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J.R. Evans, C.A. Ishida, C.L. Regusci, R.R. Evans, and W. Rademacher

Prohexadione calcium, or BAS-125W, is a plant growth regulator being developed for registration in the United States by the BASF Corporation and Kumiai Chemical Industry Co. Ltd. Prohexadione calcium inhibits the biosynthesis of gibberellin by blocking dioxygenases, which require 2-oxogluterate as a co-substrate. The result is a decrease in cell elongation and reduced vegetative growth. Gibberellin levels are reduced in the plant for 3 to 4 weeks following application of this growth regulator. Prohexadione calcium does not persist in the plant or directly effect vegetative growth the following season. Prohexadione calcium is absorbed by the plant foliage and uptake is generally complete within 8 hr following application. Results indicate that translocation within the plant is predominantly by acropetal movement, while basipetal movement is limited. Preliminary research has shown prohexadione calcium to have a short half-life in the environment; to have no negative effects on non-target organisms; and to offer little risk to users or consumers. Rates of 125 ppm a.i. to 250 ppm a.i. have typically provided effective vegetative control of vigorous apple trees. Generally, as the vegetative vigor of a tree increases; the rate of prohexadione calcium needed for effective vegetative control has to be raised. Vegetative vigor is influence by numerous factors including: fruit load, location, variety, rootstock, age, pruning, and training system. Earlier applications at 2 to 5 inches of new shoot growth have provided more-effective control of vegetative growth than later applications. Due to its short-term effect and lack of persistence, prohexadione calcium can be a flexible tool in developing user specific growth management strategies.

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J.R. Evans, R.R. Evans, C.L. Regusci, and W. Rademacher

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J.R. Davenport, C.A. Redulla, M.J. Hattendorf, R.G. Evans, and R.A. Boydston

An accurate yield map is imperative for successful precision farming. For 3 years (1998 to 2000) two to four potato (Solanum tuberosum) fields on a commercial farm in southeastern Washington were yield-monitored using commercial yield monitoring equipment without operator interaction. Multiple potato diggers were used to harvest the fields and diggers used were not necessarily the same at each harvest. In all years, yield monitoring data were missing due to equipment failure or lack of yield monitoring equipment on all diggers. Banding, due to dissimilar calibrations, different equipment used, or differential digger performance was observed in 1998 and 2000. Based on experience described here, some yield monitor data need minimal postprocessing or correction, other data need substantial postprocessing to make them usable, and other data may not be reliable due to equipment failure, improper calibration, or other causes. Even with preharvest calibration, it is still likely that the potato yield monitor data will need differential postprocessing, indicating that yield maps lack accuracy. In addition, comparison to yield data collected at multiple points within the field, this study found that the yield monitor over estimated potato yield. Thus, with some postprocessing, a useful yield map showing within field differences is possible. However, without significant postprocessing, the practice of using multiple diggers and yield monitors for potato harvest, both within and between fields, severely limits the ability to make consistent yield maps in commercial potato operations.

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Richard J. McAvoy, Bernard B. Bible, and Michael R. Evans

The early onset of bract necrosis in poinsettia (Euphorbia pulcherrima Willd. ex. Klotzch) is characterized by small dark-stained spots that precede the development of enlarged necrotic lesions. Electron micrographs of adaxial epidermal and subepidermal tissues with early symptoms of necrosis revealed large, electron-dense deposits in cell vacuoles. These spherical bodies resembled condensed tannins observed in the epidermal tissues of peach and apple fruit. Chemical analysis of bract tissues confirmed the presence of condensed tannins. Furthermore, there were higher concentrations of condensed tannin in bract samples with 2-mm-diameter lesions than in samples with lesions <0.5 mm (equivalent to catechin concentrations of 59 and 13 mg·g-1 fresh mass, respectively). No tannin bodies were observed in parallel samples of healthy-appearing bracts in which only trace concentrations of condensed tannins were measured (0.2 mg·g-1 fresh mass). The evidence suggests an association between condensed tannin accumulation in localized areas of the bract and the early appearance of bract necrosis symptoms.

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Michael R. Evans, Giampaolo Zanin, and Todd J. Cavins

Water-holding capacity represents the volume of water retained by a substrate after a saturating irrigation and drainage, and it is often referred to as container capacity. However, water-holding capacity is a time-specific measurement that is limited to the status of the substrate immediately after saturation and drainage. It does not provide information regarding how quickly water is lost from the substrate, the substrate water status over time, or the irrigation frequency required for a substrate under specific conditions. A new procedure was developed that generated a single numeric value that described the wetness of a substrate and in so doing took into account the substrate's water-holding capacity and drying rate. This value was referred to as an E-value. For substrates included in this study, E-values ranged from a low of 6 for parboiled fresh rice hulls (PBH) to a high of 93 for the commercial substrate Metro Mix 360. The procedure was shown to generate E-values that were as would be expected for the evaluated substrates and also ranked the substrates as would have been expected. Over repeated evaluations, the procedure was demonstrated to have a maximum inherent variability of plus or minus one E-value.

