respondents indicated that multimedia resources such as DVDs or web-based videos would be valuable for supplementing instruction in NMP, particularly for aspects not observed during field trips.

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Mengmeng Gu, James A. Robbins and Curt R. Rom

One-year-old paper birch (Betula papyrifera Marsh.) seedlings were exposed to water deficit, ethylene, or inhibitors of ethylene action under greenhouse conditions to investigate ethylene's role in water-deficit stress-induced leaf abscission. Exposing well-watered and water-stressed paper birch to 20 ppm ethylene resulted in more than 50% leaf abscission after 96 h regardless of plant water status. However, application of a physiological level (1 ppm) of ethylene did not cause leaf abscission in either well-watered or water-stressed paper birch. Inhibitors of ethylene action (1ppm 1-methylcyclopropene or 0.1 mm silver thiosulfate) did not affect predawn water potential, gas exchange, or chlorophyll fluorescence. A significant increase in ethylene production was not detected in water-stressed paper birch before the onset of significant leaf abscission. Based on these observations, ethylene would appear to play a minor role in water-deficit stress-induced leaf abscission in paper birch.

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Mengmeng Gu, Curt R. Rom and James A. Robbins

Four birch taxa, Betulaalleghaniensis, B. davurica, B. nigra `Heritage', and B. papyrifera, were grown in a greenhouse and exposed to water deficit stress for 35 days. Daily water was withheld from the plants until the combined weight of each container and the plant was reduced to 40% of the control. Supplemental water was supplied to each container to maintain 40% of the initial combined weight. Predawn water potential, gas exchange, and abscised leaf area were measured daily during the first week and at 3-day intervals after the first week. Predawn water potential dropped to lowest value before the containers were rehydrated and remained low throughout the treatment period. Net CO2 assimilation (A), stomatal conductance (gs) and evapotranspiration (Et) of all taxa decreased significantly during the first week of water deficits. Changes in A and Et varied among taxa after the first week of water deficits. Water use efficiency (WUE = A/Et) of four birch taxa decreased to significant lower values than control in the first week that water was withheld, and then increased to significantly higher values than control. Gas exchange data were fit into 2- or 3-segmented linear model. The type and shape of the models, and the joint of each segment gave an indication of how the gas exchange responded to the long-term water deficit stress. At the end of the water deficit treatment, B. papyrifera had abscised most of its leaves and maintained a high A, while B. alleghaniensis maintained more leaves on the tree, but had a relatively low A.

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Mengmeng Gu, James A. Robbins, Curt R. Rom and Jason McAfee

Japanese beetle (Popilla japonica Newman) has caused severe damage on a wide range of horticultural crops since its first introduction to the Eastern United States from Japan in 1916. Leaves are skeletonized by adult beetles feeding in masses, which makes this insect damage easy to identify. In Arkansas, Japanese beetle was first trapped in Washington County in 1997 and has reached epidemic proportions in the most recent three years. Leaf skelotonization and feeding preference on eighteen birch accessions by Japanese beetle were recorded in 2003 and 2004. There was a wide range from no feeding (0% leaf skelotonization) to high feeding preference (89% leaf skelotonization). Betula utilis var. jacquemontii and B. papyrifera `Renaissance Upright' had highest preference. Betula pendula `Laciniata' had no feeding damage from Japanese beetle.

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Kimberley Dennis, John R. Clark and James A. Robbins

Studies were conducted from January to November of 2005 to determine the effect of root-cutting length on adventitious shoot yield and the management practices necessary to produce nursery-quality blackberry plants. The first portion of the study measured the average number of shoots produced from 7.6 and 15.2 cm long root cuttings of APF-44 blackberry—a primocane-fruiting clone (not available in commerce) from the University of Arkansas breeding program. Cuttings were forced in a shallow bin containing soilless potting media. The average number of shoots per root cutting from 7.6- and 15.2-cm-long root cuttings averaged 1.6 and 2.7 shoots per root cutting, respectively. Rooting percentage of shoots was near 100% regardless of root cutting length and produced rooted plants of equal quality. The latter part of the study included various treatments on the rooted shoots that might affect the productivity and quality of the final product intended for nursery sales in early fall. With the aim of producing a flowering/fruiting shrub by late September, three treatments were applied: pot dimension, fertilizer rate, and shoot tipping. Fertilizer rate had the greatest impact of all treatments. Above normal summer/fall temperatures may explain lack of fruiting on APF-44 blackberries, but the dimension and size of some plants provided a portion of the intended aesthetic.

