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).
Martin Baz and R. Thomas Fernandez
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.
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.
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.
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.
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.
R. Thomas Fernandez, Ronald L. Perry, and James A. Flore
`Imperial Gala' apple trees (Malus ×domestica Borkh.) on M.9 EMLA, MM.111, and Mark rootstocks were subjected to two drought-stress and recovery periods in a rainshelter. Water relations, gas-exchange parameters per unit leaf area and per tree, chlorophyll fluorescence, and leaf abscisic acid content were determined during each stress and recovery period. Whole-plant calculated gas exchange best indicated plant response to drought stress, with consistent reductions in CO2 assimilation, transpiration, and leaf conductance. Variable and maximal chlorophyll fluorescence and fluorescence quenching were not as sensitive to stress. Other fluorescence parameters showed little difference. The most consistent decreases due to stress for gas exchange per square meter were in transpiration and leaf conductance, with few differences in CO2 assimilation and fewer for mesophyll conductance, internal CO2 concentration, and water-use efficiency. Leaf water potential was consistently lower during drought stress and returned to control values upon irrigation. Leaf abscisic acid content was higher for drought-stressed trees on M.9 EMLA than control trees during the stress periods but inconsistently different for the other rootstock treatments. Trees on M.9 EMLA were least affected by drought stress, MM.111 was intermediate, and Mark was the most sensitive; these results are consistent with the growth data.
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.
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.
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.