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Martin Baz and R. Thomas Fernandez

Itea virginica L. `Sprich' (virginia sweetspire), Salix alba L. (white willow), and S. gracilistyla var. melanostachys (Mak.) Miq. (black pussywillow) were treated with a 4 mg·L-1 suspension of two herbicides, isoxaben and oryzalin, a water control (water) or a nonsaturated control (control) for 9 days. Growth and photosynthetic responses were monitored before, during and after the 9-day treatment for a total of 51 days. Growth index of white willow and virginia sweetspire was only reduced by isoxaben treatment while both herbicides reduced the growth index for black pussywillow compared to control. Plant dry weights of the willows were not affected by day 9. Final dry weight was lower for both herbicide treatments for all taxa. The water treatment resulted in lower total dry weight than control only for virginia sweetspire. Isoxaben reduced photosystem II efficiency (Fv/Fm) and CO2 assimilation (A) following release from treatments of virginia sweetspire and black pussywillow. There were few differences in Fv/Fm and A for white willow. The response to oryzalin was similar to water for most parameters measured for virginia sweetspire and white willow. Growth was more strongly affected by oryzalin for black pussywillow than for other taxa but there were few differences in Fv/Fm or A between oryzalin and control for any of the taxa. Virginia sweetspire and white willow showed promise for use in phytoremediation of oryzalin but none of the taxa performed well under the levels of isoxaben used. 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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Dewayne L. Ingram and R. Thomas Fernandez

System-level research has resulted in significant advancements in horticultural crop production. Contributions of individual components to production efficiency, cost, and environmental impact have been a focus of such research. Public awareness of the environmental impact of products and services is increasing. Life cycle assessment (LCA) is a tool to study horticultural crop production systems and horticultural services and their individual components on environmental impacts such as the carbon footprint, stated as global warming potential. This manuscript introduces LCA and describes how this tool can be used to generate information important to the industry and consuming public.

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R. Thomas Fernandez and James A. Flore

Fruit of sweet cherry (Prunus avium L.) crack during or after rain due, in part, to absorption of water through the fruit surface driven by the water potential gradient. In 1972, J. Vittrup-Christensen suggested that overhead misting of calcium salts during precipitation may be an effective way to prevent cherry cracking by reducing the water potential gradient. We tested this hypothesis by designing a computer-controlled irrigation system to intermittently spray a 10% CaCl2 solution on trees during rain events. Spray emitters were placed in the middle and at the top of the canopy. The program turned the system on for 90 s at each 0.3 mm of rain and monitored daily rainfall and accumulated mist times. Two `Emperor Francis' and two `Ulster' were treated with equal number of controls. Intact and cracked cherries were counted on four branches per tree at three times when cherries were susceptible to cracking. Overall, cracking was reduced from 33% to 11% by the CaCl2 spray at the end of the experiment. Treated `Ulster' had 9% cracked fruit, while control had 43% cracked fruit. Differences for `Emperor Francis' were not significant. Phytotoxicity was estimated at about 15 % of leaf area. This system will be reevaluated in 1995 with the added objective of quantifying and reducing phytotoxicity.

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Damon E. Abdi and R. Thomas Fernandez

Ornamental nurseries produce a large number of plants in a concentrated area, and aesthetics are a key component of the product. To produce crops in this manner, high inputs of water, nutrients, and pesticides are typically used. Container nursery production further increases the inputs, especially water, because container substrates are designed to quickly drain, and the most effective method of irrigating large numbers of plants in containers (up to a certain size) is the use of overhead irrigation. Because irrigation and pesticides are broadcast over the crop, and because the crop is limited to the container, a large proportion of water or pesticides may land on nontarget areas, creating runoff contaminant issues. Water is the primary means of pesticide movement in nursery production. This review discusses water and pesticide dynamics and management strategies to conserve water and reduce pesticide and water movement during container nursery production.

