Wet Foliage Research Articles

A Facile Approach to Increasing the Foliage Retention of Pesticides Based on Coating with a Tannic Acid/Fe3+ Complex

The effective utilization of many conventional pesticide formulations is less than 30%, which can increase the environmental impact of these substances. This degree of waste could be reduced by improving the adhesion of pesticides to foliage. In the present work, a complex comprising tannic acid (TA) and Fe3+ ions was used to encapsulate azoxystrobin and avermectin water dispersible granule (WDG) formulations (termed Az-WDG-TA and Av-WDG-TA) to improve adhesion. The treated pesticides exhibited improved photostability as well as sustained continuous release behavior. The retention proportions of the Az-WDG-TA and Av-WDG-TA on cucumber and lettuce foliage were improved by more than 50%. The ability of solutions of these materials to wet foliage was also enhanced after coating, such that the toxicity of Av-WDG-TA to aphids and the antifungal activity of Az-WDG-TA to Fusarium oxysporum were increased by nearly 50%. Given the low cost of TA and Fe3+ compounds and the simple synthesis process, this method represents a promising means of producing foliage-adhesive pesticide formulations with increased retention and bioavailability.

Predicting leaf state effects on radiowaves based on propagation loss measurements

A new propagation model is proposed for estimating the attenuation of wireless communication signals in woodland environments. After rainfall or snowfall, the components of the woodland area become moist which degrades the received signal level. To take this into account, the model considers wet/dry states of the foliage, and its dependency on the operating frequency. The parameters of the propagation loss model are optimized using the least squares method. To demonstrate the validity and usefulness of the model, computed results are compared with measured data where excellent matching is observed. It is noted that not only the foliage and rainfall affect the propagation phenomenon, but also wet foliage condition after rainfall contributes to the fading of the wave.

Effects of wetting on the persistence of quiescent conidia of Isaria fumosorosea

Quiescent conidia of Isaria fumosorosea were submitted to various wetting–drying cycles under different regimes of temperature and air humidity. Germination and viability of conidia collected on cultures freshly host-passed (P2) were not affected at 25 °C during five cycles at increasing wet phase duration (2–12 h per daily cycle) under any moisture conditions (13–86% RH). Infectivity levels remained stable, but mortality was slightly postponed. In vitro-cultured inocula (P5) were significantly affected after only one cycle at higher air humidity (75 and 86% RH) and temperature (35 and 40 °C). The persistence of I. fumosorosea conidia suspended in water soluble extracts of leaf surfaces (corn and cabbage) confirmed the better persistence of P2 conidia and the relatively higher detrimental effect of lower air humidity conditions when combined with moderate temperatures. Quiescent conidia deposited in situ on potted plants of cabbage showed a higher persistence on wet foliage and on foliage submitted to wetting–drying cycles, than on dry foliage. These results underline that constraints prevailing in targeted environments and ecological fitness of fungal isolates have to be taken into account for assessing microbial control strategies.

Studies Regarding Biometric Characteristics of Lettuce (Lactuca sativa L.), Grown at Different Rates of Irrigation

