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Melissa B. Riley

Herbicide use in containerized plant production nurseries is a vital tool for weed management and the production of plants desired by the consumer. Clemson University researchers have conducted studies aimed at determining the amount of herbicide runoff during normal nursery operation, if herbicides accumulate in containment ponds at nurseries, and how herbicide runoff could be reduced. A 2-year study at commercial nurseries found that herbicide concentrations were higher in containment ponds soon after herbicide application, when compared with months with less herbicide application; and herbicides did not accumulate over the 2-year period. Herbicide runoff was greatest immediately after application and up to 15% of the herbicide applied was lost in the first irrigation event after application when using more water soluble herbicides. Bed material and herbicide formulation were also important in determining the amount of herbicide lost. Total losses were highest from plastic- and fabric-covered beds when using granular formulations and highest from gravel beds when spray formulations were used. The combination of using cyclic irrigation and grass waterways resulted in a reduction of about 25% of isoxaben loss when compared with clay and gravel waterways with continuous irrigation. The effects of reduced herbicide treatments compared to standard spray schedules were evaluated on herbicide transport, weed development, and plant growth and health. Results indicated that plant marketability was not affected, and total herbicide runoff was significantly reduced. Based on these studies, several recommendations can be made to commercial container plant production nurseries, which should reduce herbicide runoff and thereby reduce the environmental concerns associated with nurseries.

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Jeanne Briggs, Ted Whitwell, Melissa B. Riley and Tom Fernandez

This study investigated effects of two pesticide applications regimes, Integrated Pest Management (IPM), in which pesticides were only applied to affected plants when damage was noticed, and Traditional, in which pesticide applications were made on a scheduled and preventative basis, on growth and health of container grown plants. Field research was conducted at a large wholesale nursery in the piedmont region of South Carolina. An isolated portion of the nursery contained eight beds that housed 25 species of woody and herbaceous ornamentals. IPM beds were subjected to weekly in-depth scouting of indicator species, and all other plant materials in both treatments were visually checked for problems on a weekly basis. The study began in June 1998 with weekly scouting ending in late October. Monthly scouting continued through the winter of 1999. Runoff water was collected from the treatments after all pesticide applications and analyzed to determine concentrations of chemicals. Plant health was rated at study's end to allow comparison between treatments. Amounts of isoxaben detected in runoff water were 7.9 g for the traditional treatment and 0.9 g for the IPM treatment. Amounts of thiophanate-methyl and chlorothalinol were similarly lower for the IPM treatment. Preliminary results indicate that plant growth was similar for both treatments.

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Gretchen L. Mondt, Melissa B. Riley and Ted Whitwell

Recent research indicated that the herbicide simazine dissipated quickly in gravel-based subsurface-flow constructed wetlands. This indicates that retention areas at nurseries may be developed to facilitate pesticide remediation and reduce offsite movement. A site to simulate runoff retention areas at a containerized nursery was established with troughs containing pea gravel and controls containing no gravel in an open field. Irrigation water was applied daily to replace half of the capacity of the trough, simulating daily irrigation and runoff at a nursery. A study was conducted to determine the effects of this system on isoxaben (a pre-emergent herbicide) concentrations in the water leaving the troughs and the change in microbial organisms associated with the gravel. Initially, 19 L of a dilute isoxaben solution (1.3 μg/L) was added to each tank. Drainage was collected and assayed for isoxaben concentration over a 40-day period. Isoxaben was detected in troughs containing gravel through 14 days while isoxaben was detected in troughs containing no gravel through only 4 days. Microbial analysis of the gravel showed a variety of microorganisms initially, but, by day 14, Pseudomonas spp. became the dominant genus present. Preliminary analysis revealed that the isoxaben binds to the gravel, and is then desorbed over time. Further investigations will include the abilites of Pseudomonas and other isolated organisms to metabolize isoxaben as the sole carbon-source in the laboratory.