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Michael R. Evans, Todd J. Cavins, Jeff S. Kuehny, Richard L. Harkess, and Greer R. Lane

Economics and logistics have greatly reduced or eliminated the ability of horticulture instructors to use field trips or on-site visits as educational tools. This is especially problematic in the field of greenhouse management and controlled environment agriculture, since the facilities and technologies used are essential to the discipline. To address this problem, we developed 15 DVD-based virtual field trips (VFT's) that instructors may use to demonstrate to students the most up-to-date facilities, technologies, and management strategies used in greenhouse management (ornamental and food crops) and controlled environment agriculture (GCEA). Each VFT included a preface with background information about the company, a tour organized by subject chapters, self-examination, and a teacher's guide with additional information and case studies. Each land-grant institution with an instructional program in greenhouse management of controlled-environment agriculture will be provided a free copy of each VFT, which will benefit all instructors of GCEA in the United States.

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W. Rademacher, J.B. Speakman, G. Krack, M. Scholtissek, R. Wolf, J.R. Evans, S. Roemmelt, and D. Treutter

Prohexadione-Ca (BAS 125 W) is currently developed as an inhibitor of excessive vegetative growth in apple. In addition to the control of shoot growth, pronounced effects on the incidence of scab (Venturia inaequalis) and fire blight (Erwinia amylovora) are observed that are not due to any fungicidal or bactericidal effect of the compound. Prohexadione-Ca induces marked changes in the metabolism of phenylpropanoids most likely by inhibiting distinct dioxygenases, such as flavanone 3-hydroxylase, which require 2-oxoglutarate as a co-substrate. The content of flavonoids such as luteoliflavan (which does not normally occur in apple tissue) and eriodyctiol is drastically increased reaching levels in the range of 50 mg per gram of dried young shoot tissue. Simple phenols, the identity of which is still unknown, also undergo intense changes. Since phenylpropanoids have often been found to be involved in defense mechanisms of higher plants, further studies on their role in pathogen resistance in apple are justified from these results.

Open access

Nathan J. Eylands, Michael R. Evans, and Angela M. Shaw

Various saponins have demonstrated allelochemical effects such as bactericidal impacts as well as antimycotic activity against some plant pathogenic fungi, thereby acting to benefit plant growth and development. A commercial saponin solution was evaluated for bactericidal effects against Escherichia coli and growth of lettuce (Lactuca sativa) in a hydroponic system. E. coli (P4, P13, and P68) inoculum at final concentration of 108 colony-forming units (cfu)/mL was added to 130 L of a fertilized solution recirculating in a nutrient film technique (NFT) system used to grow ‘Rex’ lettuce. After 5 weeks in the NFT system, E. coli populations were lowest in the inoculated treatment that did not contain any saponin addition (0.89 log cfu/mL) when compared with all other inoculated treatments (P < 0.001). The treatment containing 100 µg·mL−1 saponin extract had an E. coli population of 4.61 log cfu/mL after 5 weeks that was higher than treatments containing 25 µg·mL−1 or less (P < 0.0001). Thus, higher E. coli populations were observed at higher saponin concentrations. Plant growth was also inhibited by increasing saponin concentrations. Fresh and dry shoot weight were both higher in the inoculated and uninoculated treatments without the saponin addition after 5 weeks in the NFT system (P < 0.0001). Lettuce head diameter was smaller when exposed to saponin treatments with concentrations of 50 and 100 µg·mL−1 (P < 0.0001). Lettuce leaves were also tested for the potential of E. coli to travel systemically to the edible portions of the plant. No E. coli was found to travel in this manner. It was concluded that steroidal saponins extracted from mojave yucca (Yucca schidigera) are not an acceptable compound for use in mitigation of E. coli in hydroponic fertilizer solution due to its ineffectiveness as a bactericide and its negative impact on lettuce growth.

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Michael R. Evans, Andrew K. Koeser, Guihong Bi, Susmitha Nambuthiri, Robert Geneve, Sarah Taylor Lovell, and J. Ryan Stewart

Nine commercially available biocontainers and a plastic control were evaluated at Fayetteville, AR, and Crystal Springs, MS, to determine the irrigation interval and total water required to grow a crop of ‘Cooler Grape’ vinca (Catharanthus roseus) with or without the use of plastic shuttle trays. Additionally, the rate at which water passed through the container wall of each container was assessed with or without the use of a shuttle tray. Slotted rice hull, coconut fiber, peat, wood fiber, dairy manure, and straw containers were constructed with water-permeable materials or had openings in the container sidewall. Such properties increased the rate of water loss compared with more impermeable bioplastic, solid rice hull, and plastic containers. This higher rate of water loss resulted in most of the biocontainers having a shorter irrigation interval and a higher water requirement than traditional plastic containers. Placing permeable biocontainers in plastic shuttle trays reduced water loss through the container walls. However, irrigation demand for these containers was still generally higher than that of the plastic control containers.

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J.R. Evans, J.A. Balles, B.A. Brinkman, V.E. Harris, J.D. Helm, K.B. Kirksey, T.E. McKemie, G.G. Thomas, and W. Rademacher

Prohexadione-Ca (BAS 12511W or Apogee™ Plant Growth Regulator) acts within a plant by blocking the biosynthesis of growth-active gibberellin. The result is decreased cell and shoot elongation; thus, vegetative growth in apple trees can be reduced. Air blast applications of prohexadione calcium were made in the Spring 1998 in commercial orchards. Application rate was 125 ppm a.i. applied twice beginning at 5 to 12 cm of new shoot growth. Reduction of shoot growth averaged 45% across locations. As a result of reduced vegetative growth, dormant pruning was reduced. In total, significant benefits to the grower included reduced pruning costs in addition to other positive effects such as improved light penetration and enhanced resistance to some pathogens. Research will continue with the effect of prohexadione-Ca on pruning in multiple year studies.