Many vegetable species are shallow-rooted and sensitive to mild water stress. A possibility for improving water use is better management of water application, but that’s require information on detailed seasonal changes in crop growth and on root distribution and root extraction of soil water that is not currently available for most vegetable crops. In lettuce, where the harvested part of the plant is the photosynthetic leaf area, it is especially important to maintain optimal growth through the application of water and nutrients (GALLARDO et al, 1996). The experiments were made in bifactorial sequences, in spring of year 2006, placed in the vegetable field glasshouse, from USAMV Cluj-Napoca. The main purpose was to study the watering regime influence on the yield level and the quality of lettuce. The experiment included drip irrigation and microsprinkler irrigation, with three irrigation water levels (60, 70 and 80 % from activ humidity interval). Harvested plants from each variant were evaluated immediately according to yield, plant height, head diameter, leaf number and dry matter. Plant weight (g), head diameter (cm) and plant height (cm) were measured by caliper rule and calculated as the average of measured values. The average leaf number per plant was calculated by counting the leaves, and the dry matter amount was found after drying at 85 o C in 48 hours. Data show that differences due to water regime, irrigation method and the interaction between water regime and irrigation methods were highly significant for both, yield and water use efficiency. At high irrigation levels (80% AHI), yield were high (30 t/ha with dripline) and decreased significantly (23,2 t/ha with microsprinklers) at low irrigation levels (60% AHI). We can draw the conclusion that for lettuce culture in protected area, the best irrigation method is drip irrigation. The microsprinklers with special sprayer are not giving the best results in protected area, because of higher evaporation losses, higher humidity, the wet foliage which increases the potential for diseases, recording a percent of 20 % perished plants. The significant increases in dry matter were found as parallel to irrigation water deficit and the highest and lowest dry matter were found at 60% AHI irrigation level and 80% from AHI, respectively. This may be attributed to higher plant weight observed from 80% AHI treatment than those of deficit irrigation treatments. In other words, when the leaves were desiccated relative difference was bigger. Applying a different watering method for lettuce cultivated in protected areas, influences the plant growth, and so the production obtained. Developing the humidity condition from soil, that means any growing minimal level of watering applying with 10% from IUA caused a growing production. REFERENCES

FOLIAR ABSORPTION OF INTERCEPTED RAINFALL IMPROVES WOODY PLANT WATER STATUS MOST DURING DROUGHT

A large proportion of rainfall in dryland ecosystems is intercepted by plant foliage and is generally assumed to evaporate to the atmosphere or drip onto the soil surface without being absorbed. We demonstrate foliar absorption of intercepted rainfall in a widely distributed, continental dryland, woody-plant genus: Juniperus. We observed substantial improvement in plant water status, exceeding 1.0 MPa water potential for drought-stressed plants, following precipitation on an experimental plot that excluded soil water infiltration. Experiments that wetted shoots with unlabeled and with isotopically labeled water confirmed that water potential responded substantially to foliar wetting, that these responses were not attributable to re-equilibration with other portions of the xylem, and that magnitude of response increased with water stress. Foliar absorption is not included in most ecological, hydrological, and atmospheric models; has implications for interpreting plant isotopic signatures; and not only supplements water acquisition associated with increases in soil moisture that follow large or repeated precipitation events, but also enables plants to bypass soil water uptake and benefit from the majority of precipitation events, which wet foliage but do not increase soil moisture substantially. Foliar absorption of intercepted water could be more important than previously appreciated, especially during drought when water stress is greatest.

Intra‐storm evaporation as a component of canopy interception loss in dryland shrubs: observations from Fowlers Gap, Australia

AbstractInterception losses from the canopies of dryland plant taxa remain poorly understood, especially the relative contributions of intra‐storm and post‐storm evaporative losses. Employing a new measuring apparatus, this study uses low‐intensity simulated rain, matched to the properties of local rain, to explore interception processes in bluebush shrubs at an Australian dryland site. Five shrub specimens were exposed to simulated rain for 60–90 min. Experiments were repeated at three rainfall intensities (10, 15, and 20 mm h−1). Canopy evaporation was found from the difference between the flux of water delivered to the shrub and the flux of throughfall, once equilibrium had been established. The results show that evaporation from the wet foliage during rain proceeds at an average rate of 3·6 mm h−1. This figure is for relatively cool spring‐season conditions; evaporation rates in hot summer conditions would be larger. Intra‐storm evaporation is shown to exceed post‐rain evaporation from interception storage on the shrubs, and this differentiates dryland shrub interception processes from those of the better‐studied wet forest environment. Implications of the high dryland shrub canopy evaporation rates for aspects of dryland ecology are highlighted. Copyright © 2007 John Wiley & Sons, Ltd.

An Observation of Foliage-bathing by an Orange-breasted Falcon (Falco deiroleucus) in Tikal, Guatemala

I observed a pair of Orange-breasted Falcons (Falco deiroleucus) in Tikal, Guatemala, on 30 December 2003 and 1 January 2004. I observed the birds flying through wet foliage as a means of bathing, which has not been described previously for this species. During a morning with light rain, an adult falcon took off from a perch, flew low over the forest canopy, and appeared to crash intentionally into the wet, upper foliage of emergent trees before returning to its perch. I observed three repetitions of this behavior.