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Sorua L. Maki, Melissa B. Riley and Nihal C. Rajapakse

Endogenous gibberellins of chrysanthemum [Dendranthema ×grandiflorum (Ramat)] cv. Bright Golden Anne were characterized in apices from plants grown under control and CuSO4 spectral filters. Expanding shoots were separated into young expanding leaves and apices. Methanolic extracts of young expanding leaves were purified by solvent partitioning, PVPP column chromatography and reversed-phase high performance liquid chromatography. Two bioactive regions corresponding to the HPLC retention times of GA1 and GA19 standards were detected in fractions using the recently-developed non-dwarf rice bioassay. Di-deuterated internal standards of GA12, GA53, GA19, GA20, and GA1 were added to similar extracts of shoot apices. The presence of endogenous GA53, GA19, GA20, and GA1 in chrysanthemum apices was confirmed by isotope dilution using gas chromatography-mass spectrometry-selected ion monitoring and Kovats retention indices. In a preliminary quantification study, GA20 and GA1 levels were found to be higher in apices from plants grown under control filters while GA19 levels were higher in apices grown under CuSO4 filters. The possibility that light transmitted through CuSO4 filters alters gibberellin levels in shoot apices is discussed.

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Katherine A. Ellingson*, Nihal C. Rajapakse and Melissa B. Riley

Recent medical interest in plant antioxidants in human health has stimulated the interest in functional phytochemicals of fruits and vegetables. Numerous reports link antioxidant capacity of phytochemicals to the reduction of degenerative diseases. As a result, sales of herbal antioxidant supplements have increased tremendously although negative (or no) effects have been documented with certain supplements. There are many interactive reactions among phytochemicals. At this point, our understanding of interactions among phytochemicals is limited. Therefore, medical professionals are reluctant to prescribe supplements as a mean to boost antioxidants, but they agree that consumption of fresh fruits and vegetables is essential for a healthy life and provides a better alternative than supplements to boost antioxidant uptake. Carotenoids are receiving attention because of their pro-vitamin A activity and antioxidant properties. Two of the widely investigated carotenoids for improvement are lycopene and β-carotene. Genetic composition, cultural practices, environmental conditions, and processing can all affect carotenoid profiles. Light has been shown to affect carotenoids and we are investigating if changing the spectral composition in the growing environment can alter carotenoid levels. Preliminary results show that tomatoes grown under a high red light environment have increased lycopene and overall carotenoid contents. Nutritionally enhanced produce will benefit both growers and consumers.

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Jeanne Briggs, Ted Whitwell, R. Thomas Fernandez and Melissa B. Riley

Field research was conducted at a container nursery to investigate fungicide movement in runoff water. Fungicides were applied as either a preventative treatment to all container plants, or as a component of an integrated pest management (IPM) program in which fungicides were only applied to plants showing signs of pathogen infestation. Thiophanate-methyl and chlorothalonil were applied in July and August 1998, and metalaxyl was applied in September 1998. Runoff water was sampled on the day after application (first irrigation after pesticide application) through three pulse irrigation cycles. Total amounts of thiophanate-methyl and chlorothalonil in runoff water were 7% and 4%, respectively, of applied amount in July. In August, 2% and 4% of thiophanate-methyl and chlorothalonil were found from the preventative treatment. Of the applied metalaxyl, 25% was detected in runoff water for the first irrigation event after application from the preventative treatment. Metalaxyl is a highly water soluble pesticide and nontarget losses from the granular application contributed to the large amounts detected. Total amounts of thiophanate-methyl, chlorothalonil and metalaxyl detected in runoff from the IPM treatment were 25% of amounts from the preventative treatment. No treatment differences were found in container plant salability or in the number of culls at the end of the study.

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Matthew Cousins, Charles A. Gresham, Melissa B. Riley and Ted Whitwell

