Leaf Burn Research Articles

Chemical characterisation of particle emissions from burning leaves

Particulate matter emissions (PM10) from open-air burning of dry leaves were sampled and analysed for a series of organic and inorganic species, including carbon fractions, anhydrosugars, humic-like substances (HULIS), water-soluble ions, metals and organic trace components. The study was performed to investigate whether open-air burning of leaves in rural areas is a potential source of high amounts of unexplained organic matter (OM) in ambient PM. Results of the carbon analysis indicated that the amount of OM, more than 90% of emitted PM10, is significantly higher in smoke from leaves than from wood burning [Schmidl, C., Marr, I.L., Caseiro, A., Kotianova, P., Berner, A., Bauer, H., Kasper-Giebl, A., Puxbaum, H., 2008. Chemical characterization of fine particle emissions from wood stove combustion of common woods growing in mid-European Alpine regions. Atmospheric Environment 42, 126–141, till now considered as the main combustion source of organic PM used in source apportionment. While the proportion of total carbon (TC), 67% of PM10, is very similar to that in wood smoke, the make-up of the total carbon is different. In wood smoke, levels of elemental carbon (EC) equivalent to soot, of around 20% were found, however in leaf smoke EC was very low, between 0 and 10% depending on the analytical methodology. In addition chemical markers were identified that permit the discrimination of wood smoke from leaf smoke in ambient PM samples. In particular the levels of anhydrosugars, sugar alcohols, PAH and n-alkanes in leaf smoke differ significantly from those in wood smoke. The ratios of levoglucosan to galactosan and benzo[a]pyrene to tetracosane differ by an order of magnitude between smoke of leaf burning and that of typical mid-European firewood (Schmidl et al., 2008). Furthermore sugar alcohols were found in notable concentrations in leaf burning samples, which were not found in wood smoke. Complete chemical profiles for leaf burning as a particulate matter source are presented here, including organic trace compounds to be used in source apportionment studies either by the chemical mass balance (CMB) or the macrotracer approach.

Urea Foliar Fertilization Affects Onion Weight and Nutrient Content

ABSTRACT Foliar application is used to supply fertilizers to developing crops. This method provides flexibility to the producer in their application. This research was undertaken to investigate effects of foliar application of urea on onion (Allium cepa L.), cv. Salamony, in Syria. Four levels of urea, 0, 2,000, 3,500, and 5,000 mg·L−1, were evaluated. Plants were treated with 16.6 mL/plant of urea three times, at 3-day intervals, starting 26 days after planting. Salamony can positively respond to up to 5,000 mg·L−1 of urea without hazard of leaf burn, and bulb fresh and dry weights increased as urea concentration increased. Nitrogen (N), phosphorus (P), potassium (K), and total cation contents of bulbs were increased, but magnesium (Mg), calcium (Ca), and sodium (Na) contents were not affected by treatment. The 5,000 mg·L−1 treatment proved to be the most effective in increasing bulb fresh and dry weights and increasing mineral uptake.

Can crops be irrigated with sodium bicarbonate rich CBM deep aquifer water? Theoretical and field evaluation

A simulation modelling exercise, followed by field trials was carried out to assess the suitability of sodium bicarbonate (NaHCO 3) rich water obtained from dewatering for extraction of methane gas from coal beds in the Limpopo Province, Republic of South Africa. This water has a very high EC of 750 mS m −1, which according to FAO water quality guidelines would suit only salt tolerant crops. Modelled crop growth at a leaching fraction (LF) of 23% using the Soil Water Balance (SWB) model gave root zone salinity (EC e) between 857 and 981 mS m −1, and a 90% potential crop yield. In the field trials, barley, Italian ryegrass and Bermuda grass were successfully grown in a loamy sand soil without leaf burn and toxicity problems, but cotton foliage was scorched when sprinkler irrigated. Drip emitter discharge rate decreased from 3.99 ± 0.15 to 3.5 ± 0.19 l h −1, suggesting that clogging will be problematic with micro irrigation. SWB gave a good estimation of the suitability of this NaHCO 3 rich water in the theoretical assessment, which was similar to the experimental findings. SWB, therefore, is a useful tool for assessing the suitability of NaHCO 3 deep aquifer water for irrigation of agricultural crops.

