Deposition and biological efficacy of a fungicide applied in charged and uncharged sprays in cereal crops

Barley and wheat crops were both sprayed at growth stages 30 and 61–75 with boom-mounted conventional hydraulic nozzles (250 ?/ha), experimental hydraulic electrostatic nozzles (66 ?/ha), electrically driven spinning discs (2 ?/ha, oil-based sprays and 5 ?/ha, aqueous spray) and ‘Electrodyn’ nozzles (1 and 2 ?/ha, oil). The ULV spray systems (up to 5 ?/haS) were used with or without air assistance. The distribution of both oil and aqueous sprays within the crops was measured with fluorescent tracers on plant parts and on whole plants. An experimental triazole fungicide (mixed with tracer) was applied to the crops by all the spray systems and the degree of control of leaf blotch (scald) caused by Rhynchosporium secalis (Oudem.) J.J. Davis in barley and mildew (Erysiphe graminis DC) in wheat compared with the deposit data. The two highest-volume spray systems gave similar results for disease control and there was no significant difference between the charged and uncharged sprays at 66 ?/ha. The Micron Ulva spinning disc and ‘Electrodyn’ systems with air assistance also performed well. Unassisted ULV sprays were often unevenly distributed within the crops and gave inferior disease control. The ‘Electrodyn’ system often produced large total deposits relative to other spray systems but unassisted sprays were mainly deposited on the upper plant parts. The results indicate that application at volumes as low as 1 ?/h can be as biologically effective as conventional high-volume spraying, when compared at the same dose rate of fungicide (90 g/ha). Relationships between spray distribution within cereals and the sites for pest and disease attack are discussed with regard to different methods of application.     

Low volume spraying on cotton: a comparison between spray distribution using charged and uncharged droplets applied by two spinning disc sprayers

Two hand held spinning disc sprayers, one producing electrostatically charged spray, were assessed and compared on Egyptian cotton. The charged droplets produced greater overall deposition with a higher proportion on the undersurface of leaves. Spinning disc sprayers offer smallholder cotton farmers several advantages over higher volume sprays applied by knapsack sprayers, and it is suggested that charged rotary atomisers merit further consideration for controlling troublesome cotton pests such as whiteflies which are found on the undersurface of leaves.     

Effects of application methods,spray volumes,pressures and herbicide rates on weed control in spring cereals

Herbicides were sprayed in spring cereals with conventional and low pressure hydraulic flat-fan spray nozzles and rotary atomizers. The biological effects were measured on weeds and oats. In addition, some spray retention studies were performed. Conventional flat-fan spray nozzles at a spraying pressure of 2 or 4 bar (200 or 400 kPa) gave the best effect. There was no difference in effect between spray volumes of 125 1/ha and 250 1/ha. In most field situations, 200 kPa and 125 1/ha should be preferred. However, when the spray volume is reduced from 250 to 125 1/ha, the droplet size decreases and the drift hazard increases. Where great care has to be taken, the use of conventional flat-fan spray or low-pressure nozzles at 100 kPa and 250 1/ha may be a compromise between effect and safety.     

Assessment of electrodynamic spraying as an alternative to ultra-low-volume spraying in western Tanzania

The introduction of ULV (ultra-low-volume) spraying to cotton farmers in western Tanzania in the early 1970s was a major contribution to the cotton industry as the control of cotton insect pests was made easier and possible in many areas. However, spray drift and increased cost of ULV insecticides and batteries have been major constraints to ULV spraying in recent years, so a spraying technique allowing greater efficacy and reduced costs is needed. Trials to assess the potential of electrodynamic spraying as an alternative to ULV spraying started in western Tanzania in 1979. The present study assessed swath width, dosage rates and farmer's reaction to the ‘Electrodyn’® hand-held sprayer as compared with the hand-held spinning-disc sprayer (Micron ULVA), currently used by farmers in Tanzania, in order to identify the optimum combination package to be recommended to farmers. Cypermethrin ED applied at a dosage rate of 15·8–31·6 g a.i./ha by the Electrodyn sprayer over a swath width of 3·0 m gave good control of H. armigera. Yields of seed cotton were comparable to those with ULV cypermethrin applied at a dosage rate of 62·5 g a.i./ha. The spray volume was reduced from 2·5 l/ha applied with the spinning disc to 0·35 l/ha with electrodynamic spraying. Reduced drift, dosage of active ingredient and volume rates, and reduction in the number of batteries needed in a season, were among the major advantages of electrodynamic spraying over ULV spraying in western Tanzania.     