Beach Vitex (Vitex rotundifolia Lf.) was introduced to coastal Carolina areas in the 1980s. Since its introduction, it has become a major invasive plant problem. Beach Vitex rapidly dominates the vegetation and eliminates many native plant species on primary and secondary coastal dunes. It grows rapidly and reproduces vegetatively by rooting at the nodes. Thousands of fruits, containing one to four seeds each, are produced annually and assist in the plant's spread. Beach sand in areas dominated by Beach Vitex was found to possess hydrophobic qualities, while sand collected from areas not populated by Beach Vitex readily allowed water infiltration. GC-MS analysis of hydrophobic sand extracts showed four peaks that were absent from extracts of non-hydrophobic sand. These peaks were also present in chromatograms of water extracts of Beach Vitex fruits and leaves. Comparison of GC-MS spectra with compounds previously identified in Beach Vitex indicated that one compound was a diterpene (likely ferruginol or abietatrien-3ß-ol). The second compound is likely a flavonoid (possibly casticin, artemetin, or vitexicarpin). Two additional compounds are present at low levels and are possibly phenylnaphthalene compounds. These four compounds appear to be synthesized and incorporated into surface tissues of Beach Vitex leaves and fruits and are transferred to sand during rain events and decomposition. Further studies of Beach Vitex plant parts and beach sands are being conducted to further elucidate the possibility that these chemicals are involved in the intriguing property of sand hydrophobicity. This property may aide Beach Vitex in its competition with plants possessing less expansive root systems.

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R. Thomas Fernandez, Ted Whitwell, Melissa B. Riley and Cassandra R. Bernard

Canna ×generalis L.H. Bail. (canna), Pontaderia cordata L. (pickerel weed), and Iris L. × `Charjoys Jan' (`Charjoys Jan' iris) were exposed to a 5 mg·L-1 suspension of isoxaben or oryzalin or a water control for 9 days. Growth and photosynthetic responses were monitored throughout treatment and for an additional 22 d after termination of treatment. By the end of the experiment plant height of pickerel weed was reduced by oryzalin. Isoxaben resulted in lower height and reduced leaf emergence for all three taxa by the end of the experiment. Leaf CO2 assimilation (A) and transpiration (E) were lower for oryzalin-treated canna only 17 and 18 days after treatment, several days after treatment had been terminated. Leaf A and E were lower for oryzalin-treated pickerel weed and `Charjoys Jan' iris for most days after day 17. Isoxaben reduced A and E of all three plants for all days measured except day 6 for `Charjoys Jan' iris. Lower photosystem II efficiency (Fv/Fm) was found for isoxaben-treated canna from day 5 onward and days 7, 20, and 23 for pickerel weed and `Charjoys Jan' iris. Rapid reduction in A and Fv/Fm for all plants treated with isoxaben indicates a direct effect of isoxaben on photosynthesis. Reductions in growth and photosynthetic parameters due to oryzalin were minimal for all plants indicating these plants would be useful in phytoremediation systems where oryzalin is present. However, growth and photosynthetic parameters were reduced substantially for all plants exposed to isoxaben indicating the taxa studied would not perform well in phytoremediation systems with this level of isoxaben exposure. Chemical names used: isoxaben (N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyly]-2,6-dimethoxybenzamide); oryzalin (4-(dipropylamino)-3,5-dinitrobenzenesulforamide).

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Jorge M. Fonseca, James W. Rushing, Nihal C. Rajapakse, Ronald L. Thomas and Melissa B. Riley

The purpose of this review is to promote a discussion about the potential implications of herb production in controlled environments, focusing on our recent works conducted with feverfew. Research suggests that the content of secondary metabolites in medicinal plants fluctuates with changing environmental conditions. Our studies with feverfew (Tanacetum parthenium [L.] Schultz-Bip., Asteraceae) lend support to this hypothesis. Feverfew plants exposed to different water and light conditions immediately before harvest exhibited changes in content of some secondary metabolites. The highest yield of parthenolide (PRT) was in plants that received reduced-water regimes. Phenolics concentration however, was higher in plants receiving daily watering. Light immediately before harvest enhanced accumulation of PRT, but reduced the phenolic content. Notably, PRT decreased at night whereas total phenolics decreased during the photoperiod and increased at night. PRT also increased with increased plant spacing. UV light supplementation increased PRT only in plants that had undergone water stress, whereas phenolics increased when UV was applied to continuosly watered plants. Clearly, production of medicinal plants under greenhouse conditions is a promising method for controlling levels of phytochemicals through manipulation of light and water as discussed here, and possibly other environmental factors such as temperature and daylength. However, better understanding of how the environment alter secondary metabolite levels is needed as it was revealed that manipulating the environment to favor increased accumulation of one group of phytochemicals could result in a decline of other key metabolites.