The effect of water stress and rootstock on the development of leaf injuries in grapevines irrigated with saline effluent

Deficit irrigation is increasingly being practiced in water-limited areas to overcome water scarcities. Although, this practice reduces yield losses, there is limited information currently available on how this practice can affect crops when the irrigation water contains elevated levels of salts. An experiment was set up to investigate salt uptake and distribution and salt tolerance of potted Soultanina vines grafted on different rootstocks (41B, 1103P, 110R) and irrigated with effluent containing relatively high concentrations of salts and fresh water at different fractions of evapotranspiration (0.50, 0.75 and 1.00ET). Irrigation with recycled water induced the development of leaf burns, which were more intense in 1998 despite the lower leaf-Na and -Cl content. This may have been due to the more severe water deficit and/or to the more adverse climatic conditions which prevailed during that season. Decreasing the irrigation level induced the development of leaf burns causing only minor changes to leaf-Na or -Cl content. Differences in salt uptake, accumulation and distribution were observed among the rootstocks investigated in this work, suggesting that differences exist in the mechanisms regulating salt uptake and distribution in the shoot. Despite these differences, a distinct superiority in terms of salinity tolerance among rootstocks was only observed at the 0.50ET irrigation level, where vines grafted on 41B developed earlier and more acute leaf burns than the other rootstocks. These findings suggest that leaf salt content alone it is not to classify genotypes according to their tolerance to salinity and that salinity-induced damage is linked with prevailing environmental conditions. Furthermore, it can be inferred that grapevines have additional mechanisms to cope with salt stress which may counteract differences in salt uptake and accumulation in the shoot.

The use of sunn hemp as green manure intercropped with taro

An experiment was carried out in Magé, Rio de Janeiro State, Brazil, to evaluate the performance of taro (Colocasia esculenta) intercropped with sunn hemp (Crotalaria juncea), used as green manure. A randomized blocks design with four replicates was used and the soil of the field plots was classified as Haplic Gleysol. Treatments consisted of taro (1) intercropped with unpruned sunn hemp, (2) intercropped with sunn hemp cut at soil level, (3) intercropped with sunn hemp pruned at its mid-height, and (4) in monoculture. The taro was planted in double rows spaced by 1.0 m. The planting furrows had a space of 0.5 m, with rhizomes placed at every 3.0 m. The experimental plot consisted of four 3.0 m rows and the useful area corresponded to the five central plants in each of the two central rows. The sunn hemp was sown in parallel lines in the spaces between the taro double rows, 120 days after planting the taro. When the sunn hemp was cut at soil level, an accumulation of 211 kg ha-1 of N was observed. Besides this, the sunn hemp's biomass promoted the cycling of an average 17 kg ha-1 of P, 85 kg ha-1 of K, 151 kg ha-1 of Ca, and 27 kg ha-1 of Mg. Worth mentioning, it represented also a deposition of 6.85 Mg ha-1 of dry substance. Even when pruned at its mid-height, the sunn hemp still provided 60% of nutrients relatively to the treatment in which it was cut at soil level. In addition to the nutrient supply, the use of taro intercropped with sunn hemp cut at soil level or pruned at mid-height represented efficient alternatives for controlling the spontaneous vegetation and for reducing taro leaf burning by solar radiation, without compromising the yield of taro. In all intercropping systems, taro plants had a larger leaf area and were taller than plants in monoculture.

Using Trifloxysulfuron with Glyphosate for Cotton Weed Control

Field studies were conducted during the 2002 thru 2004 growing seasons at two locations in the south-central Texas cotton-production region to evaluate trifloxysulfuron and trifloxysulfuron plus prometryn in combination with either S-metolachlor or glyphosate or both for weed control and cotton response. Cotton leaf burn (13 to 19%) was noted in 2002 at one location with trifloxysulfuron plus prometryn applied late POST-directed (LPDIR). Herbicide combinations that included trifloxysulfuron controlled barnyardgrass, hemp sesbania, yellow nutsedge, Palmer amaranth, smooth pigweed, ivyleaf morningglory, pitted morningglory, and smellmelon at least 80% in most instances. Glyphosate applied early POST over-the-top (EPOTT) and mid-POST over-the-top (MPOTT) at 0.84 kg ai/ha followed by trifloxysulfuron plus prometryn at 1.1 kg ai/ha applied LPDIR controlled the above-mentioned weeds plus Texas panicum at least 94%. No other herbicide systems provided effective control (greater than 79%) of Texas panicum. Higher...

