Greenhouse studies were conducted to evaluate simulated drift injury to annual bedding plants. Dahlia, gazania, geranium, marigold, petunia, and salvia in the early stages of flowering were sprayed with either 2,4-D (dimethylamine salt) or dicamba (diglycolamine salt) at rates one-fifth, one-tenth, or one-twentieth the lowest labeled rate of for turfgrass. Interactions between species by time, species by treatments, and treatments by time were significant for visual injury. Species sensitivity from most sensitive to least sensitive was marigold > dahlia ≫ geranium = petunia > gazania = salvia. Dahlia was more sensitive to dicamba than 2,4-D while the opposite was true for marigold. Petunia flower initiation was reduced as dicamba or 2,4-D rate was increased. The duration of the trial may have limited flowering differences among treatments with the remaining species. Dahlia loss of apical dominance as an injury response was greater with dicamba than 2,4-D. Typical injury symptoms for dahlia included stem, leaf, and petiole epinasty along with multiple shoot growth. Gazania injury included slight leaf rolling and leaf stretching. Geranium injury included leaf curling and fewer flowers per cluster. Marigold injury included leaf node swelling and stem wall rupture with massive cellular proliferation. Petunia injury included stem and pedicel epinasty, curling of the outer portion of the corolla, and lower flower production. Salvia injury included stunting, slight flower stem curvature, and partial dieback of the terminal raceme.
Steven F. Berkheimer and Eric Hanson
Injury has been observed since the early to mid-1990s to highbush blueberries (Vaccinium corymbosum L.) growing along roads in southern Michigan. Symptoms include shoot dieback, flower bud mortality, and reduced yields. To determine if this injury was the result of deicing salts applied to roads, salt (sodium chloride, NaCl) spray was applied to potted blueberry plants, and to the plant root zones. Bushes sprayed six times during the winter with NaCl solutions (0, 0.034, 0.068, 0.137, 0.274, 0.548 m) developed the same injury symptoms observed in roadside fields, and injury severity was proportional to the spray concentration. The root media of other potted plants was saturated with NaCl solutions (0, 0.017, 0.051, 0.154, and 0.462 m) in Mar. 2002. Pots were then rinsed with fresh well water when growth began in April to determine if soil salt caused similar damage. The highest soil salt levels killed most above ground growth, and damage diminished with decreasing salt levels. Twigs were also excised from branches sprayed twice with NaCl solutions or water and frozen incrementally to measure the temperature resulting in 50% flower bud mortality (LT50). Salt exposure reduced the LT50 of flower buds, by as much as 11.5 °C, relative to the control, even within 2 days of treatment. Additional studies with chloride salts (NaCl, KCl, CaCl2, MgCl2) and sodium salts (NaCl, Na-acetate, Na2SO4) indicated that most reduced the cold tolerance of blueberry flower buds to some degree.
Steven F. Berkheimer, Eric J. Hanson, Jason K. Potter, and Jeffrey A. Andresen
Some highbush blueberry (Vaccinium corymbosum) fields adjacent to Michigan roads exhibit abnormally high levels of winter fl ower bud mortality and twig dieback, even following relatively mild winters. This work was conducted to determine if this injury was caused by deicing salts (primarily sodium chloride) that are applied to adjacent roads and blown by the wind onto bushes. Flower bud mortality was recorded in the spring at several locations within six farms adjacent to divided highways treated with deicing salts. Four farms were east of highways (downwind of prevailing wind direction) and two were west (upwind) of highways. Each May for 3 years, the numbers of live and dead fl ower buds were counted on plants located varying distances from the highway. Bush position and distance from the highway were determined with global positioning system (GPS) equipment. Bud health was also assessed monthly during the winter. In fields located downwind of highways, bud mortality was consistently greatest close to the road and decreased with distance. Salt had an apparent effect on mortality 60 to 120 m from the highway, depending on the year. In fields west or upwind of highways, bud mortality was not consistently related to distance from the highway. Flower bud injury was evident by mid-January, and increased throughout the winter. Results indicated that wind-blown salt spray can cause considerable injury in blueberry fields close to salted roads.