Cost benefits of integrating nitrogen,plant growth regulators and fungicides in winter barley

Data from experiments on winter barley sown in mid-September in south-west England between 1983 and 1985 have shown that fungicide programmes, involving up to three sprays per season, provided increased profits at a market value for barley of £100 per tonne of between £53 and £250/ha, depending on variety and nitrogen timing. On non-fungicide treated crops an overall mean benefit of between £28 and £154/ha was obtained by delaying the main nitrogen dressing from mid-March to mid-April, irrespective of site or season. Responses to a plant growth regulator application at GS 30 were more variable, but overall were more cost effective when applied to March nitrogen crops. Integration of these management variables has identified areas where increased profit can be achieved with similar or even reduced agronomic inputs. Overall, two spring-applied fungicide sprays were consistently profitable irrespective of nitrogen timing, whereas the inclusion of an autumn fungicide spray frequently decreased gross margins. In 1985, the financial impact of management variables was studied in crops that received the main nitrogen dressing either in mid-March or in mid-April. A single fungicide spray, applied when the flag leaf was fully emerged (GS 39) to cvs Igri, Sonja, Halcyon and Tipper that received the main nitrogen dressing in mid-March, increased gross margins by 41%, 21%, 10% and 35% respectively, whereas the same fungicide treatment applied to crops that received the main nitrogen dressing in mid-April further increased the gross margin to 51%, 48%, 21% and 47% respectively compared with crops that received no fungicide and the main nitrogen dressing in mid-March. The addition of an autumn fungicide spray improved gross margins for each variety when the main nitrogen dressing was applied in mid-March but not mid-April. The profitability at a reduced market value for barley of £80/t is discussed.     

Assessing the deposition and canopy penetration of nozzles with different spray qualities in an oat (Avena sativa L.) canopy

Consistent spray coverage that is evenly distributed throughout the canopy is necessary to control pest populations that can negatively affect yield. As applicators are switching to Coarser spray quality nozzles to reduce risk and liability of pesticide spray drift, concerns about efficacy loss are growing. Previous research has indicated that small droplets are the most effective at penetrating through crop canopies, but newer nozzle technologies have improved the effectiveness of larger droplet or Coarser sprays. Research was conducted to assess the canopy penetration of nozzles that produce Coarse, Very-Coarse and Extremely-Coarse spray qualities compared to nozzles that produce Fine and Medium spray qualities. Kromekote collectors were positioned in four configurations in an oat (Avena sativa L.) var. ‘Yarran’ (AusWest Seeds, Forbes, NSW, Australia) crop to quantify the coverage and droplet number densities (droplets cm⁻²) across three application carrier volume rates: 50, 75 and 100 L ha⁻¹. Applications were made in the field in 30 cm tall, tillering oats, with collectors arranged in a randomised complete block design with three replications. The entire study was repeated on the following day. Results showed that droplet number densities were inversely related to the droplet size produced by the nozzles, yet coverage was increased more by application volume rate than droplet size. Thus, both spray drift reduction and improved canopy penetration can be achieved with proper nozzle selection and operation parameters for the control of agronomic pests.     

Control of apple diseases and pests with low spray volumes and reduced chemical rates

Fungicides applied in volumes of either 100, 200 or 800 l/ha controlled apple scab in large-scale field experiments from 1982 to 1985. Either Sonax C, a formulated mixture of etaconazole and captan applied at 1 kg/ha (one-third the recommended rate), or fenarimol at 112 ml/ha (one-quarter the recommended rate), controlled scab when applied in 100 or 200 l/ha respectively. Scab was controlled with either eight protectant or at least five eradicant applications of Sonax C at either 3 or 1 kg/ha in 200 1 of water per hectare. In all years, weather conditions favoured the development of scab. In unsprayed trees the incidence of scabbed fruit ranged from 60% in cv. Granny Smith to 26% in cv. Jonathan. In sprayed trees fruit infection rarely exceeded 1%. The control of powdery mildew was unsatisfactory with Sonax C applied at 1 kg in 100 l/ha. Better control was achieved by either increasing the spray volume or the rate of fungicide per hectare. Two-spotted and European mites were controlled with propargite at the recommended rate of 5·5 kg/ha at either 200 or 800 l/ha. Codling moth was controlled with 160 ml/ha of azinphos-methyl (one-quarter the recommended rate) applied in 800 l/ha.     