Modeling Leafhopper Nymphs in Temperate Vineyards for Optimal Sampling

Abstract Cicadellids (Homoptera: Cicadellidae) are occasional pests of vineyards in temperate areas, and unchecked populations can build up to high densities to cause leaf burn followed by defoliation and yield loss. Therefore, an optimal sampling scheme would allow determination of risk at minimal cost. Because the development of leafhopper nymphs and feeding injury is closely tied to temperature, a model driven by the accumulation of degree-days was developed to predict leafhopper cumulative abundance at 5, 50, and 95% levels in vineyards. The model was based on 22 data sets collected over 7 yr in three vineyards in southern Quebec. It was based on the cumulative abundance of nymphs of the eastern grape leafhopper; the grapevine leafhopper; the threebanded leafhopper; the Virginia creeper leafhopper; and Erythroneura vitifex Fitch. The lower threshold temperature for development was 8°C. Paired t-tests and the forecasting efficiency confirmed the validity of the model. The model indicated that monitorin...

Sporophyte and Gametophyte Generations Differ in their Thermotolerance Response in the Moss Microbryum

Actively growing post-embryonic sporophytes of desert mosses are restricted to the cooler, wetter months. However, most desert mosses have perennial gametophytes. It is hypothesized that these life history patterns are due in part to a reduced thermotolerance for sporophytes relative to gametophytes. Gametophytes with attached embryonic sporophytes of Microbryum starckeanum were exposed whilst desiccated to thermal episodes of 35 degrees C (1 hr), 55 degrees C (1 hr), 75 degrees C (1 hr) and 75 degrees C (3 hr), then moistened and allowed to recover for 35 d in a growth chamber. All of the gametophytes survived the thermal exposures and produced protonemata, with the majority also producing shoot buds. Symptoms of gametophytic stress (leaf burning and discoloration of entire shoots) were present in lower frequencies in the 55 degrees C exposure. Sporophyte resumption of growth and maturation to meiosis were significantly negatively affected by thermal treatment. Not a single sporophyte exposed to the two higher thermal treatments (75 degrees C for 1 h and 75 degrees C for 3 h) survived to meiosis, and those sporophytes exposed to 75 degrees C that survived to the post-embryonic phenophase took significantly longer to reach this phase. Furthermore, among the thermal treatments where some capsules reached maturity (35 degrees C and 55 degrees C), maternal shoots that produced a meiotic capsule took longer to regenerate through protonemata than maternal shoots aborting their sporophyte, suggestive of a resource trade-off between generations. Either (1) the inherent sporophyte thermotolerance is quite low even in this desert moss, and/or (2) a gametophytic thermal stress response controls sporophyte viability.