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Amanda J. Taylor, R. Thomas Fernandez, Pascal Nzokou and Bert Cregg

The objective of this study was to quantify the effects of cyclic irrigation on growth and physiology of container-grown conifer species in pot-in-pot (PIP) production in the upper Midwest. Trees of four conifer species (Picea glauca var. densata, Picea pungens, Abies fraseri, and Pinus strobus) were grown in 25-L containers and assigned to one of four combinations of irrigation rate (low or high) and daily irrigation cycle frequency (one or four). Irrigation rates were based on common nursery practice in the region (2 cm rainfall equivalent/day) and one-half the standard rate (1 cm rainfall equivalent/day). Cyclic irrigation increased relative height growth and relative caliper growth of Pinus strobus by over 80% and 35%, respectively, compared with once-daily irrigation. The high-rate irrigation increased relative caliper growth of Picea pungens by 40% compared with the low rate. The effects of irrigation regime on needle- or shoot-level gas exchange varied by species and date of measurement. Carbon isotope discrimination (Δ13C) of needle and wood tissue was positively correlated (r ≥ 0.64, P < 0.001) with needle conductance to water vapor (gwv) and negatively correlated (r ≤ −0.60, P< 0.001) with intrinsic water use efficiency (WUEi). Carbon isotope discrimination of wood and needle tissue decreased with the low irrigation rate, indicating increased WUEi associated with reduced gwv. Cyclic irrigation had relatively little effect on Δ13C except for Pinus strobus. Our findings suggest that carbon isotope composition of wood and needle tissue provides a sensitive and accurate representation of plant response to varying moisture availability. From a water management perspective, identifying optimal irrigation rates appears to be more important than number of daily cycles for these crops grown in the midwestern United States.

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Kelly J. Prevete, R. Thomas Fernandez and William B. Miller

Boltonia asteroides L. `Snowbank' (Snowbank boltonia), Eupatorium rugosum L. (eastern white snakeroot), and Rudbeckia triloba L. (three-lobed coneflower) were subjected to drought for 2, 4, and 6 days during the fall and spring. Leaf gas exchange, leaf water potential, growth, and carbohydrate partitioning were measured during drought and throughout the following growing season. Leaf gas exchange of B. asteroides was not affected by drought treatment in the fall, not until day 6 of spring drought, and there were no long-term effects on growth. Transpiration and stomatal conductance of R. triloba decreased when substrate moisture decreased to 21% after drought treatment during both seasons. Assimilation of drought-treated R. triloba decreased when substrate moisture content decreased to 12% during spring but was not affected by drought in the fall. There was a decrease in the root-to-shoot ratio of R. triloba that had been treated for 4 days, which was attributed to an increase in the shoot dry weight (DW) of treated plants. Reductions in spring growth of E. rugosum were observed only after fall drought of 6 days, and there were no differences in final DWs of plants subjected to any of the drought durations. Spring drought had no effect on growth index or DW of any of the perennials. Boltonia asteroides and R. triloba had increases in low-molecular-weight sugars on day 4 of drought, but E. rugosum did not have an increase in sugars of low molecular weight until day 6 of drought. Differences in drought response of B. asteroides, E. rugosum, and R. triloba were attributed to differences in water use rates.

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Kelly J. Prevete, R. Thomas Fernandez and William B. Miller

Drought stress durations of 2, 4, and 6 days were imposed on Boltonia asteroides `Snowbank', Eupatorium rugosum, and Rudbeckia triloba to determine the effects on carbohydrate partitioning in the plant. Drought stress was imposed on 19 Sept. 1997 on 1.9-L containerized plants. Plants were planted in the field the day following release from stress. Crown and leaf samples of the three species were collected 21, 23, 25 Sept. 1997 and 30 Jan. and 4 May 1998 and were analyzed for low molecular weight sugars and fructans. The species differed in the time it took for longer chain fructans to break down to shorter chain fructans and low molecular weight sugars (glucose, fructose). The drought tolerant Boltonia and Rudbeckia had shifts from longer chain to shorter chain fructans by day 4 of stress. Boltonia had a change in carbohydrate partitioning in the leaf tissue, while Rudbeckia had a change in crown tissue carbohydrate partitioning. Eupatorium did not have a shift in longer chain fructans to shorter chain fructans in crown tissue until day six of stress. The slower shift from longer chain fructans to shorter chain fructans by Eupatorium, compared to Boltonia and Rudbeckia, could explain the lack of drought tolerance of Eupatorium. The shift from high molecular weight sugars to low molecular weight sugars suggests that the higher molecular weight sugars broke down to lower molecular weight sugars in response to drought stress.