Billy J. Johnson, Robert N. Carrow, and Tim R. Murphy
Field experiments were conducted to determine the effects of foliar iron (Fe) applied with postemergence herbicides on injury, color, and quality of `Tifway' bermudagrass [Cynodon transvaalensis Burtt-Davy × Cynodon dactylon (L.) Pers.]. Iron significantly decreased injury and improved quality and color of `Tifway' bermudagrass in conjunction with herbicide treatment. Turf injury was less for 4 to 18 days after the initial MSMA application when Fe was added. Injury was also less from sequential Fe treatment with MSMA + metribuzin (up to 4 days) and MSMA + imazaquin (from 4 to 10 days) compared to the respective herbicides applied alone. There was no difference in turf injury from Fe when imazaquin at 1.3 kg·ha-1 was applied as a single treatment. However, turf treated with Fe and two applications of imazaquin (9- to 10-day interval) recovered from herbicide injury faster than when treated only with the herbicide. Iron did not prevent immediate 2,4-D + mecoprop + dicamba injury to the bermudagrass, but did hasten turf recovery from injury at 26 days after treatment. With a few exceptions, `Tifway' bermudagrass quality was higher and color improved when Fe was added. However, injury expressed as loss of shoot density was not affected by Fe and only injury expressed as color loss was improved by Fe. Chemical names used: 3,6-dichloro-2-methoxybenzoic acid (dicamba), 2-[4,5-dihydro-4-methyl)-4-(1-methylethyl)-5-oxo-1H-imidazol-2yl]-3-quinolinecarboxylic acid (imazaquin), (±)-2-(4-chloro-2-methylphenoxy)propanoic acid (mecoprop), 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one (metribuzin), monosodium salt of MAA (MSMA), and (2,4-dichlorophenoxy)acetic acid (2,4-D).
Raul I. Cabrera and Pedro Perdomo
The performance of modern greenhouse-grown roses under intensive nutrient and water management practices questions their traditional classification as a salt-sensitive species, and emphasizes the need to reassess their salinity tolerance. Container-grown `Bridal Pink' roses (on R. manetti rootstock) in a peat moss-based growing medium were irrigated, using moderate leaching fractions (25% targeted, 37.5% actual), with complete nutrient solutions supplemented with NaCl at 0, 5, and 10 mm. These salt concentrations affected the electrical conductivity (EC) and Cl concentrations measured in the leachates, but had no significant effects on flower yield and quality over four growth and flowering flushes (§29 weeks). Cumulative yields over this period increased an average of §13% per leachate EC unit. Thereafter, the applied NaCl concentrations were increased 3-fold to 0, 15, and 30 mm and the plants continued to be evaluated for another four flowering flushes. No significant differences in cut-flower yield and quality were observed among salt treatments despite further increases in leachate EC and Na and Cl concentrations. Symptoms of salt injury were visually observed during the last three flowering cycles, and most heavily on the oldest foliage of plants receiving the highest salt concentration (30 mm), but not on the foliage of harvested shoots. The concentration of most nutrients in leaf tissue was not significantly affected by any of the treatments over the course of the experiment. Leaf Na concentrations were not affected by NaCl applications, averaging 42 mg·kg-1 across treatments. Conversely, leaf Cl concentrations increased significantly and cumulatively over time with salt additions, and ranged from 1.0 to 17.5 g·kg-1 (0.1 to 1.75%). Regression analyses revealed that average relative dry weight yields increased with leaf Cl concentrations up to 4.0 g·kg-1 (0.40%), but were depressed at higher concentrations.
Brian J. Boman, Mongi Zekri, and Ed Stover
Although citrus (Citrus spp.) is sensitive to salinity, acceptable production can be achieved with moderate salinity levels, depending on the climate, scion cultivar, rootstock, and irrigation-fertilizer management. Irrigation scheduling is a key factor in managing salinity in areas with salinity problems. Increasing irrigation frequency and applying water in excess of the crop water requirement are recommended to leach the salts and minimize the salt concentration in the root zone. Overhead sprinkler irrigation should be avoided when using water containing high levels of salts because salt residues can accumulate on the foliage and cause serious injury. Much of the leaf and trunk damage associated with direct foliar uptake of salts can be reduced by using microirrigation systems. Frequent fertilization using low rates is recommended through fertigation or broadcast application of dry fertilizers. Nutrient sources should have a relatively low salt index and not contain chloride (Cl) or sodium (Na). In areas where Na accumulates in soils, application of calcium (Ca) sources (e.g., gypsum) has been found to reduce the deleterious effect of Na and improve plant growth under saline conditions. Adapting plants to saline environments and increasing salt tolerance through breeding and genetic manipulation is another important method for managing salinity.
Raul I. Cabrera*
The azalea hybrids `Delaware Valley White' (`DVW') and `Hershey Red' (`HR') were grown in 7-L containers filled with a 4 sphagnum peat: 2 pine bark: 1 sand medium (v/v) and fertigated for 15 weeks with a complete nutrient solution supplemented with 0, 6 and 12 mm NaCl-CaCl2 (2:1 molar ratio). Regardless of salinity stress, `DVW' plants had dry weights and leaf areas significantly higher (by 24.7% and 10.2%, respectively) than in `HR' plants. Salinity, however, caused differential growth and quality responses between the hybrids. Growth in `DVW' plants decreased with salinity increases, with 22.6% and 32.4% reductions in total dry weight and leaf area, respectively, observed at 12 mm salt compared to controls. Conversely, `HR' plants exposed to 12 mm salt showed no differences in yield parameters with respect to the controls, whereas plants receiving 6 mm salt showed increases of 14.0% and 7.1% in total dry weight and leaf area, respectively, with respect to the controls. Plant quality, as assessed by visual symptoms of salt injury (“salt burn”), was significantly reduced by salinity increases in `DVW' plants, but was not affected in `HR' plants. While unaffected by salinity, leaf K status in `HR' plants was significantly lower than in `DVW', which showed increases in K concentration with salinity increases. Leaf Ca, Cl and Na concentrations increased with added salinity in both hybrids. The `DVW' plants, however, accumulated exceedingly higher Cl and Na concentrations (up to 3.33% and 5,650 mg·L-1 respectively) than in `HR' plants (up to 1.31% and 463 mg·L-1, respectively). Only the yield and quality of `DVW' plants were negatively and significantly correlated to increases in leaf Cl and Na concentrations.
