Foliar Spray Deposition Research Articles

Leaf Sample Size for Pesticide Application Technology Trials in Coffee Crops

Plot size, sample sufficiency, and number of repetitions are factors that affect the experimental errors or residuals and the expression of true differences among treatments. The objective of this study was to determine, using statistical models, the appropriate sample size for application technology experiments in coffee crops through the evaluation of foliar spray deposition and soil runoff in the ground-based application of pesticides. In the first stage, we determined the quantity of leaves per set and the volume of the solution for washing the leaves and extracting the tracer. We analyzed the variability between the coefficients of variation (CVs) of the amount of tracer extracted in two droplet classes (fine and coarse), for the different parts of the plants, and for the different quantities of leaves per set that were organized into intervals of five leaves (1-5, 6-10, 11-15, and 16-20). Less variability was found in the intervals with 10 leaves per set and using 100 mL of extraction solution. In the second stage, a field experiment was conducted using an entirely randomized design with 20 plots: 10 sprayed with fine droplets and 10 with coarse droplets. In each plot, 10 sets (samples) with 10 leaves each were collected from the upper and lower canopy of the coffee trees. Moreover, 10 Petri dishes were placed per plot and collected after application. Based on the results of the spray deposition (mass of tracer extracted per cm2 of leaf), we determined the optimal sample size using the maximum curvature and maximum curvature of the coefficient of variation methods. Higher variabilities were related to the targets that are more difficult to reach. Thus, this study determined an optimal sample size between five and eight sets of leaves for spray deposition, and four to five Petri dishes for soil runoff.

What happens when pesticides are solubilised in binary ionic/zwitterionic-nonionic mixed micelles?

HypothesisSurfactants have been widely used as adjuvants in agri-sprays to enhance the solubility of pesticides in foliar spray deposits and their mobility through leaf cuticles. Previously, we have characterised pesticide solubilisation in nonionic surfactant micelles, but what happens when pesticides become solubilised in anionic, cationic and zwitterionic and their mixtures with nonionic surfactants remain poorly characterised. ExperimentsTo facilitate characterisations by SANS and NMR, we used nonionic surfactant hexaethylene glycol monododecyl ether (C12E6), anionic sodium dodecylsulphate (SDS), cationic dodecyltrimethylammonium bromide (DTAB) and zwitterionic dodecylphosphocholine (C12PC) as model adjuvant systems to solubilise 3 pesticides, Cyprodinil (CP), Azoxystrobin (AZ) and Difenoconazole (DF), representing different structural features. The investigation focused on the influence of solubilisates in driving changes to the micellar nanostructures in the absence or presence of electrolytes. NMR and NOESY were applied to investigate the solubility and location of each pesticide in the micelles. SANS was used to reveal subtle changes to the micellar structures due to pesticide solubilisation with and without electrolytes. FindingsUnlike nonionic surfactants, the ionic and zwitterionic surfactant micellar structures remain unchanged upon pesticide solubilisation. Electrolytes slightly elongate the ionic surfactant micelles but have no effect on nonionic and zwitterionic surfactants. Pesticide solubilisation could alter the structures of the binary mixtures of ionic/zwitterionic and ionic/nonionic micelles by causing elongation, shell shrinkage and dehydration, with the exact alteration being determined by the molar ratio in the mixture.

Foliar deposition and coverage on young apple trees with PWM-controlled spray systems

Pulse width modulation (PWM) technology is recently introduced into orchard air-blast sprayers to achieve precision applications of plant protection products and reduce risks to the environment and ecosystems. Field tests in a two-year old, multi-row apple orchard were conducted to study the foliar spray deposition generated by three systems attached to an air-blast orchard sprayer: 1) a manually-PWM-controlled spray system producing a constant-rate application (Manual-PWM), 2) a laser-guided PWM-controlled intelligent spray system producing a variable-rate application (Laser-PWM), and 3) the same laser-guided spray system with disabled PWM control producing a constant-rate application (Disabled-PWM). The capability of applying sprays on multiple tree rows beyond the first target row was also quantitatively evaluated for the three systems. Test results showed that the Manual-PWM and Disabled-PWM produced greater spray deposits and coverage with over-sprayed potentials on the first target row trees than Laser-PWM. However, spray coverage results indicated that Laser-PWM provided higher uniformity across the tree canopy and a stronger relationship between spray deposits and coverage for all the rows than other two systems. Moreover, Laser-PWM used 67% and 76% less spray volume than Manual-PWM and Disabled-PWM, respectively. Test results also demonstrated that spray deposit densities on trees discharged from all three spray systems exceeded thresholds for effective fungicide and insecticide applications (proposed by pesticide manufacturers), not only in the first target row but also second and further downstream rows. A single spray pass from each of the three systems could provide adequate spray deposits and coverage on the two-year old young trees in the first two rows, thereby offering opportunities to save pesticides and reduce labor costs. Future field biological tests to verify the efficacy of these spray systems are necessary to confirm these hypotheses.