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R. Thomas Fernandez, Robert E. Schutzki and Kelly J. Prevete

Responses of Magnolia ×soulangiana (Soul.-Bod.) `Jane' (`Jane' saucer magnolia) to consecutive short term pretransplant drought stresses and recovery after transplanting were evaluated beginning October 1997 and June 1998. Plants were subjected to one (mild) or two (moderate) 3-day drought stress periods or a two 3-day and one 4-day (severe) drought stress period, each separated by two rewatering periods over 24 hours. One day after each stress period, plants were transplanted into the field and well watered to monitor recovery from stress. Plant response was determined by measuring whole-plant CO2 assimilation, leaf gas exchange (CO2 assimilation, transpiration, stomatal conductance) and canopy growth throughout stress and recovery periods. Whole-plant and leaf CO2 assimilation were lower for the stressed treatments for most of the measurements taken during stress in the fall and spring. After release from stress and transplanting, leaf CO2 assimilation returned to control levels for mild and moderate fall stresses within 2 to 3 d by the next measurement, while it was over 3 weeks until recovery from the severe stress. There was no difference in leaf gas exchange following release from stress and transplanting during the spring stress. More rapid defoliation occurred for the severe fall-stressed plants compared to the controls after release from stress in the fall. Flower number was reduced in spring for the fall-stressed plants. At termination of the experiment, the growth index was lower for severe fall-stressed plants but there were no differences for other fall stress treatments. There was no increase in growth for control or stressed plants for the spring experiment.

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R. Thomas Fernandez, Ronald L. Perry and David C. Ferree

Root distribution of `Starkspur Supreme Delicious' on nine apple (Malus domestics Borkh.) rootstock grown in two different soil types in the 1980 NC-140 Uniform Apple Regional Rootstock Trial (Michigan and Ohio sites) was determined using the trench profile method. Based on the number of roots counted per tree, rootstock could be separated into five groups for the Marlette soil from most to least: MAC.24 > OAR1 > M.26EMLA = M.9EMLA > M.7EMLA = 0.3 = M.9 = MAC.9 > M.27EMLA. For the Canfield soil, rootstock were ranked for number of roots counted from most to least as follows: MAC.24 > OAR 1. MAC.9 = M.7EMLA > M.26EMLA = O.3 = M.9 EMLA = M.9. Root distribution pattern by depth was affected by soil type with roots fairly well distributed throughout the Marlette soil but restricted primarily above the fragipan in the Canfield soil. Two rootstock performed differently from others in adapting to soil conditions at the different sites. MAC.9 had the second lowest number of total roots/dm2 in the Marlette soil yet the second most in the Canfield soil, while the opposite was found for M.9EMLA. Regression analysis demonstrated positive correlations between number of roots counted and vigor and yield of the scion.

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R. Thomas Fernandez, Ronald L. Perry and James A. Flore

`Imperial Gala' apple (Malus domestica Borkh.) trees, trained to two shoots, on M.9 EMLA, MM.111, and Mark rootstocks were subjected to two drought-stress and recovery periods in a rainshelter. Leaf growth rate, leaf area, leaf emergence, shoot length, and trunk cross-sectional area were measured during each stress and recovery period. Leaf growth rate was reduced during both stress periods but most consistently during the second drought stress. Length of the less-vigorous shoot was reduced most consistently due to drought stress but did not recover upon irrigation. Leaf emergence and trunk cross-sectional area increment were inconsistent in response to stress. Tree growth was reduced by drought stress to the greatest extent for trees on Mark, with MM.111 intermediate and M.9 EMLA least affected. At termination, the plants were separated into roots, current-season shoot growth, previous-season shoot growth, and rootstock, and dry weights were measured. Dry weights confirmed the growth measurements taken during the experiment with a 16%, 27%, and 34% reduction in total plant dry weight for drought-stressed trees on M.9 EMLA, MM.111, and Mark, respectively, compared to corresponding controls. It was concluded that Mark was the most sensitive of the three rootstocks followed by MM.111; M.9 EMLA was the most drought resistant.