Yueju Wang, Michael Wisniewski, Richard Meilan, Minggang Cui, Robert Webb, and Leslie Fuchigami
Ascorbate peroxidase (APX) plays an important role in the metabolism of hydrogen peroxide in higher plants, affording them protection against oxidative stress. We studied the effect of overexpressing a cytosolic ascorbate peroxidase (cAPX) gene—derived from pea (Pisum sativum L.)—in transgenic tomato plants (Lycopersicon esculentum L.). Transformants were selected in vitro using kanamycin resistance and confirmed by polymerase chain reaction (PCR) and northern analyses. An APX native-gel assay indicated that, in the absence of stress, APX activity in transgenic plants was several times greater than that measured in wild-type (WT) plants. Several independently transformed lines were propagated and evaluated for resistance to chilling and salt stress. After placing seeds at 9 °C for 5 weeks, percent germination was greater for seeds obtained from transgenic lines (26% to 37%) compared to the WT (3%). Plants from transgenic lines also had lower electrolyte leakage (20% to 23%) than WT (44%) after exposure to 4 °C. Visual assessment of transgenic and WT lines exposed to salinity stress (200 or 250 mm) confirmed that overexpression of APX minimized leaf damage. Moreover, APX activity was nearly 25- and 10-fold higher in the leaves of transgenic plants in response to chilling and salt stresses, respectively. Our results substantiate that increased levels of APX activity brought about by overexpression of a cytosolic APX gene may play an important role in ameliorating oxidative injury induced by chilling and salt stress.
B.E. Branham and D.W. Lickfeldt
With increasing pressure to reduce disposal of yard waste in landfills, many homeowners are seeking alternative methods for grass clipping disposal. When turf is treated with pesticides, the collected grass clippings become a potential source of injury to susceptible plants that come in contact with the clippings. In this study, grass clippings were collected at 2, 7, and 14 days after pesticide treatment from a turf treated with chlorpyrifos, clopyralid, 2,4-D, flurprimidol, isoxaben, or triclopyr. The clippings were used as a mulch around Lycopersicon esculentum Mill. (tomato), Phaseolus vulgaris L. (bush bean), Petunia ×hybrida Hort. Vilm.-Andr. (petunia), and Impatiens wallerana Hook. f. (impatiens). Beans were planted 4 weeks prior to mulching, whereas the other plants were grown in the greenhouse for 6 weeks and transplanted into the field 2 weeks prior to mulching. Clippings containing residues of clopyralid, 2,4-D, or triclopyr killed tomato, bean, and petunia plants when used 2 days after pesticide treatment (DAPT) and severely injured these same species when mulched 7 and 14 DAPT. Flurprimidol injured tomato, impatiens, and bean plants when present on mulch collected 2, 7, and 14 DAPT, but was not lethal. Flurprimidol slowed plant growth, caused darker green leaf color, and reduced flowering when mulched at 2 DAPT. Isoxaben injured tomato and bean plants when present on mulch used 2, 7, and 14 DAPT but was not lethal. Injury was not as severe in the second year of the study, indicating different environmental stresses and climatic conditions make predicting pesticide injury for all growing seasons difficult; however, grass clippings from a turf treated with herbicides or plant growth regulators should not be used for mulch around sensitive plants for at least 14 DAPT. Chemical names used: 0,0-diethyl O-(3,5,6-trichloro-2-pyridinyl) phosphorothioate (chlorpyrifos); 3,6-dichloro-2-pyridinecarboxylic acid, triethylamine salt (clopyralid); 2,4-dichlorophenoxyacetic acid, dimethylamine salt (2,4-D); α-(1-methylethyl)-α-[4-(trifluromethoxy)phenyl]-5-pyrimidinemethanol (flurprimidol); N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl]-2,6-dimethoxybenzamide and isomers (isoxaben); 3,5,6-trichloro-2-pyridinyloxy acetic acid, triethylamine salt (triclopyr).
Ana Bian and Dongming Pan
is important to understand the salt injury mechanism of salt stress in N. tazetta L. Most plants are sensitive to salt stress, and their growth is inhibited in saline environments ( Deinlein et al., 2014 ; Maser et al., 2002 ). Generally, plants