Spray Regimes Research Articles

SPRAY IN CROSS FLOW OF A ROTARY ATOMIZER

This paper presents an experimental investigation of fuel sprays generated by a rotary atomizer exposed to a cross flow of air. The effects of two variables, the rotational speed and cross-flow velocity, on the droplet sizes were studied. The rotary atomizer was driven at speeds up to 15,000 rpm with a fuel flow rate of 15 kg/h and cross flow from 10 to 150 m/s. For any given rotational speed, the fuel droplet sizes decreased as the air cross flow increased, reaching an almost constant value of about 8 μm at 150 m/s cross-flow velocity. At cross-flow velocities less than about 50 m/s, the fuel droplet sizes decreased as the rotational speed increased. However, at a cross-flow velocity greater than 100 m/s, the fuel droplet sizes did not changed significantly as the rotational speed increased. Of the two variables studied, each influenced the droplet size differently in a certain cross-flow velocity region. The rotational speed influenced the droplet size at relatively low cross-flow velocity. By exceeding a cross-flow velocity of 75 m/s, the dynamic effect of high-speed cross flow became dominant. This effect can be generalized to the Weber number based on the orifice diameter and the non-dimensional droplet size. In this correlation, the following three distinct spray regimes were identified according to the Weber number based on orifice diameter: rotation dominant, intermediate, and cross flow dominant.

Regimes of spray formation in gas-centered swirl coaxial atomizers

Spray formation in ambient atmosphere from gas-centered swirl coaxial atomizers is described by carrying out experiments in a spray test facility. The atomizer discharges a circular air jet and an axisymmetric swirling water sheet from its coaxially arranged inner and outer orifices. A high-speed digital imaging system along with a backlight illumination arrangement is employed to record the details of liquid sheet breakup and spray development. Spray regimes exhibiting different sheet breakup mechanisms are identified and their characteristic features presented. The identified spray regimes are wave-assisted sheet breakup, perforated sheet breakup, segmented sheet breakup, and pulsation spray regime. In the regime of wave-assisted sheet breakup, the sheet breakup shows features similar to the breakup of two-dimensional planar air-blasted liquid sheets. At high air-to-liquid momentum ratios, the interaction process between the axisymmetric swirling liquid sheet and the circular air jet develops spray processes which are more specific to the atomizer studied here. The spray exhibits a periodic ejection of liquid masses whose features are dominantly controlled by the central air jet.

Evaluation of contact fungicide spray regimes for control of late blight (Phytophthora infestans) in southern Ethiopia using potato cultivars with different levels of host resistance

Late blight is an important disease of potato in Ethiopia, causing up to 100% loss in susceptible cultivars. In this study, two putatively resistant cultivars of relatively recent introduction (Jalenie and Gudenie) and a widely grown susceptible cultivar (White Flower) were evaluated for late blight severity and yield under five different contact fungicide (mancozeb) regimes and in unsprayed plots. Trials were carried out at two major potato production locations in southern Ethiopia: Awassa and Kokate, located at 1700 and 2156 meters above sea level, respectively. Greater disease pressure occurred at Awassa but the three cultivars performed consistently based on relative disease severity levels at the two locations. While White Flower was assigned a susceptibility score of 8 (highly susceptible) in both sites, Jalenie had scores between 1 and 0, and Gudenie had scores of 3 and 4, in Awassa and Kokate, respectively. With Jalenie, one application of contact fungicide was sufficient in both trials, while for Gudenie, two sprays appeared more appropriate as little or no gain was clear with three or more sprays. With the susceptible White Flower, four sprays were beneficial but little benefit was evident with the fifth spray.