Influence of Nonpermanent Netting on Foliar Spray Deposition, Insect Pest Prevalence, and Production of ‘Nadorcott’ Mandarin (Citrus reticulata)

This study aimed to determine the effects of different types of nonpermanent netting (NPN) on foliar spray deposition, insect pest prevalence, and production and fruit quality of ‘Nadorcott’ mandarin (Citrus reticulata) trees in a commercial orchard at Citrusdal (lat. 32 32′31″S, long. 19 0′42″E), Western Cape, South Africa. The deposition quantity (FPC%) of foliar spray volumes of 3500, 7000, or 15,000 L·ha−1 was greater for leaves of control trees compared with leaves treated with NPN during summer (January) (8.8 vs. 6.1; P = 0.0055) and winter (June) (4.8 vs. 3.1; P = 0.0035). Deposition uniformity (CV%) was better for control leaves during summer (64.9 vs. 75.2; P = 0.0062) and winter (59.6 vs. 80.5; P = 0.0014), and deposition quality (ICD%) was better during winter (79.4 vs. 84.2; P = 0.0393). There were no differences in FPC%, CV%, and ICD% for fruit when foliar spray volumes of 3500 and 15,000 L·ha−1 were used for the control and NPN treatment groups during winter. However, with a foliar spray volume of 7500 L·ha−1, fruit from the control treatment group had greater FPC% (19.3 vs. 6.1; P = 0.0262), CV% (70.3 vs. 50.9; P = 0.0484), and ICD% (57.1 vs. 79.9; P = 0.0157). There were no differences in macronutrient concentrations between the leaves of trees subjected to control and NPN treatments, but leaf zinc (<81%; P = 0.0317) and iron (<78%; P = 0.0041) concentrations were lower with the NPN treatment. During short NPN treatments, fruit yield was reduced by ≈37% compared with that after control treatment, and longer NPN treatments had no effect on fruit yield. The reduction in fruit yield with NPN was not related to the effects of NPN on foliar spray deposition or to lower leaf micronutrient concentrations. The lower fruit yield during short NPN treatments was most likely caused by fruit drop that was exacerbated by the removal of the NPN. In the long NPN treatment group, fruit damage caused by sunburn was reduced by 17%, but the outer canopy fruit experienced increased wind damage or scarring. Except for the lower titratable acidity content with the shortest NPN treatment and the higher Brix°:TA ratio with two NPN treatments, NPN did not impact other fruit quality attributes. The use of NPN excluded male wild false codling moths (Thaumatotibia leucotreta) (FCM) males; however, it was still possible to capture a very small amount of mass-released sterile FCM and wild fruit flies under the NPN.

Effects of inoculation method on efficacy of wettable powder and oil dispersion formulations of Beauveria bassiana against Colorado potato beetle larvae under low-humidity conditions

ABSTRACTThe effects of inoculation method on efficacy of two formulations of Beauveria bassiana strain GHA against Colorado potato beetle larvae were investigated. Under dry greenhouse conditions, ca. 58% mortality was observed among second-instar larvae exposed directly to sprays of B. bassiana conidia, whereas mortality among larvae exposed to similarly treated foliage (either leaf dorsal or ventral surfaces) was <10%. Mortality was ca. 64% among larvae exposed to both direct sprays and foliar spray deposits. Equivalent rates of mortality were observed among larvae treated with a clay-based wettable powder versus an emulsifiable oil-based formulation of B. bassiana conidia; however, this was observed despite application of an approximately 40% greater dose of WP-formulated conidia, indicating greater efficacy of the emulsifiable oil formulation. These results suggest that, under dry conditions, potato beetle larvae do not readily acquire an effective dose of conidia from treated foliage and that development of improved application technologies to more effectively target the larvae may ultimately prove more beneficial than development of formulations with greater foliar persistence.