Near-ground channel measurements over line-of-sight and forested paths

Near-ground radio-wave propagation is of interest for emerging military applications such as battlefield sensor networks and for wireless communication between dismounted soldiers. Narrowband and wideband channel measurement results at 300 and 1900 MHz are presented for near-ground propagation, characterising the effect of antenna heights, radiation patterns and foliage environments. An additional set of channel measurements was performed to study the effect of rain on near-ground propagation at 1900 MHz in a forest environment. Measured power–delay profiles indicate significant multipath propagation with the multipath components becoming stronger relative to the direct path for decreasing antenna heights. In the LOS measurements, the RMS delay spread decreased with the use of directional antennas and increasing antenna heights, and increased with distance. This effect was not evident in the forest measurements, suggesting a larger angle spread of the multipaths. Measurement results indicate that leaves and wet foliage do not contribute significantly to the scattering of radio waves. Foliage effects are more significant at 1900 MHz than 300 MHz. Results from near-ground sensor measurements demonstrate that path-loss varies inversely with the square of the receiving antenna height, as in the plane-Earth and Egli models.

BREEDING PEACH FOR NARROW LEAF WIDTH

Mature peach leaves are typically about 4 x 16 cm, with a width/length ratio of about 25%. A narrow leaf seedling, selected by Wayne Sherman (Univ. of Florida, Gainesville), was hybridized at USDA-Byron with adapted commercial varieties. Early generation hybrids produced small, irregular-shaped fruit. After 5 generations, current selections are approaching commercial fruit standards in size, color, firmness, and attractiveness. Narrow-leaf trees are often noticeably more open than standard trees. This leaf type may be useful in standard- or high-density plantings to enhance spray penetration, to speed drying of wet foliage to reduce disease, to improve light penetration and photosynthetic efficiency for greater fruit size and red color, and to make the fruit more visible to speed picking. Inheritance studies indicate that the narrow-leaf character is at least partially dominant and is expressed in some F1 seedlings of crosses with wild-type parents. The exact inheritance remains unclear as the ratios obtained to date do not fit common inheritance patterns. Progeny vary in leaf width with ratios of width/length generally ranging from 10-25%. The most extreme seedling has leaves up to 28 cm long and 1 cm wide, and although it is not fruitful, it may have ornamental value.

Sensitivity tests with a biosphere model based on BATS, suitable for coupling with a simple climatic model

A biosphere model based on the Biosphere Atmosphere Transfer Scheme (BATS) suitable for coupling with a simple climate model is described. In this model the equations of BATS are adapted to the energy flux formulations of the statistical-dynamical model developed by Franchito & Rao (Climatic Change, 22:1-34; 1992). In this work the land surface model was run to perfom sensitivity tests regarding the behaviour of the model variables with respect to prescribed model parameters and contrasting vegetation types, such as evergreen broadleaf forest and short grass. The results show that the soil surface temperature increases with the decrease of the fractional area of vegetation cover due to the lower surface solar radiation flux absorption in both types of vegetation. As the water interception increases the wet foliage air layer prevents the evaporation of the soil water, so that there is an increase of the ground surface temperature. The surface temperature is lower in the forest than in the case of short grass due to the surface roughness effect. In the case of dry soil the available energy increases with the increase of the fractional area of vegetation cover because the latent heat flux increases quickly and the sensible heat flux decreases slowly. In the situation of fully wet soil the available energy dependence on the interception is reduced due to the effect of water evaporation at the ground surface that increases the latent heat flux, even if the interception is small or nil. A factor <FONT FACE="Symbol">z</font> is inserted in the expression that gives the fractional area of the leaf canopy cover by water in order to take into account the effect of the part of vegetation predominantly porous. The lower values of <FONT FACE="Symbol">z </font>give better results regarding the component terms of the evapotranspiration. However, the total flux of water vapor to atmosphere does not change with <FONT FACE="Symbol">z</font>. Sensitivity tests are made with respect to the factor Y introduced in the expression of the water vapor flux to the atmosphere in order to adjust the partitioning of the available energy into latent and sensible heat. The results show that the latent (sensible) heat increases (decreases) with the increase in Y. Although the variation of Y modifies the Bowen’s ratio there is no change of the evapotranspiration partitioning into its components.