An evaluation of foliar nitrogen and zinc applications to macadamia

The efficiency and effectiveness of foliar nitrogen (N) applications as urea to macadamia leaves were investigated in field experiments at Alstonville, New South Wales. The first experiment (August 2000) evaluated the effect of 1–8% urea solutions on the evidence of leaf burn. A 2% urea solution produced negligible leaf burn (1% leaves with lesions) whereas the incidence of leaf burn increased with urea concentration; 20% of leaves were affected with an 8% urea solution. In the following month, a second experiment was conducted using a 2% urea solution that was painted onto both sides of leaves to measure N uptake efficiency. The urea was enriched with the stable isotope 15N, which allows a direct measure of urea uptake, a common method for tracing plant N uptake. Leaves were sampled after 3 and 6 days, and cellulose acetate was then applied to remove urea adhering to the surface of leaves. Leaves adjacent to urea-treated leaves were also sampled to account for any transport out of treated leaves. The experiment was repeated in September 2001. In 2000, a mean of 31% of the urea was absorbed by the mature leaves and this increased the N content by 2.2%. In 2001, a mean of 38% of the urea was absorbed by the mature leaves and this increased N content by 1.9%. Leaves from part of a large mature macadamia tree were stripped to provide an estimate of leaf biomass. From this, the increase in leaf N uptake for a mature orchard was calculated to be 3.98 kg/ha in 2000 and 4.57 kg/ha in 2001. The efficiency of application and hence leaf N uptake from a commercial spray would be expected to be lower than that of the present study. Commercial foliar urea applications are unlikely to meet the N requirements of a productive macadamia orchard. In a separate study, the efficiency of zinc (Zn) fertiliser as soil (5–20 g Zn/m2 canopy ground area) and foliar applications were examined at a mature commercial orchard near Alstonville on a Ferrosol soil. In August 2001, a 2% solution of zinc sulfate heptahydrate was thoroughly applied to the canopy of trees using a backpack misting machine and mature leaves were sampled 4 weeks later. Non-sprayed control trees were also sampled. Cellulose acetate was applied to sampled leaves to remove foliar-applied Zn adhering to the surface of leaves. The leaf Zn concentrations were increased (P<0.05) from 11 to 52 mg/kg 4 weeks after foliar Zn application. Sprayed leaf Zn concentrations were stable 18 weeks later, and flush leaves that emerged after spray application had similar (P>0.05) Zn concentrations to control leaves 12 months later indicating that little if any remobilisation of Zn had occurred over these periods. Soil Zn application had no effect (P>0.05) on leaf Zn concentrations 1 and 2 years after application. The effectiveness of a commercial foliar Zn application was evaluated in September 2001 using a low set orchard sprayer and a 1% Zn solution. After 4 weeks, leaf Zn concentrations were increased from 12 to 26 mg/kg. Foliar Zn applications can be recommended to increase leaf Zn concentrations in macadamias despite evidence in the literature for only 1% uptake efficiency.

Evaluation of Treated Effluent as an Irrigation Source for Landscape Plants

Abstract Treated effluent from the Hampton Roads Sanitation District (HRSD) Virginia Initiative Plant (VIP) was evaluated in 2000 and 2001 as an irrigation source for landscape plants. Landscape plants common to eastern Virginia were installed in raised beds and overhead irrigated at the rate of 2.5 cm (1 in) per week for five months. Aesthetic quality ratings, and soil and water analyses, were conducted monthly. Aesthetic quality ratings were lower on certain plants irrigated with treated effluent in both years of the study. Damage appeared to result from foliar contact by irrigation water high in dissolved salts. Soil tests showed salt accumulation in the planting soil. Damage that occurred on plants irrigated with treated effluent was species specific and included leaf burn, chlorosis, defoliation, stunting, and death. All symptoms were consistent with and typical of salt damage. Salt concentrations in this treated effluent were too high to allow use of this water as an overhead irrigation source for many landscape plants without further treatment or dilution. Irrigation with treated effluent should be based on landscape species composition, local climate conditions, and irrigation method.

(450) Drought Responses of Ornamental Herbaceous Perennials

We investigated drought responses of Echinacea purpurea, Gaillardia aristata, Lavandula angustifolia, Leucanthemum ×uperbum `Alaska', Penstemonbarbatus`Rondo', and Penstemo×mexicali `Red Rocks' established in a 10-gal pot-in-pot system in northern Utah. Plants were irrigated at frequencies of 1, 2, or 4 weeks between June and Sept. 2004. Osmotic potential, gas exchange, visual quality, leaf area, and dry biomass were assessed. In a confined root zone, P. barbatusshowed the greatest tolerance to drought, avoiding desiccation by increasing root: shoot ratio and decreasing transpiration as water became more limiting. Plants maintained high visual quality throughout the study and experienced little wilt, burn, or dieback. However, P. barbatus above-ground biomass was reduced by 15% for the 2-week treatment and by 40% for the 4-week treatment. Alternatively, G. aristata and L. superbum displayed drought avoidance mechanisms, dying back when water was limiting and resprouting after they were watered. Above-ground biomass declined by 50% and 84% for G. aristata and 47% and 99% for L. superbum, respectively, for the 2- and 4-week treatments. Root mass was affected similarly for both species. However, transpiration remained high for all treatment levels. Leaf burn and reduction in above- and below-ground biomass were also evident for E. purpurea at the 2- and 4-week treatments, but results were not as pronounced as for G. aristata and L. superbum. Overall, P. barbatusexhibited the greatest drought tolerance while maintaining an acceptable appearance. G. aristata, contrary to expectations, did not exhibit drought tolerance with a confined rooting volume, suggesting that it avoids drought in landscapes by means of deep rooting.

