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Irrigation scheduling can be improved by directly monitoring plant water status rather than depending solely on soil water content measurements or modeled evapotranspiration estimates. Plants receiving sufficient water through their roots have cooler leaves than those that are water stressed, leading to the development of the crop water stress index, which uses hand-held infrared thermometers as tools for scheduling irrigations. However, substantial error can occur in partial canopies when a downward-pointing infrared thermometer measures leaf temperature and the temperature of exposed, hot soil. To overcome this weakness, red and near-infrared images were combined mathematically as a vegetation index, which was used to provide a crop-specific measure of vegetative cover. Coupling the vegetation index with the paired radiant surface temperature from a thermal image, a trapezoidal two-dimensional index was empirically derived capable of detecting water stress even with a low percentage of canopy cover. Images acquired with airborne sensors over subsurface drip-irrigated muskmelon (Cucumis melo L.) fields demonstrated the method's ability to detect areas with clogged emitters, insufficient irrigation rate, and system water leaks. Although the procedure needs to be automated for faster image processing, the approach is an advance in irrigation scheduling and water stress detection technology.
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).
Abstract
Muskmelon fruits were either dipped in or injected with 2-(4-chlorophenylthio-) triethylamine hydrochloride (CPTA) at half- and full-slip maturities prior to storage at various temperatures. Concentrations of 500, 1000, and 5000 ppm caused fruits to have more pink color and a higher ratio of red to yellow color than did those untreated. The greatest response to CPTA was in half-slip fruits. We believe that the pink color is associated with lycopene accumulation.
Water application efficiency can be improved by directly monitoring plant water status rather than depending on soil moisture measurements or modeled ET estimates. Plants receiving sufficient water through their roots have cooler leaves than those that are water-stressed, leading to the development of the Crop Water Stress Index based on hand-held infrared thermometry. Substantial error can occur in partial canopies, however, as exposed hot soil contributes to deceptively warm temperature readings. Mathematically comparing red and near-infrared reflectances provides a measure of vegetative cover, and this information was combined with thermal radiance to give a two-dimensional index capable of detecting water stress even with a low percentage of canopy cover. Thermal, red, and near-infrared images acquired over subsurface drip-irrigated cantaloupe fields demonstrated the method's ability to detect areas with clogged emitters, insufficient irrigation rate, and system water leaks.
Abstract
Production of commercial lettuce Lactuca sativa L. is plagued by a wide range of diseases and insects not yet controlled or only imperfectly controlled. These include the viral, virus-like, and mycoplasma diseases such as lettuce mosaic, cucumber mosaic, broad bean wilt, western yellows, big vein, and aster yellows; the fungal diseases—downy mildew and sclerotinia drop; and such insect pests as cabbage looper, beet army worm, white flies, and several species of aphids.
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.
The neotropical shrub Hamelia patens Jacq. has been cultivated as an ornamental in the United States, Great Britain, and South Africa for many years, although only in limited numbers and as a minor element in the trade. Recently, other taxa of Hamelia have been grown and evaluated as new flowering shrubs. The relatively recent introduction of a superior ornamental taxon of Hamelia, called the african firebush, has propelled this genus to greater prominence as an excellent small flowering shrub or container plant, especially throughout the southeastern United States and in other countries such as South Africa. Initially, this firebush was sold as an African plant. Data from field studies, herbarium specimens, and from DNA analysis of several taxa and populations of Hamelia show that the african firebush in southern Florida may have originated from populations of H. patens var. glabra native to southern Mexico. The original plants were taken to Europe, southern Africa, and southeastern Asia probably in the middle to late 1800s and then recently reintroduced to New World markets as a new African ornamental plant.
The neotropical shrub Hamelia patens Jacq. has been cultivated as an ornamental in the United States, Great Britain, and South Africa for many years, although only in limited numbers and as a minor element in the trade. In recent years, other taxa of Hamelia have been grown and evaluated as new flowering shrubs. The relatively recent introduction of a superior ornamental species of Hamelia called the “African firebush” has propelled this genus to greater prominence as an excellent small flowering shrub or container plant, especially throughout the southeastern United States and in other countries such as South Africa. Initially, this firebush was sold as an African plant. Data from field studies, herbarium specimens, and from DNA analysis of several taxa and populations of Hamelia show that the African firebush in southern Florida may have originated from populations of Hamelia patens var. glabra native to southern Mexico. The original plants were taken to Europe, southern Africa, and southeastern Asia probably in the mid to late 1800s and then recently re-introduced to New World markets as a new African ornamental plant.
Strawberry (Fragaria ×ananassa Duch.) genotypes retained for resistance to Verticillium wilt (Verticillium dahliae Kleb.) after two cycles of a two-stage (TS) selection procedure consisting of full-sib family selection followed by within-family selection of individuals, and genotypes retained for resistance using genotypic mass (GM) selection were crossed to a common set of moderately susceptible genotypes. The relative resistance of the seedlings from these progenies was compared using a resistance score and the percentage of stunted plants. Although the two sets of resistant parents had performed similarly in genotypic comparisons, those genotypes selected using the TS procedure yielded test cross offspring with significantly higher resistance scores (X̄ = 3.84 ± 0.09 vs. X̄ = 3.46 ± 0.09, t = 3.11**) and significantly lower rates of plant stunting (X̄ = 38.1% ± 3.1 vs. X̄ = 50.2% ± 2.9, t = 2.87**) than the parents chosen using GM selection. Further resolution using analysis of variance and general combining ability (GCA) estimates showed that these between-set differences resulted from higher resistance breeding values for parents selected using the TS procedure. The five genotypes with largest GCA for resistance score and four of the five genotypes with minimum GCA for percentage stunting were obtained by TS selection.
Sprays of calcium materials were applied at high volume rates (620 g Ca/400 liters) with a handgun during early June, late June, and mid-July versus mid-July, early August, and late August for five years, 1985 to 1989. Leaf injury was most severe for the late sprays but no spray injury was observed on the fruit surfaces. Bitter pit was markedly reduced with all sprays except CaSO4. In some years, bitter pit was controlled better with the early sprays. Either early or late sprays improved fruit quality including overall appearance, reduced scald development, improved red color of the skin, increased fruit firmness and reduced incidence of bitter pit in cold air (0°C) storage. Soluble solids and acidity in the fruit was not affected by calcium sprays. Leaf Ca was higher from the late spray applications than from the earlier applications. All calcium chloride spray materials resulted in increased fruit peel and cortex Ca. Calcium nitrate sprays tended to increase fruit nitrogen concentrations leading to undesirable higher N:Ca ratios in the fruit.