|
Pesticides Research No. 116 2008 of fungicide application in winter wheat 2 Materials and methods
2.1 Field experimentsField experiments were carried out in winter wheat at four sites in Denmark with high spatial variation in soil and terrain; two sites in each of the years 2005 (Schackenborg and Nissumgaard) and 2006 (Nissumgaard and Dybvad). The site at Schackenborg is located close to the village Møgeltønder and west of the town Tønder in southern Jutland on a sandy soil overlaying clayey deposits from the marshes. The site at Nissumgård is located close to the village Gjesing between Skanderborg and Odder in eastern Jutland on moraine deposits varying in soil type from sandy to sandy loam. The site at Dybvad is also located in eastern Jutland on moraine deposits varying in soil type from loamy sand to sandy loam. All locations were chosen to be relatively inhomogeneous fields with respect to soil type, and at Nissumgård and Dybvad also with variable topography, in order to favour different responses to nitrogen and fungicide treatments. Each experiment was conducted in a two-factorial design with fungicide dose and N strategy (Table 1). The fungicide treatments consisted of increasing doses of Opus (125 g L-1 epoxiconazol) applied at GS 39. The N strategies consisted of three different rates of mineral fertiliser N applied in a split treatment and a normal rate of N applied in a single treatment. In all split treatments 50 kg N ha-1 was applied in early April. The remaining N and the full rate of the single N treatment were applied at stem elongation (late April). Table 1. Factors and treatments in the experiment.
The experimental factors were laid out in a randomised split-plot design with N-strategy as whole-plot factor and fungicide dose as sub-plot factor. These blocks were repeated 10 times across the field in an attempt to cover most of the soil variation between replicate blocks, giving a total of 160 plots in each experiment. Net plot sizes were 27.6 m² at Nissumgård and 30 m² at Schackenborg in 2005, and 16 m² at Nissumgård and 17.7 m² at Dybvad in 2006. The crop management details are outlined in Table 2. The previous crop was winter wheat at both sites in 2005 and winter oilseed rape at both sites in 2006. The wheat was sown in mid September in both years. The site at Nissumgård in 2005 was sprayed with manganesesulphate in April. However, despite of this, manganese deficiency could be observed in some of the plots in May. There were three plots at Schackenborg in 2005 with errors in N fertiliser application. In about a third of plots 2108 and 2208 too little fertiliser had been applied, and plot 2811 had received too much fertiliser. Table 2. Crop management at the two experimental sites in 2005 and 2006.
The fungicide treatments including the tracer treatment were applied using an experimental plot sprayer equipped with a 2.5 m wide boom. The spray boom was equipped with conventional hydraulic flat fan nozzles with a mutual distance of 50 cm. The nozzle used was a Hardi S 4110-14 flat fan nozzle delivering 0.7 l min-1 corresponding to 230 l ha-1 at a driving speed of 3.6 km h-1. There was a spraying error at Dybvad in 2006, where plot 4312 did not get any fungicide application. 2.2 Measurements of soil and topographyMeasurements of soil texture, water content, topography etc. were made with three sensors:
Both mobile instruments (MobilTDR and EM38) were equipped with GPS (global positioning satellite) receivers for geo-referencing measurements. The mobile measurements related especially to soil texture were included in order to map differences in growth conditions for the individual plots. The mobile measurements were made outside the research plots in order to avoid disturbing the wheat crop. Consequently interpolation is needed in order to extend measurements inside the plots. Additionally samples of the topsoil (0-20 cm) were taken across each of the fields for comparison with the sensor measurements. Ten samples were taken at each site and analysed for soil texture. 2.3 Yield measurementsThe plots were harvested using a plot combiner. Crude grain yield was determined immediately after combining by weighing the amount of grain harvested in each plot. Samples were taken for subsequent analyses. The first step of the analysis was separation of grain and impurities, resulting in an estimate of percentage of impurities. The pure grain samples were analysed for content of water, crude protein and starch and for specific weight (100 litre weight) using NIT (Buchmann et al., 2001). Based on content of impurities and water the grain yields were transformed to dry matter grain yields, which were used in subsequent analyses. Only yield was analysed further. Due to errors at harvest, two plots at Nissumgård and one plot at Schackenborg were lost in 2005, and consequently any yield related value for these plots was set to missing in the subsequent analyses. At Nissumgård yields from 21 plots in 2006 were discarded due to errors in marking the location of the field plots. There were 6 missing yield observations at Dybvad in 2006. This number of missing data should be compared to the total of 160 plots at each site. 2.4 Disease assessmentsDisease assessments were carried out 4 times in the trials with focus on Septoria tritici (septoria leaf blotch) and Blumeria graminis (powdery mildew). Cultivars susceptible to Septoria tritici were chosen to increase the possibilities of investigating the impact on this disease.