(98) Impact of Selected Insecticides on Gas Exchange, Vegetative and Floral Development, and Overall Quality of Gerbera (Gerbera jamesonii var. `Festival Salmon')

This research focused on the influence of insecticides on gas exchange, chlorophyll content, vegetative and floral development, and overall plant quality of gerbera (Gerbera jamesonii var. `Festival Salmon'). Insecticides from five chemical classes were applied weekly at 1× and 4× the recommended concentrations. Insecticides used were: abamectin (Avid® 0.15 EC), acephate (Orthene® Turf, Tree & Ornamental Spray 97), bifenthrin (Talstar® Nursery Flowable), clarified hydrophobic extract of neem oil (Triact® 70), and spinosad (Conserve® SC). Phytotoxicity occurred in the form of leaf chlorosis on all acephate treatments, with the greatest damage occurring at the 4× concentration. Photosynthesis and stomatal conductance were significantly reduced in plants treated with neem oil extract. Plants treated with the neem oil extract (1× and 4×) flowered later and had reduced growth [lower shoot dry mass (DM) and total DM]. Plants that received 4× the recommended concentration of neem oil extract had reduced leaf area, thicker leaves (lower specific leaf area), higher leaf chlorophyll content, and reduced flower production, as determined by flower number and flower DM. Plants treated with acephate 4× concentration were the lowest quality plants due to extensive phytotoxicity (leaf burn), which also reduced photosynthesis. The highest quality plants were treated with spinosad and abamectin due to zero phytotoxicity and/or no thrips damage (thrips naturally migrated into the greenhouse). The control plants and plants treated with bifenthrin 1× were not marketable due to thrips damage; however, plant growth characteristics and gas exchange were not statistically different.

(65) Evaluation of Curcuma as Potted Plant and Cut Flower

Sixteen accessions of Curcuma germplasm and several selected accessions of Curcuma were evaluated for use as potted plants or as cut flowers. Curcuma alismatifolia Gagnep. and C. thorelii Gagnep. `Chiang Mai Snow' met standards for cut flower and pot plant use, respectively. Furthermore, C. parviflora Will. `White Angel' proved to be a good selection for potted plant production. Optimum storage temperatures of rhizomes were studied in relation to greenhouse forcing and carbohydrate changes. It is recommended to store rhizomes at 25 to 30 °C after harvest for 2 to 3 months to break dormancy. Plants of C. parviflora `White Angel' flowered in 50 to 89 days and C. `CMU Pride' flowered in 104 days after potting, and were acceptable as potted plants. Plants of C. alismatifolia flowered 96 to 133 days after potting with floral stem length suitable for use as a cut flower. A high level of boron or manganese may cause the burn at the margin of the leaves (marginal leaf burn) observed on old leaves of `CMU Pride' at flowering. The level of ethanol-soluble fructose, glucose, and sucrose in elongated rhizomes with emerged short shoots of Curcuma was higher than the level in rhizomes and increased as storage temperatures increased. Accelerated leaf emergence may be associated with the increase in the glucose and fructose content. Based on the similar morphological characters between C. thorelli `Chiang Mai Snow' and C. parviflora `White Angel', identification of Curcuma accessions is required in future studies.

Resistance of Shrub and Groundcover Roses to Black Spot and Cercospora Leaf Spot, and Impact of Fungicide Inputs on the Severity of both Diseases