Foliar spray deposition in a “tendone” vineyard as affected by airflow rate, volume rate and vegetative development

The objective of this study was the evaluation of the effect of airflow rate and volume rate on foliar spray deposition in a “tendone” vineyard using an air-assisted sprayer with two counter-rotating fans and anterior intake. Experimental tests were carried out considering two airflow rates (2.43 and 5.71 m3 s−1), two volume rates (335 and 625 L ha−1) and keeping the forward speed constant (1.1 m s−1). To take into account the effect of vegetative development of the vineyard, experiments were replicated in two phenological stages (full flowering and berry touch), characterised by different Leaf Area Indices (2.21 and 5.83). The sprayer was calibrated using a patternator purposely designed for “tendone” vineyards, assuming the vineyard Leaf Area Index (LAI) pattern as a reference.Sprayer calibration was accomplished achieving a close correlation between LAI pattern and the quantity of liquid intercepted by the patternator (coefficients of linear correlation ranged from 0.95 to 0.99, all significant at p < 0.05). Measurements on vines showed that volume rate did not affect foliar spray deposition at either phenological stage, whereas airflow rate had an opposite effect at the two phenological stages. At full flowering, the increase in airflow rate produced a significant decrease in foliar deposit (from 0.986 to 0.693 μL cm−2 on the most exposed vegetation, −30%); on the contrary, at the berry touch growth stage the increase in airflow rate produced a significant increase in foliar deposits (from 0.339 to 0.484 μL cm−2, +43%).

Spray deposition in “tendone” vineyards when using a pneumatic electrostatic sprayer

The objective of this study was to evaluate the effect of electrostatic charge on foliar spray deposition in an Apulian “tendone” vineyard using an innovative pneumatic electrostatic sprayer. The sprayer was fitted with nozzles that linked the pneumatic atomization of the liquid, obtained using compressed air, to the electrostatic induction charge, thereby producing a stream of charged fine droplets. Furthermore, the sprayer was designed for low volume treatments, and the experimentation was carried out during a phenological stage with high leaf density to evaluate the performance of the machine under particularly challenging operative conditions.The sprayer was studied at three forward speeds (4, 5, and 6 km h−1), and gave poor deposition inside the canopy, whether or not the electrostatic system was activated. Forward speed did not significantly affect the mean foliar spray deposition, whereas activation of the electrostatic system significantly increased the deposit only on the layer of foliage nearest to the sprayer (lower layer), but had no effect on deposition on the layer of foliage inside the canopy (upper layer). The ratio between the deposits on the two layers (lower:upper) was 6.5:1 when the electrostatic system was switched off, and 9.0:1 when it was switched on.However, this behaviour may allow targeted treatments on grapes, such as with Plant Protection Products (PPP) or bio growth stimulants. Furthermore, the small droplets produced by the machine are suitable for table grape protection because the droplets do not mark the grapes, which would reduce the quality of the product and its commercial value.

Effects of adjuvants on deposition efficiency of fenhexamid sprays applied to Chardonnay grapevine foliage

Adequate spray deposition on susceptible grapevine tissue is an essential requirement for effective chemical control of economically important diseases, such as grey mould, powdery mildew and downy mildew. The objective of this study was to evaluate the potential of some agricultural adjuvants to improve foliar spray deposition. Deposition quantity and quality was assessed by means of a spray assessment protocol using fluorometry, photomicrography and digital image analyses. The visual droplet rating technique developed by G Furness, Australia, was also included in initial assessments. Both assessment protocols showed that spray deposition quantity increased with increasing spray volume applications of 27 l ha −1 to 581 l ha −1 with a motorised backpack mistblower, but decreased at 698 l ha −1, possibly due to run-off. Addition of selected spray adjuvants at 526 l ha −1 volume demonstrated improved deposition quantity and quality. Agral 90 (ethoxylated alkylphenol), BB5 (acidifier), Nu-film-P (terpene oil), and Solitaire (silicone/plant oil) significantly improved deposition on upper and lower leaf surfaces compared with the fenhexamid-only and water sprayed control. Break-thru S240 (organosilicone) and Villa 51 (alkylpolyethylene glycol ether) did not improve deposition quantity, although remarkably better deposition quality was obtained. An adjuvant concentration effect (within the registered concentration range) was evident at spray volumes of 502 l ha −1, especially those retained on the upper leaf surfaces. Agral 90 and Nu-film-P effected significant improvement of spray deposition at the higher concentrations (18 ml and 50 ml hl −1, respectively), but not at the lower concentrations (6 ml and 20 ml hl −1, respectively). Solitaire improved deposition at the lower concentration tested (50 ml hl −1), whereas reduced deposition at the higher concentration (100 ml per hl −1) was attributed to excessive spray run-off. No significant improvement of spray deposition was observed for both concentrations tested with Villa 51 (50 and 100 ml hl −1). Spray mixtures with adjuvants Agral 90 and Solitaire yielded similar deposition values at 500 l ha −1 compared with the fenhexamid-only control at 720 l ha −1, but reduced deposition at the higher spray volume, possibly due to spray run-off. This study clearly demonstrated the potential of adjuvants to improve deposition quantity and quality, but highlights the necessity to match adjuvant concentrations and application volumes on the spray target to achieve maximum spray deposition.