Voltage effects on the nanoelectrospray characteristics in fully voltage-controlled atomisation of gold nanocolloids

The voltage effects on fully voltage-controlled nanoelectrospraying of aqueous gold nanocolloids were investigated. In the nanoelectrospray using 30 μm nozzle, with an increasing of voltage two stable spray regimes of pulsating and cone-jet mode were clearly observed by a combination of current measurement and fast imaging technology. In this nanoelectrospray uniquely determined by the electrical field voltage the current–voltage characteristics were analysed and evaluated based on an equivalent circuit method. At high field in cone-jet regime all the equivalent resistances derived by fitting appear close to a value of 0.53 ± 0.03 GΩ, showing independence to the conductivity of the nanocolloids. In low field pulsating regime a high pulsation frequency up to 100 kHz with relatively stable current pulse was exhibited in all the gold nanocolloids. A linear relationship between the DC components in the pulsating current and the voltage was found and the DC equivalent resistance obtained from the fitting varies between 0.90 and 1.47 GΩ. A strong correlation between the pulsating properties and the conductivity of the colloids was identified.

EFFECT OF GIBBERELLIC ACID ON THE PERSISTENCE OF CERTAIN PESTICIDES ON/IN GRAPE FRUITS

Recommended application was done by spray regime for two pesticides, namely diniconazole, fenitrothion and a plant growth regulator (gibberellic acid) and their mixtures. Their residues were determined after different successive treatments in and on grape fruits in two consecutive years. The initial deposits of the fungicide diniconazole when used alone were 0.49 and 0.50 ppm for 2006 and 2007, respectively. While the initial deposits of fenitrothion reached to 11.35 and 11.19 ppm for the same interval, respectively. Initial deposits of the plant growth regulator gibberellic acid were 30.52 and 30.42 ppm for the same period, respectively. After mixing the tested pesticides and the plant growth regulator, the initial deposits loss reached 38.77 and 42.0 % for diniconazole, 43.08 and 48.16 % for fenitrothion and 6.88 and 7.00 % for gibberellic acid for the same seasons, respectively. A significant degradation was recorded with the mixture of the two tested pesticides and plant growth regulator compared with that occurred when pesticide was used alone at the two studied seasons.

Regime Transition in Electromechanical Fluid Atomization and Implications to Analyte Ionization for Mass Spectrometric Analysis

The physical processes governing the transition from purely mechanical ejection to electromechanical ejection to electrospraying are investigated through complementary scaling analysis and optical visualization. Experimental characterization and visualization are performed with the ultrasonically-driven array of micromachined ultrasonic electrospray (AMUSE) ion source to decouple the electrical and mechanical fields. A new dimensionless parameter, the Fenn number, is introduced to define a transition between the spray regimes, in terms of its dependence on the characteristic Strouhal number for the ejection process. A fundamental relationship between the Fenn and Strouhal numbers is theoretically derived and confirmed experimentally in spraying liquid electrolytes of different ionic strength subjected to a varying magnitude electric field. This relationship and the basic understanding of the charged droplet generation physics have direct implications on the optimal ionization efficiency and mass spectrometric response for different types of analytes.

Integrating planting date with insecticide spraying regimes to manage insect pests of cowpea in north-eastern Nigeria

We sought to establish the most effective combination of planting dates with insecticide spraying regimes for the management of insect pests of cowpea in the savannas of northeast Nigeria. The results after 3 sprays, made once each at the bud initiation, flowering, and podding stages, did not differ significantly from those after 2 sprays, made once each at flowering and podding, in terms of reducing insect pest population and increasing grain yield. Despite the reduction in insect infestation, delaying planting beyond mid-August reduced cowpea grain yield by 12.3%, on average. The yield of the medium-maturing variety IT89KD-391 was significantly higher when planted in mid-August and sprayed twice than when planted on the earlier or later dates. The yield of the indeterminate late-maturing variety ITKD89-288 was higher when planted in early August and sprayed thrice. Early- and medium-maturing cowpea varieties should therefore be planted in mid-August and sprayed twice. Late-maturing indeterminate varieties should be planted in early August and sprayed thrice.