Abstract Reaction of selected shrub and ground cover roses to black spot, Cercospora leaf spot, and powdery mildew, as well as the impact of fungicide inputs on the control of the above diseases, was assessed from 1999 through 2003 in a simulated landscape planting in Brewton, AL. Chlorothalonil at 1.25 g ai/liter was applied at 2- and 4-week intervals from mid-March until October to randomly selected plants in each replicate. An unsprayed control was also included in each replicate. Although black spot was the predominate disease observed, a number of rose selections suffered from objectionable Cercospora leaf spot-induced leaf spotting and premature defoliation. Few mixed outbreaks of black spot and Cercospora leaf spot on a single selection were seen. In all years, significant differences in the reaction of rose selections to black spot and Cercospora leaf spot were noted. Of the roses damaged by black spot, the least leaf spot and defoliation were noted on the unsprayed Ice Meidiland®, Mystic Meidiland®, Red Cascade™, ‘Hansa’, ‘Pink Grootendorst’, ‘Pink Pet’, and to a lesser extent Carefree Wonder™ and Pearl Sevillana™. In a residential planting, monthly applications of chlorothalonil or other recommended fungicide would be needed to protect the above rose selections from a destructive black spot outbreak. ‘Betty Prior’, Bonica®, Cherry Meidiland®, First Light™, Kent™, Jeepers Creeper™, ‘Livin’ Easy™, Lilian Austin™, ‘Nearly Wild’, ‘Nozomi’, Butterfly rose, Ralph's Creeper™, Raven™, Royal Bonica™, ‘Sea Foam’, Sevillana™, and Sweet Chariot™ were susceptible to black spot. While black spot did not appreciably damage Carefree Delight™, Flower Carpet®, White Flower Carpet®, Fire Meidiland®, Fuchsia Meidiland®, Happy Trails™, ‘Petite Pink Scotch’, Polar Ice™, R. wichurana, The Fairy™, and ‘Therese Bugnet’, considerable Cercospora leaf spot development occurred on all of the above rose selections. Of these roses, Polar Ice™, Fuchsia Meidiland®, and Fire Meidiland® exhibited the highest resistance to Cercospora leaf spot and may not require any fungicide inputs to maintain plant health and vigor. Magic Carpet™ and Knock Out™ roses, which were susceptible and resistant to black spot, respectively, as well as Flower Carpet®, and White Flower Carpet® appeared to be poorly adapted to the hot and sometimes dry summer weather patterns of South Alabama. In nearly all years, chlorothalonil gave better control of both diseases when applied on a 2-week than on a 4-week schedule. Significant chlorothalonil-induced leaf burn was seen on First Light™, Flower Carpet®, ‘Hansa’, Happy Trails™, Magic Carpet™, Mystic Meidiland™, ‘Nozomi’, and Raven™. Consistent powdery mildew development was found only on ‘Therese Bugnet’ and to a lesser extent on Red Cascade™ and ‘Petite Pink Scotch’. Canopy spread of the roses that were heavily damaged by black spot and Cercospora leaf spot often was often reduced in size when compared with that of adjacent chlorothalonil-treated plants of the same selection. In contrast, little if any increase in growth was obtained with fungicide inputs for the more disease resistant rose selections.

Rosemary Cultivar Ontogeny Affects Success as Potted Christmas Tree Shaped Topiary

Greenhouse production of rosemary (Rosmarinus officinalis L.) as small potted Christmas tree topiaries for holiday sales has become necessary for many companies marketing to large retail outlets. Topiaries must be sheared multiple times to obtain an acceptable Christmas tree shape. Cultivars vary in physical attributes, suggesting that they may respond differentially to mechanical shearing during production. This study assessed sixteen rosemary cultivars for their potential as potted Christmas tree shaped topiaries. Beginning July 2001, rosemary plants derived from vegetative propagation of shoot tips were provided high fertility and maximum light in a greenhouse. From August to October, plants were pruned monthly for a total of three shearing events. The crop was considered mature on the targeted market date of 5 Dec. Final plant quality was visually assessed using a 1 to 5 scale that accounted for taper, plant-to-pot ratio, canopy density, foliage quality, and overall appeal, with one point being removed for each factor not meeting industry expectations. The cultivars varied in their performance as Christmas tree shaped topiaries with most being unacceptable due to minimal basal branching or excessive leaf burn that negatively impacted shape, taper, and aesthetics. Six of the cultivars, `Taylor's Blue', `Herb Cottage', `Joyce DeBaggio' (Golden Rain), `Shady Acres', `Rexford' (Rex), and an unnamed clone, were suitable for commercial use having visual ratings ranging from 3.8 to 4.5. These cultivars had equally healthy foliage with little damage. `Taylor's Blue', `Shady Acres', `Joyce DeBaggio' (Golden Rain), the unnamed clone, and `Herb Cottage' had foliar damage ratings ranging from 3.3 to 3.8 and were not significantly different from the most healthy cultivars, `Logee White' (Thinleaf White), `Salem', and `Hill Hardy', all of which had mean ratings of 4.0. These cultivars should be examined for additional attributes that may enhance their performance as Christmas tree shaped topiaries.