Influence of Spray Volume on Spray Deposition and Coverage within Nursery Trees

Abstract Information on better utilizing airblast sprayers to achieve high pesticide spray application efficiency in nursery tree production is needed. Foliar spray deposition and coverage at different heights inside crabapple tree canopies were investigated for a conventional airblast sprayer operating at four different application rates ranging from 230 to 900 liters/ha [24 to 94 gallons per acre (GPA)]. Deposition on the ground at various distances from the sprayer was also measured at the 700 liters/ha (73 GPA) application rate. Foliar deposition and coverage on targets below 2.6 m (8.5 ft) inside tree canopies increased as the application rate increased, but the increase in the coverage was much lower than the deposition. For trees taller than 2.6 m (8.5 ft), the sprayer could not deliver uniform spray deposition and coverage across the tree height. The portion of trees below 2.1 m (6.9 ft) was well covered by the spray deposits with 230 liters/ha (24 GPA) application rate while higher application rates resulted in over spray application. Less than 30% of total spray volume was deposited on target trees while over 34% of the total spray volume was lost on the ground. The tree-row volume method should include foliage density and tree-row gaps to avoid excessive estimation of spray application rates for nursery tree crops.

Volume, Speed, and Distribution Technique Effects on Poinsettia Foliar Deposits

The influence of spray volume, application speed, and distribution technique on spray deposits found on greenhouse poinsettias was investigated. Foliar spray deposits were measured on upperside and underside leaf surfaces in the top and bottom canopy locations. Five different application techniques were used to treat 12-week-old, bench-grown, greenhouse poinsettias. High-volume, high-pressure techniques were used to simulate variations on conventional application practices. Air-assisted, electrostatically charged sprays were used to simulate low volume, hand-directed, application techniques. A mechanical aerosol generator was used to simulate low volume applications generated at a single point and intended to fill the greenhouse with a fog. Spray deposition was measured by spectral analysis of food dye tracer. Spray deposits were higher in the top canopy location and on the upperside leaf surfaces. The lowest spray deposits were found in the bottom canopy location and on the undersides of those leaves. Hand-directed distribution techniques resulted in significantly higher spray deposits compared to the whole-room fogging spray distribution technique. Slower applications that doubled the total application time and that were made using the same spray volume as higher speed applications nearly doubled underside leaf deposits. The greatest variability in spray deposits was found with higher application speeds and reduced volume applications made through the high pressure handgun. It was observed that the higher spray volumes increased spray deposits through redistribution resulting from run-off and touching leaf surfaces.

Development and assessment of a mathematical model to predict foliar spray deposition under laboratory track spraying conditions

AbstractA mathematical model based on Young's equation of adhesion of liquids to solid surfaces has been developed to predict foliar spray deposition under track‐spraying conditions. The model incorporates the physical nature and morphological characteristics of the plant leaf surface and the physical properties of the spray solution. It was tested using experimental spray deposition measurements on four different plant species and an artificial target of glass rods with an array of forty‐eight solutions varying systematically in composition and properties. The morphological factors and regression coefficient of the model were calculated by a least‐squares multiple‐regression analysis of the observed spray deposition. The physical natures, wettabilities, of the target surfaces were estimated from contact angle measurements. The physical properties of the spray solutions, drop sizes and dynamic surface tensions were measured by a Malvern 2600 HSD particle size analyser and the maximum bubble pressure method respectively. Drop sizes were approximately constant through the series of solutions though dynamic surface tensions varied and form an important term in the model.The spray depositions predicted by the model were plotted as response surfaces against solution composition and compared with those from the observed spray depositions. Agreements were high (explained variances, wheat, 96.4%; green foxtail, 98.6%; pea, 98.9%; sugar beet, 98.6%; glass rods, 99.4%), giving confidence that the model had been correctly formulated.An explanation for the varying abilities of different plants to capture different volumes of spray solutions can now be expressed in qualitative and quantitative terms. Further validation of the model is in progress.