Effect of rainfall in the control of onion thrips, Thrips tabaci lindeman (Thysanoptera :Thripidae) in Sokoto, Nigeria

Field experiments were conducted in the dry seasons of 2001/2002 and 2002/2003 to study the major insect pests of onion using five dates of transplanting and five insecticidal spray regimes of λ-cyhalothrin in a randomised complete block design, replicated three times. Results indicate that thrips were the major insect pests of onion, which started colonizing onion plant in December, but the number was low until the third week of January and peaked in mid-March with up to 600 thrips/plant. In the course of the research, rainfall was recorded on 12 April, 2002 and 6 April, 2003 and this was observed to exert greater control of thrips than either planting date or the chemical (78%). In 2001/2002 season, there was a reduction in thrips population from 86-9 thrips/plant (89%) in zero spray in March transplant from 5-6 weeks after transplanting (WAT) before rising to 25 at 8 WAT, in February transplant the reduction was from 78-13 thrips/plant in zero spray. In 2002/2003 season only a slight increase in number of thrips/plant (12-15) was observed from 4-5 WAT in March transplant, but in February transplant not affected by rain there was increase was from 21-89. Where rainfall can be simulated, a greater control can be achieved, where thrips are washed away by the force of the rain, unlike chemical that may not reach the innermost leaves.

A full voltage-controlled nanoelectrospray system and its steady characteristic analysed by empirically equivalent circuit method

Nanoelectrospray technique, or electrohydrodynamic spraying, has been utilised in wide applications including mass spectrometry, microcolloid thrusters and micro/nano-fabrication areas. In this article, a nanoelectrospray system was developed in a pure voltage-controlled fashion with low flow rates of nL/min. Electrospray occurs by applying a voltage to overcome surface tension of the liquid without auxiliary backpressure. Pronounced increase of current with applied voltage was revealed during the pressure-free spray. In the steady spray regime a linear correlation between current and voltage was clearly identified; this can be attributed directly to the unforced electrospray where the spray properties are uniquely dictated by the voltage. This behaviour may be captured by an equivalent circuit method based upon empirical results. The equivalent circuit resistance, derived from the best-fit model, represents an electrical equivalence of the gap between the nozzle and the collector; this resistance strongly depends on both the nozzle size and the spray distance. The suitability of an electrical equivalent is further confirmed by incorporating a series resistor. No obvious difference can be distinguished electrically between a resistor and the resistance of the gap, suggesting that unforced spray can be adjusted and stabilised externally by using the series resistor method.

English

Field studies were conducted during the 2008 - 2009 cropping season to determine the minimal insecticide application which can reduce cowpea yield losses on the field due to insect pest infestations in the Transkei region of South Africa. Treatments consisted of five cowpea varieties and four regimes of insecticide spray which were laid out with a split-plot experimental design with four replications. Observations were taken on the incidence of major insect pests, cowpea pod and seed damage by insects as well as growth and yield parameters of the cowpea varieties. Results showed that spray regimes had significant effects on insect population counts, pod and seed damage and consequently on cowpea yield parameters. Application of insecticide once each at flower budding and early podding significantly reduced pod borers and pod-sucking bugs infestations by 44 and 56%, respectively, compared to the untreated control. Application of insecticide, once at flower budding, early podding and pod filling significantly reduced pod and seed damage, resulting in substantial increase in number of pods, pod weight and seed weight per plant, and also number of seeds per pod of cowpea compared to the untreated control. This study provides information on the incidence of major insect pests of cowpea as well as the minimum insecticide control intervention necessary for effectively reducing cowpea yield losses on the field. Two insecticide spray regimes (once at flowering and podding) significantly reduced insect population and damage of cowpea.