Foliar Burn and Wheat Grain Yield Responses Following Topdress-Applied Nitrogen and Sulfur Fertilizers

The most common fertilizer sources for topdress nitrogen (N) applications to winter wheat (Triticum aestivum L.) in Virginia are a urea ammonium nitrate (UAN) solution (30-0-0) or a UAN solution with added sulfur (S) (UAN-S; 20-0-0-4). However, there are some concerns regarding leaf burning following foliar N applications, particularly at later growth stages. An experiment was conducted from 1999 through 2002 to evaluate and quantify foliar burn associated with various topdress-applied N sources, any subsequent effect on wheat grain yield, and any yield response to added S. Ammonium nitrate (AN; 34-0-0), UAN, UAN-S, and ammonium sulfate (AS; 21-0-0-24) were topdress-applied at either GS 30 or 32. Following the GS 30 and 32 foliar applications, digital images were obtained from each plot and pixel analysis was used to estimate the percentage of foliar burn. At GS 30, foliar burn increased with increasing N rate with no difference in the percentage of burn being observed between sources. At GS 32, foliar burn again increased with increasing N rate; however, UAN-S resulted in significantly greater foliar burn than UAN at both N rates. Despite the increased foliar damage that occurred when UAN-S was topdress-applied at GS 32, there was no reduction in grain yield compared with UAN or either of the soil-applied sources at either growth stage. Although there was no evidence of a grain yield response to added S in this study, many soil types common to the Coastal Plain of Virginia are likely to lack sufficient S for optimum winter wheat production.

Efficacy of Acidic Electrolyzed Water Ice for Pathogen Control on Lettuce

Acidic electrolyzed water (AcEW) was used as frozen AcEW (AcEW-ice) for inactivation of Listeria monocytogenes and Escherichia coli O157:H7 on lettuce. AcEW-ice was prepared from AcEW with 20, 50, 100, and 200 ppm of available chlorine by freezing at −40°C and generated 30, 70, 150, and 240 ppm of chlorine gas (Cl2), respectively. The AcEW-ice was placed into styrene-foam containers with lettuce samples at 20°C for 24 h. Although AcEW-ice generating 30 ppm Cl2 had no effect on L. monocytogenes cell counts, AcEW-ice generating 70 to 240 ppm of Cl2 significantly (P < 0.05) reduced L. monocytogenes by ca. 1.5 log CFU/g. E. coli O157:H7 cell counts were reduced by 1.0 log CFU/g with AcEW-ice generating 30 ppm of Cl2. AcEW-ice generating 70 and 150 ppm of Cl2 reduced E. coli O157:H7 by 2.0 log CFU/g. Further significant reduction of E. coli O157:H7 (2.5 log CFU/g) was demonstrated by treatment with AcEW-ice generating 240 ppm of Cl2. However, treatment with AcEW-ice generating 240 ppm of Cl2 resulted in a physiological disorder resembling leaf burn. AcEW-ice that generated less than 150 ppm of Cl2 had no effect on the surface color of the lettuce. AcEW-ice, regardless of the concentration of the emission of Cl2, had no effect on the ascorbic acid content in the lettuce. The weight ratio of lettuce to AcEW-ice required was determined to be over 1:10. The bactericidal effect of AcEW-ice appeared within the first 2 h. The use of AcEW-ice provides simultaneously for low temperature storage and inactivation of bacteria.