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Mengmeng Gu, James A. Robbins, Curt R. Rom and Hyun-Sug Choi

Net CO2 assimilation (A) of four birch genotypes (Betula nigra L. ‘Cully’, B. papyrifera Marsh., B. alleghaniensis Britton, and B. davurica Pall.) was studied under varied photosynthetic photon flux density (PPFD) and CO2 concentrations (CO2) as indicators to study their shade tolerance and potential for growth enhancement using CO2 enrichment. Effect of water-deficit stress on assimilation under varied PPFD and (CO2) was also investigated for B. papyrifera. The light saturation point at 350 ppm (CO2) for the four genotypes varied from 743 to 1576 μmol·m−2·s−1 photon, and the CO2 saturation point at 1300 μmol·m−2·s−1 photon varied from 767 to 1251 ppm. Light-saturated assimilation ranged from 10.4 μmol·m−2·s−1 in B. alleghaniensis to 13.1 μmol·m−2·s−1 in B. davurica. CO2-saturated A ranged from 18.8 μmol·m−2·s−1 in B. nigra ‘Cully’ to 33.3 μmol·m−2·s−1 in B. davurica. Water-deficit stress significantly reduced the light saturation point to 366 μmol photon m−2·s−1 but increased the CO2 saturation point in B. papyrifera. Carboxylation efficiency was reduced 46% and quantum efficiency was reduced 30% by water-deficit stress in B. papyrifera.

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Jon T. Lindstrom, James A. Robbins, Gerald L. Klingaman, Scott Starr and Janet Carson

The University of Arkansas established a new, replicated, woody ornamental plant evaluation program in 1999. Three sites were used across the state and these sites encompassed the three different USDA Plant Cold Hardiness Zones found in Arkansas, Zones 6, 7 and 8. In the first year, 17 different woody ornamental plants were established in the evaluation. Information obtained from performance in this evaluation will be used in Arkansas Select, a marketing program for customers and nurserymen in the state. Nonpatented and nontrademarked plant material will be made available for propagation purposes. Woody plants will be evaluated for 5 years and herbaceous perennials will be evaluated for 3 years.

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Mengmeng Gu, Curt R. Rom, James A. Robbins and Derrick M. Oosterhuis

Water was withheld from 2-year-old seedlings or rooted cuttings of four birch genotypes (Betula alleghaniensis Britton, B. davurica Pall., B. nigra L. ‘Cully’, and B. papyrifera Marsh.) until the combined weight of the container and plant decreased below 40% of its original value to induce plant predawn water potential between −1.5 MPa and −2.1 MPa, after which plants were supplied with a requisite amount of water to reach 40% of its original value for 5 weeks under controlled conditions to investigate changes in gas exchange, osmotic solutes, leaf abscission, and growth compared with well-watered (WW) plants. Observations indicated that three of the four genotypes (except B. papyrifera) expressed three stages of photosynthetic response during water deficit: 1) a stress stage, 2) an acclimation stage, and 3) an adapted (or tolerance) stage. The stages were characterized by decreasing, increasing, and stabilized Pnws/ww (net photosynthesis presented as a ratio of water-deficit stressed (WS) plants to WW plants), respectively. A strong relationship between Pn and g S observed in the WS plants of the four genotypes, suggested inhibition of Pn by stomatal closure. After exposure to water deficit for 5 weeks, Pnws/ww recovered to 70% of the initial value for B. alleghaniensis and B. nigra ‘Cully’ and 98% for B. davurica and B. papyrifera. WS plants had higher foliar concentrations of chlorophyll a and b (nmol/g) and potassium (%) than the WW plants. Increased levels of polyols (mg/g) were detected only in the WS plants of B. allegahaniensis. Increased levels of carbohydrates or organic acid under water deficit were not detected. A significant increase in leaf abscission in the WS plants of B. papyrifera compared with the other genotypes could be a morphological adaptation to water deficit conditions and facilitate recovery of Pnws/ww during the acclimation stage.