Effects of charging voltage,application speed,target height,and orientation upon charged spray deposition on leaf abaxial and adaxial surfaces

Wastage of agricultural chemicals and ensuing environmental pollution is an issue, where ineffective spray deposition is a major concern with conventional pesticide application methods. Electrostatic spraying is known to be one of the most effective methods to improve leaf abaxial (underside) surface deposition, overall deposition, and distribution on the plant targets. Deposition of charged sprays on leaf abaxial and adaxial (upper) surfaces as influenced by the spray charging voltage (system), application speed (operational), target height and orientation (target) parameters was studied in the laboratory. An air-assisted electrostatic induction spray charging system attached to a moving carriage was used to apply charged spray at uniform application (ground) speeds. Spray deposition (101–71 μm NMD), determined using a fluorescent tracer technique increased with charging (0–5.5 mC kg⁻¹) on leaf abaxial and decreased with charging on adaxial surface. The deposition was higher on abaxial (0.66–1.33 μg cm⁻²) at 30° below (horizontal plane) and on adaxial (0.78–1.79 μg cm⁻²) at 0° (horizontal) target orientation for lower (0.278 m s⁻¹) application speed. At all target heights, abaxial deposition increased with charging voltage (0–4.0 kV) for medium application speed (0.417 m s⁻¹) and adaxial deposition decreased with charging voltage for lower application speed (0.278 m s⁻¹). The medium application speed with higher charging voltage was optimum for abaxial and adaxial deposition. The droplet velocity and charging voltage were the key factors for obtaining desired spray deposition on targets. All the selected factors including target orientation (O), application speed (S), target surface (L), and charging voltage (V), and their interactions except between O and S were significant at lower (0.35 m) and medium (0.65 m) target heights. All the factors and their interactions except between O and V were significant at higher (0.95 m) height. Electrostatically charged spray improved the underside (abaxial) and overall deposition. The deposition was substantially influenced by factors such as charging voltage, application speed, plant target height, and target orientation.     

Deposition characteristics and biological effectiveness of fungicides applied to winter wheat and the hazards of drift when using different types of hydraulic nozzles

Hydraulic-fan cone, low-pressure fan and two-chamber cone nozzles were used at 1.5, 3.0 and 6.0 bar (150, 300 and 600 kPa) to deliver 140, 200 and 3001 ha⁻¹ respectively of a fungicide spray to control mildew and yellow rust in winter wheat. No significant differences in biological effect were obtained although fan nozzles deposited significantly more on the upper parts of the stems, and two-chamber cone nozzles deposited less on the flag leaf and on the upper part of the stems. Because of their higher deposit and more even distribution, fan nozzles should be preferred, operated at a pressure of 1.5–3 bar to deliver a spray volume of 140–190 lha⁻¹ at 7 km h⁻¹ and to obtain an acceptable biological effect. Higher pressure (6 bar) and volume rates gave no improvement in fungicide performance. Adding a surfactant or penetration oil did not change the volume median diameter or proportion of spray liquid in droplets < 150 μm. Less drift was found when using two-chamber cone nozzles at 3 bar than with flat-fan spray nozzles at 1.5 bar. It is concluded that the two-chamber cone nozzle is useful for fungicide application when drift must be avoided.     