Synthetic sex pheromone attracts the leishmaniasis vector Lutzomyia longipalpis to experimental chicken sheds treated with insecticide

BackgroundCurrent strategies for controlling American visceral leishmaniasis (AVL) have been unable to prevent the spread of the disease across Brazil. With no effective vaccine and culling of infected dogs an unpopular and unsuccessful alternative, new tools are urgently needed to manage populations of the sand fly vector, Lutzomyia longipalpis Lutz and Neiva (Diptera: Psychodidae). Here, we test two potential strategies for improving L. longipalpis control using the synthetic sand fly pheromone (±)-9-methylgermacrene-B: the first in conjunction with spraying of animal houses with insecticide, the second using coloured sticky traps.ResultsAddition of synthetic pheromone resulted in greater numbers of male and female sand flies being caught and killed at experimental chicken sheds sprayed with insecticide, compared to pheromone-less controls. Furthermore, a ten-fold increase in the amount of sex pheromone released from test sheds increased the number of females attracted and subsequently killed. Treating sheds with insecticide alone resulted in a significant decrease in numbers of males attracted to sheds (compared to pre-spraying levels), and a near significant decrease in numbers of females. However, this effect was reversed through addition of synthetic pheromone at the time of insecticide spraying, leading to an increase in number of flies attracted post-treatment.In field trials of commercially available different coloured sticky traps, yellow traps caught more males than blue traps when placed in chicken sheds. In addition, yellow traps fitted with 10 pheromone lures caught significantly more males than pheromone-less controls. However, while female sand flies showed a preference for both blue and yellow pheromone traps sticky traps over white traps in the laboratory, neither colour caught significant numbers of females in chicken sheds, either with or without pheromone.ConclusionsWe conclude that synthetic pheromone could currently be most effectively deployed for sand fly control through combination with existing insecticide spraying regimes. Development of a standalone pheromone trap remains a possibility, but such devices may require an additional attractive host odour component to be fully effective.

Efficacy of some plant extracts in the management of cercospora leaf spot of groundnut in the Sudan savanna of Nigeria

Field trials were conducted to evaluate the efficacy of neem seed, garlic clove, onion bulb, ginger rhizome and pawpaw leaf extracts applied as foliar spray in controlling cercospora leaf spot of groundnut in the Sudan savanna of Nigeria during the 2002 and 2003 cropping seasons. Ridomil was used as a positive check while the control was left untreated. Three spray regimes (once, twice and thrice) were evaluated. A strip plot design with three replications was used in setting up the experiments. Ex-Dakar, a cercospora leaf spot susceptible Spanish Valencia groundnut variety, was used as planting material. All the plant extracts reduced the incidence and severity of cercospora leaf spot in both seasons compared to the untreated crops. However, neem seed and garlic clove extracts significantly reduced the incidence and severity of the disease compared to the other plant extracts. Ridomil was more effective in controlling the disease than the plant extracts. Three sprays with the plant extracts gave better control of the disease than one or two sprays in the season. The highest seed yield of 3115 kg/ha and 3311 kg/ha in 2002 and 2003, respectively, were obtained with neem seed extract treatment while the lowest seed yield of 2134 kg/ha and 2334 kg/ha in 2002 and 2003, respectively, were recorded from the untreated crops. Also the highest seed yield of 3124 kg/ha and 3418 kg/ha in 2002 and 2003, respectively were obtained following three sprays compared to 2523 kg/ha and 2641 kg/ha for one spray in 2002 and 2003, respectively and 2840 kg/ha and 3085 kg/ha for two sprays in 2002 and 2003, respectively. The highest haulm yield of 4121 kg/ha and 4089 kg/ha in 2002 and 2003, respectively were also obtained following treatment with neem seed extract. The lowest haulm yield of 2951 kg/ha and 3045 kg/ha in 2002 and 2003 respectively, were recorded from the control. Three sprays gave higher haulm yield (4265 kg/ha and 4279 kg/ha in 2002 and 2003, respectively) than one and two sprays in the season. Neem seed extract could therefore be used to control cercospora leaf spot and to improve groundnut production in the Sudan savanna of Nigeria.