Canopy Separation and Defoliation for Dry-on-the-vine (DOV) Raisins on Traditional Trellises

Pruning efficiency, fruitfulness, and yield and quality of raisins of `Thompson Seedless' (Vitis vinifera L.) grapevines subjected to several canopy separation and defoliation treatments for DOV raisin production were evaluated. Canopy separation treatments, tested in vineyards at Easton, and at the Kearney Agricultural Center (KAC), Parlier, Calif., were as follows; horizontal canopy separation with vine sections of fruiting or renewal zones (Peacock), horizontal canopy separation with vine sections of fruiting zones of one vine adjacent to renewal shoots of the next vine (wave), or non-separated (control). Defoliation treatments included burning or blowing leaves (Easton), application of concentrated solutions of calcium ammonium nitrate or Etherel to leaves (KAC), or no defoliation (both vineyards). Canopy separation treatments did not affect berry size, soluble solids, or raisin yield. Vines subjected to Peacock training had more cluster layers than vines subjected to wave training, at Easton, and more cluster layers than vines subjected to control training at KAC. Canopy separation reduced harvest pruning time by 20% at Easton, but not at KAC. No treatments affected raisin moisture at Easton but, at KAC, raisins of vines trained in the Peacock style had 10% higher moisture contents at harvest than raisins of wave or control vines. Vines subjected to conventional training and leaf blowing had about 40% higher “B and better” raisin grades than vines with separated canopies that were not defoliated, and about 30% higher grades than vines with conventional training and leaf burning. However, raisins of vines subjected to blowing had about 60% more mold than raisins of non-defoliated vines. Defoliation treatments at KAC did not affect any variables measured.

Insecticides from Five Chemical Classes Differentially Affect the Plant Growth and Development of Chrysanthemum (Dendranthema grandiflora Tzvelev var. Charm)

This research focused on the influence of insecticides on plant growth, gas exchange, rate of flowering, and chlorophyll content of chrysanthemum (Dendranthema grandiflora Tzvelev cv. Charm) grown according to recommended procedures for pot plant production. Five insecticides were applied at recommended concentrations at three different frequencies: weekly (7 days), bi-weekly (14 days), or monthly (28 days). A separate treatment was applied weekly at 4× the recommended concentration. Insecticides used were: acephate (Orthene®) Turf, Tree &amp; Ornamental Spray 97), bifenthrin (Talstar®) Flowable), endosulfan (Thiodan®) 50 WP), imidacloprid (Marathon®) II), and spinosad (Conserve®) SC). Phytotoxicity occurred in the form of leaf burn on all acephate treatments, with the greatest damage occurring at the 4× concentration. Photosynthesis and stomatal conductance were influenced primarily by the degree of aphid and/or spider mite infestation—except for acephate and endosulfan treatments (weekly and 4×), which had reduced photosynthesis with minimal insect infestations. Plants receiving imadacloprid monthly had the greatest leaf dry mass (DM). Plants treated with acephate had lower leaf and stem DM with bi-weekly and 4× treatments. Spinosad treatments at recommended concentrations had reduced stem DM, in part due to aphid infestations. The flower DM was not significantly different among treatments. There were treatment differences in chlorophyll content as measured with a SPAD-502 portable chlorophyll meter.

Yield and insect injury in leafhopper (Empoasca fabae Harris and Empoasca kraemeri Ross &amp; Moore) infested dry beans in Ontario and Colombia

Recombinant inbred lines derived from a cross between a leafhopper-susceptible bean (Phaseolus vulgaris L.), Berna Dutch brown and leafhopper-resistant selection EMP 419 were examined for resistance to the leafhopper species Empoasca abae (Harris) and Empoasca kraemeri Ross and Moore in Ontario, Canada and Colombia, South America, respectively. In both Ontario and Colombia there were significant positive correlations of visual injury scores with percent reductions in seed count, seed yield and seed weights. Leafhopper injury symptoms were significantly correlated with degree of stunting in Ontario, while only leaf burn scores were correlated with stunting in Colombia. Nymph counts were significantly and positively correlated with leaf curl scores in Ontario but not in Colombia, despite significant rank correlations of leaf burn scores and leaf curl scores between these locations. In a second experiment comparing the effects of E. fabae nymph infestations on set of 23 resistant and 5 susceptible recombinant inbred lines (RILs), the latter lines were infested by significantly fewer nymphs. Possible resistance mechanisms to E. fabae and E. kraemeri are discussed. Key words: Potato leafhopper, resistance insect, antixenosis, bean (navy), tolerance