Spray volume and fungicide rates for citrus black spot control based on tree canopy volume

The control of citrus black spot (CBS) caused by Phyllosticta citricarpa relies mainly on fungicide sprays. Generally, high and non-standardized spray volumes are adopted and the sprays are based on litre per tree or per hectare. However, the tree canopy volume may vary with age, density and variety, and this is expected to impact on the spray volume and fungicide rates needed for disease control. This study evaluated the efficacy of different fungicide spray volumes and rates for CBS control based on the tree-row-volume (TRV) concept. Two field trials were carried out during three seasons in São Paulo state, Brazil. Trials were set up in commercial orchards of late-maturing ‘Valencia’ sweet orange grown for juice production. In field trial 1, the volumes tested were 125 (standard), 100 (internal runoff point), 75 (intermediate) and 50 (half the internal runoff point) mL of spray mixture/m³ of the tree canopy. In field trial 2, 100 and 50 mL/m³ were evaluated. The fungicide rates ranged from 40 to 110 mg of metallic copper/m³ and from 1.9 to 4.7 mg of pyraclostrobin/m³. Untreated control trees (UTC) were kept unsprayed. CBS incidence and severity, premature fruit drop, yield, fungicide deposition and spray coverage were evaluated. All spray volumes tested reduced CBS incidence and severity on fruit at 75–95% and resulted in 1.6–3.0-fold higher yields than the UTC. However, a slight trend of more CBS symptoms and fruit drop, and lower yield was observed for trees treated with 50 mL/m³ compared to those treated with higher volumes. Spray volume change, from 125 to 75 mL/m³, irrespective of fungicide rate correction, led to a 40% reduction of CBS spray costs and water usage and increased the financial return of the control by up to 35%. TRV-based sprays may contribute to sustainable citrus production by reducing costs and environment impacts while maintaining efficient CBS control.     

An effect of rust (Uromyces viciae-fabae) on the yield of spring-sown field beans (Vicia faba) in the UK

Rust (Uromyces viciae-fabae) has recently been noted with increased frequency and earliness on spring-sown beans (Vicia faba) at Rothamsted. In 1982 an experiment was made to assess the damage and yield loss, if any, being caused by the disease. Plots received benomyl sprays to control chocolate spot (Botrytis fabae) or not, maneb plus mancozeb (protective) or propiconazole (systemic) fungicide applied twice or three times to control rust, or no fungicide at all. Rust was first found on 7 July and sprays were applied from 9 July but by 19 August plants of all treatments were dead. Fungicides controlled disease development during July and at harvest overall yields were 4·51 and 5·43 t/ha in unsprayed and sprayed treatments respectively. The difference was accounted for by the weight of individual grains and not by the number of pods per plant or grains per pod. Previously rust has been considered unimportant in the UK but its potential for damage is considerable.     

Control of late blight (Phytophthora infestans (Mont.) de Bary) with fungicide applied by hydraulic and electrostatic sprayers

Summary Similar amounts of metalaxyl were deposited onto potato leaves on the middle and lower parts of the stem by different tractor-mounted sprayers, but much more was deposited onto apical leaves by an electrostatic sprayer. Late blight spread into plots from inoculated guard plants but was controlled by Fubol (metalaxyl+mancozeb) at least as well when applied electrostatically (4.4 or 91/ha) as hydraulically (200l/ha).     

Rotary atomiser design requirements for optimum pesticide application efficiency

Pesticide application efficiency from aircraft could be increased substantially, and required downwind buffer distances to avoid drift damage reduced significantly, if sharp issuing points or pins were added to existing rotary cage atomizer designs. This would enable existing rotary cage units, already successfully deployed for Ultra Low Volume (ULV) applications of insecticides, to be also used for Large Droplet Placement (LDP) application of herbicides. Studies at Cranfield University using high speed photography and laser droplet sizing instrumentation demonstrated that the addition of fine pins to the final atomizing surface of the rotating cage would increase uniformity of droplet production, by promoting fluid atomization in the ligament mode. This would lead to a substantially increased percentage of droplets in the spray falling between 100 μm and 300 μm in size, suggested here as a biological/environmental droplet size optimum. Development of a ‘spinning pins’ rotary atomizer for aircraft would therefore be highly desirable for agricultural and other purposes. Investment in this technology has the potential to significantly reduce pollution of atmosphere, soil, fresh water and oceans with pesticides.     