Efficacy of integrating seed treatment with apron star 42WS and foliar application of emulsified neem (Azadirachta indica, a. juss) seed oil on the management of covered and long smuts of sorghum (Sorghum bicolar l. moench) in the Sudan savanna of Nigeria

Field trials were conducted in 1999 and 2000 cropping seasons to evaluate the efficacy of integrating seed treatment with fungicide (Apron Star 42WS) and foliar application of emulsified neem seed oil on the control of sorghum smuts in the Sudan savanna of Nigeria. A strip plot design with three replications was employed to test the effects of the treatments. Seed dressing with Apron Star was assigned to the main plot while foliar application of emulsified neem seed oil constituted the subplot factor. Three spray regimes of one, two and three sprays of the neem seed oil were used. The results showed that covered and long smuts were the smuts identified infecting the crop in the two seasons. Seed treatment with Apron Star supplemented with foliar sprays of neem seed oil significantly reduced the incidence and severity of the two smuts in both seasons compared to the untreated crops. Emulsified neem seed oil spray regime did not give significant variation in the incidence and severity of both smuts, however, three sprays of the neem seed oil gave lower incidence and severity of the diseases compared to one and two sprays. Grain yield was significantly higher in the treated than the untreated crops (control) (1.34 t/ha and 0.76 t/ha, respectively, for the combined two years analysis). Grain yield was also significantly higher following three applications of the neem seed oil than one spray and the untreated crops. Seed treatment with Apron Star 42WS supplemented with neem seed oil could be recommended for the management of covered and long smuts in the Sudan savanna of Nigeria.

Efficacy of fungicide mixtures for the management of Phytophthora infestans (US-1) on potato

Fungicide application strategies (timing, frequency, rates and mixtures) are important for the control and resistance management of potato late blight caused by Phytophthora infestans. The efficacy of fungicide mixtures consisting of fenamidone + mancozeb and propamocarb HCL + mancozeb at various rates and in spray regimes containing metalaxyl and mancozeb was evaluated for late blight control (US-1) at four locations in Kenya. Propamocarb HCL + mancozeb significantly (P < 0.05) reduced foliar blight compared with mancozeb and the untreated control under moderate to severe disease pressure. Disease severity was significantly lower following application of propamocarb HCL + mancozeb at a rate of 4L ha-1 than at rates of 2L and 3L ha-1 in 1999 and 2000, but it was not significantly lower following applications at a rate of 3L ha-1 in 2000 and 2001. There were no significant differences in mean final late blight score among the three rates of 0.9, 1.0 and 1.1 kg ha-1 of fenamidone + mancozeb. All fungicide mixtures and application sequences significantly reduced the area under the disease progress curve and final late blight scores as compared with the unprotected control. Total and marketable tuber yield significantly (P < 0.05) increased in all fungicide-treated plots.

Impact of insecticide-manipulated defoliation by Japanese beetle (Popillia japonica) on grapevines from vineyard establishment through production

Japanese beetle (JB), Popillia japonica Newman, is a severe pest of grapes in the southeastern USA where viticulture is a growing industry. This study evaluated the impact of foliar injury from JB field populations on growth, fruit ripening, berry composition and yield of young vines of six cultivars from vineyard establishment through the first year of production. Three spray regimes, carbaryl applied every 7 or 14 days, or no insecticide, were used to manipulate levels of defoliation by JB. Cultivars varied in susceptibility and response to defoliation by JB. Some (e.g. Norton) showed reduced vine growth and delayed post-veraison increase in total soluble sugars and pH, as well as reduced cluster number and weight, berries per cluster and yield. Others (e.g. Concord) showed little or no measurable impact from JB. Notably, the biweekly spray regime was as effective as weekly sprays in mitigating the impacts of defoliation. Foliar loss from JB feeding can set back establishment and productivity of young grapevines. Nevertheless, many growers can reduce spray frequency without compromising the benefits of JB management. Even susceptible cultivars can tolerate low to moderate (<20%) levels of defoliation, and some are resistant enough to be grown without treating for JB.