Meteorological method based on wet foliage to determine areas at high risk of fungal epidemics

The occurrence of fungal diseases is closely linked to specific atmospheric conditions affecting the life cycle of the fungus. Popular beliefs as well as scientific knowledge are in agreement on the effect of high temperature and moisture on fungal epidemics. The presence of a film of water on a plant, during an uninterrupted number of threshold hours is in many cases a necessary, and sometimes sufficient condition for fungal infection to develop. In this paper, we present a method to estimate the sequence of hours of wet and dry vegetal surface. Conventional hourly meteorological data are used. The accuracy of this method has been studied over an ideal sunflower field located in Balcarce (Buenos Aires, Argentina) with promising results.

A gas exchange system to study the effects of leaf surface wetness on the deposition of ozone

Abstract A leaf chamber system has been developed for measuring the uptake of ozone (O 3 ) by whole plant leaves artificially wetted with dew or raindrops. Tests showed negligible amounts of O 3 being lost on internal walls of the chamber, and good heat and mass transfer characteristics without the use of internal mixing fans. The system enables easy and accurate determination of pollutant uptake by wet and dry foliage. Measurements of O 3 fluxes to individual leaves indicate that leaf surface wetness, either in the form of a dew layer or raindrops, on the adaxial surface of hypostomatous red maple leaves, enhances the deposition of O 3 . The increased O 3 deposition is ascribed mainly to the presence of compounds in aqueous form that readily scavenge O 3 , with a lesser additional contribution from decreased stomatal resistance to O 3 diffusion.

The influence of climatic conditions around the time of spraying isoproturon on the subsequent injury to barley

SummaryWinter barley cv. Igri was grown in pots, either outside under cover, in a glasshouse or under controlled conditions and treated post‐emergence with isoproturon. There was a linear relationship between the subsequent weight of plants treated with 2.5 kg a.i./ha and either evaporation from a water surface between 2–7 days post spraying or cumulative temperature between sowing and spraying. The relationship between subsequent weight of plants treated to the foliage only with 5 kg a.i./ha and cumulative temperature between sowing and spraying varied between years 1984–86. The post spraying environment had the major influence on subsequent activity of isoproturon at 2.5 kg a.i./ha applied overall to barley under controlled conditions. There was a greater reduction in CO2 exchange in plants grown after treatment under high compared to low relative humidity. When isoproturon at 5 kg a.i./ha was applied to barley plants with wet foliage, plants were slower to recover their initial rate of photosynthesis when kept wet for 24 h as compared with 11 h or when allowed to dry after treatment. Photosynthesis was decreased to a lesser extent under the same post spray conditions by 2.5 than by 5 kg a.i./ha and reduction was greater and recovery of photosynthesis slower in plants grown inside compared to outside.

Relationship between Environmental Conditions and Nocturnal Activity of the Terrestrial Frog, Leiopelma archeyi