Improving spring and summer fungicide treatments for winter barley

The response of winter barley to broad-spectrum fungicides applied at first node stage [growth stage (GS) 31] or as two-spray programmes [first node stage and flag leaf to ear emergence (GS 39–59)] was examined at 22 sites over five years during 1986–1990. Single sprays were also applied at an intermediate timing [third node to flag leaf emerging (GS 33–37)] at all sites in 1989 and 1990. The mean response to the single spray at GS 30–31 was 0.86 t ha⁻¹ but ranged from 0.25 to 3.03 t ha⁻¹ (4–80%). With the addition of a late spray (GS 39–59) of propiconazole plus tridemorph to the spring treatment, mean response was 1.25 t ha⁻¹ [range 0.35–3.32 t ha⁻¹ (5–87%)]. There were some differences between fungicides and fungicide mixtures applied at GS 31 and a prochloraz component was needed for effective control of eyespot. Seasonal differences in the mean response to the GS 39–59 treatment reflected differences in disease pressure after GS 59. The GS 30–31 treatment failed to maintain disease control up to the milky ripe stage (GS 75) in years when disease pressure was high. Yield responses were correlated with disease severity on leaf 2 at the time of the spring (GS 31) application and with the degree of control of eyespot on the stem base and of foliar diseases on the flag leaf at GS 75. A single spray applied at GS 33–37 gave comparable yields to the two-spray programmes and has potential to improve profitability where disease levels are low at the first node stage.     

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.     

Comparative droplet-size spectra for three different-angled flat fan nozzles

Droplet-size spectra for 110-, 80- and 65-degree flat fan nozzles of equal output were measured at distances 5–45 cm from the nozzle using a laser diffraction system. The volume median diameters (VMDs) decreased between 5 and 20 cm from the nozzle and increased with distance at distances greater than 30 cm. Similarly, the proportion of small droplets in the spray was greatest at about 20 cm with subsequent reduction with distance. The VMDs at each distance decreased with increasing nozzle angle and the corresponding percentage of small droplets increased. Addition of wetting agent had little effect up to 0·01% v/v. Increasing concentrations lowered the VMD and raised the percentage of small droplets.     

Evaluation of a forecaster for downy mildew of onion (Allium cepa L.)

A forecaster of onion downy mildew, referred to as DOWNCAST, was evaluated under field conditions to determine its validity and effectiveness for timing fungicide sprays. DOWNCAST utilized criteria for predicting sporulation and infection by the downy mildew pathogen, Peronospora destructor. The criteria were based on quantitative and temporal relationships of temperature, rain, high humidity, rate of dew deposition and dew duration with the infection cycle of the pathogen. DOWNCAST correctly predicted sporulation incidence on 111 of 119 nights during two growing seasons. Refinement of a temperature criterion was needed to predict sporulation correctly on the remaining eight nights. Indirect evidence showed that DOWNCAST correctly predicted infection incidence. Sequences of weather conditions were used to predict ‘sporulation-infection periods’, when the pathogen sporulated, survived and infected the onions, and to identify infection cycles. Fungicide programmes of Ridomil-MZ, Sandofan M8, Bravosan, Vinicur M-SC, Manzate 200 or Bravo 500, begun on the sixth or eighth day of the first infection cycle, did not usually reduce sporulation incidence early in the second infection cycle. However, all of the programmes except Bravosan and Bravo effectively restored disease management a few days later. Programmes of Ridomil-MZ begun in the second infection cycle usually were less effective than those begun in the first cycle. Relative effectiveness of the various fungicide programmes was reflected in increased yield and size of the onions. It was concluded that fungicide programmes should start at about the time of the first sporulation-infection period.     

Sprayer type and water volume influence pesticide deposition and control of insect pests and diseases in juice grapes