LARGE EDDY SIMULATION OF DROPLET STOKES NUMBER EFFECTS ON TURBULENT SPRAY SHAPE

The spatial and temporal development of a spray strongly depends on the local characteristics of turbulence. The turbulence-droplet coupling gives rise to droplet dispersion, which is the underlaying physical phenomenon of interest in this study. Large eddy simulations (LES) provide details of the instantaneous flow field and anisotropy of the larger scales. Hence, LES has the potential of improved spray simulations in flows that are highly nonisotropic/nonstationary. A numerical study on the effect of droplet diameter (d) on spray shape is described by carefully varying d. The droplets are assumed to be non-interacting with each other. They are also assumed to maintain their shape and diameter. The droplet Stokes numbers are within the range 0.07 <= St(p) < 2.56, corresponding to diameters 2 < d < 12 am for a common liquid fuel. In order to emulate a fuel spray, a droplet-laden jet at Re = 10,000 and Ma = 0.3 is considered as a model problem that avoids the dense spray regime. A novel technique to visualize the simulated sprays in a realistic manner is presented, and a qualitative comparison to a diesel spray experiments is made. It is shown that the spray-cloud shape depends strongly on droplet Stokes number. A spray penetration correlation formula is suggested. The nonlinear character of the droplet-eddy interaction and its dependence on droplet size is studied by visualization of droplet trajectories. We show that the spray behavior can be coherently explained by considering the statistical properties of the droplet cloud. The results show that the instantaneous/short-time-averaged probability density functions (PDFs) of droplet statistics explain very coherently the St(p) dependency of the spray shape. The PDFs of the axial and radial components of droplet-gas slip velocity (u(g) - u(p)) are used to explain the visual observations on the spray cloud evolution.

Managing Oriental Fruit Fly (Diptera: Tephritidae), With Spinosad-Based Protein Bait Sprays and Sanitation in Papaya Orchards in Hawaii

The efficacy of GF-120 NF Naturalyte Fruit Fly Bait in combination with field sanitation was assessed as a control for female oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), in papaya (Carica papaya L.) orchards in Hawaii. Three different bait spray regimes were evaluated: every row (high use of the bait), every fifth row (moderate use), and every 10th row (low use). Orchard plots in which no bait was applied served as controls. For five of the seven biweekly periods that followed the first bait spray, trapping data revealed significantly fewer female B. dorsalis captured in plots subject to high and moderate bait use than in control plots. Differences in incidence of infestation among treatments were detected only by the third (12 wk after first spray) fruit sampling with significantly fewer infested one-fourth to one-half ripe papaya fruit in plots subject to high and moderate bait use than in control plots. Parasitism rates by Fopius arisanus (Sonan) (Hymenoptera: Braconidae) were not negatively affected by bait application. Results indicate that foliar applications of GF-120 NF Naturalyte Fruit Fly Bait either to all rows (every other tree), or to every fifth row (every tree) in combination with good sanitation can effectively reduce infestation by B. dorsalis in papaya orchards in Hawaii.

Current-Controlled Nanospray Ionization Mass Spectrometry

The hypothesis that direct determination of electrospray current would provide a viable method for maintaining spray stability to enable optimal nanospray analysis was tested by building a feedback apparatus capable of reading the current and readjusting the emitter voltage in real time. The apparatus consists of a current-sensing circuit that reads the voltage drop across a resistor located between the high-voltage power supply and the nanospray emitter. A low voltage proportional to the observed current is generated and sent to a data acquisition card. The information is used by a proportional-derivative-integral (PID) algorithm to calculate the magnitude of a low-voltage signal that is used to control the power supply output. Any variation of current across the sensing resistor is thus counteracted by an opposite-direction variation of the high voltage applied to the nanospray emitter. In this way, the apparatus adjusts the emitter voltage to achieve a preset value of current, which it strives to maintain over time in spite of any possible variation of the parameters influencing the spray regime. Preliminary results have shown that the feedback apparatus is capable of establishing and maintaining stable spray for samples that are usually considered challenging in traditional voltage-controlled analysis, such as those consisting of nucleic acid solutions with high salt loads. For these types of samples, the total ion count recorded in current-controlled mode was significantly more stable than that observed in voltage-controlled mode. At the same time, overall signal intensities and signal-to-noise ratios were also significantly improved. Setting the target nanospray current to a predefined value and letting the apparatus reach the target without operator intervention enabled the acquisition of viable data from solutions containing up to 2.5 M ammonium acetate, which are ordinarily difficult by traditional manual tuning. A deeper understanding of the current-voltage relationships for samples of very different compositions is expected to enable one not only to predict the target current that should be used for a certain analysis, but also to devise algorithms to change such target as a function of predictable variations of sample properties and analytical conditions. This will allow for optimal performance to be maintained during on-line gradient chromatography in which the nature of the sprayed solution may vary very widely during the course of the analysis.