The number of frogs emerging at night in a field population of the terrestrial frog Leiopelma archeyi was examined in relation to environmental conditions. Frogs emerge at or about dusk from retreat sites on the forest floor, climbing up to 2 m high in the vegetation before returning to their retreats at dawn. Emergence is strongly and positively correlated (P 0.1). Frogs which emerged on nights when the vegetation was dry probably suffered little water loss by evaporation, because of the high humidities and cool temperatures which prevailed in the forest habitat. Experimentally dehydrated L. archeyi rehydrated rapidly from wet foliage, increasing from 92 to 99% of original body weight over 4 hr. Although emergence of most L. archeyi was limited to times of high moisture availability, rapid water uptake through ventral skin allowed this species to utilize sources of water which were only present ephemerally. The availability of moisture is widely assumed to limit the temporal and spatial activity of permeable-skinned amphibians in natural habitats, and thus their ability to carry out important ecological activities such as feeding and reproduction (Keen, 1984). When confronted with a water shortage, many amphibians remain in or rapidly seek moist microenvironments (e.g., Heatwole, 1962; Jaeger, 1971; Degani and Warburg, 1978). However, the Puerto Rican frog, Eleutherodactylus coqui, is considered an exception (Pough et al., 1983). Eleutherodactylus coqui inhabits subtropical rainforests and emerges by night to engage in foraging, territorial defence, and reproductive activity. Despite losing water by evaporation, individuals continue to emerge on dry nights for at least the first 7 days without rain, occupying the same arboreal perches as they do on wet nights. Behavioral adjustments are made on dry nights to minimize evaporative water loss (EWL). By day, coquis return to their retreat sites and make up for water lost overnight by absorbing moisture from their retreat site substrates (van Berkum et al., 1982; Pough et al., 1983). Leiopelma archeyi Turbott is a member of the anatomically primitive family Leiopelmatidae and is restricted to mountain ranges on or in the vicinity of the Coromandel Peninsula, New Zealand (Bell et al., 1985). Like E. coqui, L. archeyi is terrestrial, inhabiting high rainfall forest and Present Address: Department of Zoology, Victoria University of Wellington, Private Bag, Wellington, New Zealand. usually remaining in cool, humid retreat sites by day (Cree, 1986). However, apart from reports that L. archeyi (Turbott, 1942) or leiopelmatid frogs in general (Bell et al., 1985) climb trees and vegetation on wet nights, little is known about factors affecting emergence of this species. My study examines the relationship between environmental conditions and nocturnal activity of L. archeyi in a field population, and demonstrates the ability of experimentally dehydrated L. archeyi to make use of a natural moisture source (wet vegetation) for rehydration.

Basic Data on Air Requirements for Cleaning Christmas Trees

A basic study of Christmas tree cleaning with an air blast was conducted. Virginia pine Christmas trees were suspended in a large diameter air stream. Cleaning variables included air velocity, retention time in the air stream, and wet versus dry foliage. Very good cleaning was achieved with an air velocity of 121 km/h (75 mph) and a retention time of 15 s. Wet foliage had no effect on cleaning.

Pseudomonas corrugata . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Pseudomonas corrugata . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Lycopersicon esculentum . Also isolated from symptomless roots of Medicago saliva . DISEASE: Tomato pith necrosis. The pith is discoloured brown to dark brown and may show cavities, especially in the lower parts of the stem. External symptoms frequently seen include chlorosis of upper leaves, sometimes a brown to black external stem lesion where the pith is most badly affected, bacterial exudate from leaf scars, pruning and other wounds, and on older plants prolific development of adventitious roots on the stems in areas where the pith is most badly affected. GEOGRAPHICAL DISTRIBUTION: South Africa, New Zealand (cultures at CMI), Denmark (62, 6), England, Germany (East 60, 5559; West 61, 6591), Italy (S. Sardinia 63, 1960), USA (CA 62, 2155; F 62, 3656; PA 59, 919 on Lucerne). The distribution is probably much more widespread than these records show. TRANSMISSION: The bacterium is probably common in the environment. It has, for example, been isolated from mains water which was being used to irrigate an affected crop. It is probably also spread from plant to plant by man in cultural operations. The disease is favoured by high humidity or wet foliage and high nitrogen levels in the soil; conditions that favour soft plant growth that is most susceptible.