In a mature Vitis labrusca L. “Niagara” vineyard, we compared an airblast sprayer and an air-assisted rotary atomizer (AARA) low-volume sprayer for coverage of grape clusters and control of grape berry moth, Paralobesia viteana. In addition, the effect of spray volume on control of fungal diseases was evaluated using the fungicides ziram and azoxystrobin applied with an airblast sprayer. For evaluation of coverage, sprayers applied kaolin clay at 28 kg/ha to grapevines while operating at low, medium and high water volumes. Kaolin residues on grape clusters were analyzed to compare the total amount of spray material deposited, percent of fruit surface covered, number of deposits, size of deposits and distance between deposits. There were no significant differences between sprayers or water volumes in the total amount of kaolin deposited on clusters, but the percent surface coverage was much greater on outside-facing berry surfaces (facing the sprayer) than inside-facing surfaces (facing the rachis). On the outside-facing berry surfaces, the airblast sprayer at 468 L/ha of water (medium volume) provided the highest percent coverage, the greatest density of deposits, the largest deposit diameter, and the smallest distance between deposits. On the inside-facing berry surfaces, the same sprayer–volume combination provided the highest percent coverage and greatest deposit diameter, but deposits from the airblast sprayer operating at 935 L/ha (high volume) had the smallest distance between deposits. No significant differences between sprayers or among water volumes were detected in the deposit density on the inside-facing berry surfaces. Bioassays of grape clusters sprayed with fenpropathrin or methoxyfenozide using the airblast or AARA sprayers at two water volumes revealed the greatest fruit protection from P. viteana at the higher volume for the airblast sprayer, but at the lower volume for the AARA sprayer. Spray volume of the airblast sprayer also affected disease control by the protectant fungicide ziram more than by the systemic fungicide azoxystrobin, with 468 L/ha providing better control than 187 L/ha. However, for most diseases, fungicide type was more influential than spray volume in determining the disease control outcome. The results of this study emphasize the need for appropriate water volumes relative to the sprayer and pesticide being used to optimize pest and disease control in juice grape vineyards.     

Fungicide treatments affect yield and moisture content of grain and straw in winter wheat

Straw and grain yield and water content in both grain and straw were measured during 3 years in 17 varieties of winter wheat following treatments with different fungicides. The water content of the straw varied significantly dependent on year, variety and fungicide treatment. In 1998, the water content in straw was significantly higher after the use of strobilurins compared with untreated and EBI fungicides (ergosterol biosyntesis inhibitors). On average water content in 10 varieties increased from 15% in untreated to 31% after applying two full dosages of azoxystrobin. In 1999 and 2000, lower dosages of azoxystrobin were used and water content increased only by 2–4 percentage units. The results indicate that in some years and with high doses precaution has to be taken following the use of strobilurins regarding handling and removing of the straw, which likely will include postponement of baling. Water content in grain was also increased significantly from fungicide treatments, but the increase was minor and at the maximum increase found to be 1.1% percentage unit. The effect of fungicide input on water content in grain was reduced much faster during the ripening period than for water content in straw. Fungicide treatments and varieties significantly influenced straw yields. The yield increases in straw varied between 0 and 1.0 tonnes/ha depending on year and variety, and was on average 0.42 tonnes/ha for two fungicide treatments. Two fungicide applications carried out at GS 31 and 45–55 gave only slightly higher increases compared with one application around ear emergence. Varieties showed variable increases following the use of fungicides. The variation was not influenced by the straw length (crop height). The increases in straw yield from fungicide treatments were relatively low compared to the increases in grain yield and no clear correlation was found between grain yield increases and straw yield increases.     

Activities of azoxystrobin and difenoconazole against Alternaria alternata and their control efficacy

Tobacco brown spot caused by Alteraria alternata is a devastating disease of tobacco worldwide. In this study, we reported the effects of a strobilurin fungicide azoxystrobin and a sterol inhibitor difenoconazole on mycelial growth, spore germination, and control of brown spot. Both mycelial growth and spore germination bioassay results showed that sensitivity of A. alternata to difenoconazole was significantly lower than that to azoxystrobin. Azoxystrobin and the compound of azoxystrobin plus difenoconazole provided excellent control efficacy on tobacco brown spot in field. Disease control efficacies for three sprays of azoxystrobin at doses of 0.094, 0.19 and 0.28 Kg a.i./ha, of azoxystrobin plus difenoconazole at 0.15, 0.22 and 0.29 Kg a.i./ha, and of difenoconazole at 0.12 Kg a.i./ha were between 86.00% and 89.67%, between 86.14% and 89.23%, and between 55.14 and 58.41%, respectively. No phytotoxic symptoms were observed for the fungicides in field. These fungicides could potentially be used for brown spot control in tobacco.