Triazole sprays induce diffuse browning disorder in ‘Cox's Orange Pippin’ apples in controlled atmosphere storage

The inclusion of triazole chemicals in orchard spray programmes was investigated as a possible cause of a physiological storage disorder (diffuse browning disorder or DBD) that has seriously affected commercial consignments of ‘Cox's Orange Pippin’ apples ( Malus domestica Borkh.) since 2000. In 2006, spray regimes that included or excluded the triazole plant growth regulator paclobutrazol and triazole fungicides myclobutanil and penconazole were compared in each of nine commercial ‘Cox’ orchards. In 2007 the number of orchards was reduced to eight but the number of treatments was increased in order to compare the effects of paclobutrazol separately from those of the triazole fungicides. Apples were stored in controlled atmosphere (CA) conditions of 1.2 kPa O 2 and <1 kPa CO 2 at 3.5 °C for 5 months and assessed for presence of DBD after a further 7 d at 20 °C. In 2007 additional samples were subjected to a delayed cooling (7 d at 20 °C) or postharvest treatment with diphenylamine (DPA) or 1-methylcyclopropene (1-MCP). In both years DBD did not develop where triazole chemicals were omitted from the spray programmes, whereas the inclusion of triazole chemicals resulted in DBD development in fruit from 67% and 71% of orchards in 2006 and 2007, respectively. Fungicide application was more conducive to DBD development than application of paclobutrazol but, in combination, induced the highest incidence of DBD. Triazole (fungicides + paclobutrazol) application generally increased the respiration rate of CA-stored fruit but ethylene production rates were not affected. The development of DBD was not affected by post harvest application of DPA or 1-MCP or a delayed cooling of the fruit.

Spray treatments combined with climate modification for the management of Leveillula taurica in sweet pepper

The effects of several spray and climate treatments on Leveillula taurica were tested under controlled and commercial greenhouse conditions either alone or combined with a climate treatment. Ampelomyces quisqualis AQ10 inhibited the germination of conidia on leaves, but not on glass. Trichoderma harzianum T39 inhibited germination on both surfaces. Neither the examined biological control agents (BCAs) nor the two tested mineral oils (AddQ and JMS Stylet-Oil) affected the viability of conidia. Sulphur drastically limited the germination and viability of L. taurica. In experiments at 15–25°C, AQ10 alone reduced hyphal leaf colonisation at 25°C. T. harzianum T39 significantly reduced leaf colonisation at all temperatures but significantly reduced disease only at 20–25°C. The oils significantly reduced leaf colonisation and sulphur reduced both leaf colonisation and disease at all temperatures. Results were confirmed in an experimental greenhouse. In a field experiment, azoxystrobin, polyoxin AL, neem extract, and T39 were effective; sulphur was superior to them. Under severe epidemic conditions the disease had a negative impact on yield; late fungicide treatments at spring-time were found unnecessary. Chemical sprays applied in alternation was compared with the ‘friendly’ spray regime (alternation of Heliosoufre, T. harzianum T39 + JMS Stylet oil, A. quisqualis AQ10+AddQ oil and Neemgard) in two climates i.e. (i.) day warm climate and (ii.) regular (cool) day climate regimes. In the warm climate, there was no significant difference in the performance of the ‘friendly’ spray regime and the chemical spray regime. However, in the cooler climate, the ‘friendly’ spray programme was not as effective as the chemical spray programme. It was concluded that a change in the greenhouse climate may affect the development of powdery mildew and, at the same time, promote the activity of BCAs and render a pathogen more vulnerable to these control agents, allowing for better disease suppression.