ALDICARB ON GREENHOUSE CHRYSANTHEMUMS IN ONTARIO: EFFICACY FOR CONTROL OF LIRIOMYZA TRIFOLII (BURGESS) (DIPTERA: AGROMYZIDAE) AND RESIDUES IN FOLIAGE

AbstractIn two field tests, larvae of Liriomyza trifolii (Burgess) were not controlled by aldicarb (Temik 10G) at three times the recommended rate when applied to soil, dry foliage, or wet foliage of chrysanthemums (cv. White Marble) in Ontario. A second treatment of aldicarb 3 weeks after the first did not prevent the increase in leafmining. Assessment of the top 10 leaves at harvest showed no significant differences in numbers of mines greater than 2 cm between check and treated plots. Residues of aldicarb and its degradation compounds, aldicarb sulfoxide and aldicarb sulfone, were detected by capillary gas chromatography with thermionic specific detection. Substantial residues (&gt; 100 μg/g as total residues), particularly of aldicarb sulfoxide, were found within the 1st week after treatment, but dissipated rapidly in upper leaves by day 7 after the first aldicarb application. Lower leaves, however, maintained residue levels at a constant level for a 3-week period following the first and second applications. Residue levels on lower leaves were consistently higher after wet-foliage application of aldicarb than after soil application.

Evaluation of evapotranspiration and canopy resistance: An alternative combination approach

This paper gives a preliminary outline of a suggested different type of combination method for evaluating evapotranspiration and surface resistance, with brief discussion of its application to vegetated surfaces. In the well known Penman-Monteith (P-M) combination method the surface temperature and humidity are eliminated by combining the bulk aerodynamic and heat budget relationships. In the method proposed here the surface values are again eliminated, but here by combining the bulk aerodynamic and Bowen ratio relationships (the ‘B-B’ method). Whereas the P-M method may be applied using climatological data alone if desired, the B-B method is applicable only when the appropriate measurements are made including the Bowen ratio. The B-B method may be applied over short time intervals (e.g. 20 min) if required. The B-B formulation is more sensitive to the surface characteristics — bulk transfer coefficient and effective surface resistance — than is the P-M. Therefore it is suggested that for vegetated surfaces the main application of the B-B method would be in establishing empirically these surface characteristics for various types of vegetation at different stages of growth and under different conditions. In this role the capability of evaluation over small time intervals would be advantageous in studies with changing conditions, e.g. with the soil drying out, with evaporation from wet foliage, or with changing illumination.

The influence of plant communities upon the hydrology of catchments

This paper reviews some of the present scientific knowledge about the water yield from catchments that vary in their land use. Afforested catchments yield less runoff because the evapotranspiration from them is larger than from catchments not in forest. The evaporation of rain water held upon the wet foliage of trees proceeds at a faster rate than would the transpiration if the leaves were dry. Since the interception store can be 2 mm and is often more than this in dense forests, the interception loss can probably account for the observed yields from afforested catchments of up to 200 mm yr −1 less than from (say) grassland, where rainfall is >1 m yr −1. The soil water deficit that deep-rooted, perennial plants can create is also likely to be larger than that caused by annual pastures and cereal crops. Although it is hard to find reliable data for comparative purposes, it is likely that a soil water deficit of 250 mm each year could be created by evergreen forest stands and 180 mm each year by annuals, in the climatic regions of southern Australia where the rainfall is 700 mm yr −1 or more. These figures themselves would imply a yield of 70 mm yr −1 less from afforested land, in runoff of surface water, or recharge of groundwater.

Effect of Four Foliage-Applied Herbicides on Field Horsetail (Equisetum arvense)

Amitrole (3-amino-s-triazole), asulam (methyl sulfanilylcarbamate), glyphosate [N-(phosphonomethyl)glycine], and fosamine [ethyl hydrogen (aminocarbonyl)phosphonate] were effective in reducing the amount of shoot regrowth from field horsetail (Equisetum arvenseL.) 3 months after treatment. The order of effectiveness was amitrole &gt; glyphosate &gt; asulam &gt; fosamine. The advantage of adding surfactant to the spray formulation or applying herbicides to wet foliage was rate dependent for all herbicides except fosamine. Spray retention was increased by application to wet foliage and by the inclusion of surfactant in the formulation. Spray retention increased as spray volume and plant size increased and as plant growth became prostrate. A scanning electron microscope study of the shoot surfaces showed an abundance of silica-containing structures and the presence of epicuticular wax. Certain surfaces of the scale leaves did not have these characteristics, indicating that redistribution of spray to these areas may result in greater penetration with subsequent increases in herbicide performance.