Apart from plant pathogenic spots, physiological spots developed significantly in the cultivar Grommit grown at Schackenborg in 2005. These spots are cultivar specific as well as being influenced by various stress factors in the crop. The physiological spots complicated the assessment of septoria leaf blotch at GS 39 and 65 as the different symptoms can be difficult to separate. In 2006 only Sepotoria blotch developed significantly in the trials. In the report Septoria leaf blotch will generally just be called Septoria. 2.5 Sensor measurements of plantsMeasurements of canopy structure (leaf area index (LAI), leaf mean tip angle (MTA) and height) and N-status were all made during two major campaigns (growth stages BBCH_32 and BBCH_39) using four instruments:
Due to errors in delineation of some of the plots at Nissumgård in 2006, measurements of ViScan and MobilLas were not performed in 22 plots on any of the measurement dates in 2006. Due to data storage problems measurements of crop canopy reflectance using ViScan from 31 May 2006 at Nissumgård were only available from 11 plots. The missing ViScan data were substituted by similar data measured using MobilLas. 2.6 Fungicide deposition on leaves and soilDeposition of spray liquid was measured on the crop and at the soil surface. A tracer, brillantsulfoflavin, was used to quantify the amount of spray liquid and hence fungicide deposited on the crop and at soil level. Brillantsulfoflavin is a stable product at 5 °C and storage for several months did not cause loss of activity (Jensen and Spliid, 2003). The tracer at a concentration of 100 g ha-1 brillantsulfoflavin was added to the spray solution in treatments with the lowest fungicide dose. This means that deposition was measured in the combinations N strategy ´ replicates giving a total of 40 plots per location. Before application of tracer and fungicide mixture in the field experiment, fluorescence interactions between fungicide and tracer was tested without revealing any problems. Shortly before the experimental applications were carried out, objects were placed at soil level in order to collect the spray used for quantification of soil deposits. Rectangular filter paper objects with a size of 1.8 ´ 12 cm were used. This size allows a representative sampling, as the objects could reach from the middle of one plant row to the middle of the next row. The paper objects were placed on metal rods in order to avoid contamination with soil and in order to achieve a horizontal placement. Eight paper objects were placed in each plot. After the fungicide treatment was carried out, the paper objects were collected with two samples each consisting of four paper objects per plot. The filter papers were stored in 100 ml amber glass bottles under dark conditions at 5 oC until the samples were analysed. The tracer was solved in 50 ml demineralised water and the bottles were shaken thoroughly and a small proportion of the liquid was used for the analysis. Samples of the spray liquid were taken and stored the same way. After the fungicide treatment, 9 crop plants from each plot was taken and divided into three sections: 1) 1st leaf (flag leaf), 2) 2nd leaf and 3) 3rd leaf. These plant samples were collected in plastic bags and after transportation stored at 5 °C. The tracer was solved using 100 ml demineralised water and the samples were shaken gently in order to avoid fluorescent material from the leaves. The liquid with tracer and fungicide was collected and stored dark at 5 °C until the analysis of tracer. The leaf area of each section was determined using a Licor Area Meter (model 3100). Following this the dry weight of the leaf sections were determined by drying at 80 °C for 24 hours. The concentration of tracer in the liquid samples was determined using a Perkin Elmer model LS50B luminescence spectrometer. The bottles were shaken and a sample of 6 ml was used in the fluorescence detector. The sample was excited at a wavelength of 420 nm and after excitation emission was measured at 518 nm. The content of the sample was quantified using a number of standard concentrations ranging from 10 to 2000 mg l-1. From the concentration of brillantsulfoflavin in the sample the actual amount of tracer on the paper objects and on the leaf sections were calculated. For control purposes tracer concentration was also determined in the remaining spray solution from the experimental sprayer. Paper objects and leaf samples from untreated control were also washed with demineralised water and tested. 2.7 Overview of measurement datesThe measurements of crop characteristics were coordinated, so that the different measurement could be compared. However, due to weather conditions and time required for taking measurements, not all measurements could be performed on the intended dates (Table 3). Table 3. Overview of dates of crop measurements.
2.8 Experiment with fungicide deposition at different driving speedIn 2006 a supplementary experiment examining the influence of speed of the sprayer on deposition on leaves and soil was carried out. The experiment was carried out in winter wheat crop at Research Centre Flakkebjerg. The variety was Robigus and a two-factorial field experiment was conducted with the following factors: Factor 1. Driving speed and application technique: 1. 4 km h-1, Low drift LD-02 nozzle at 240 L ha-1 2. 8 km h-1, Low drift LD-02 nozzle at 120 L ha-1 Factor 2. Nitrogen application rate: 1. 80 kg N ha-1 2. 160 kg N ha-1 Nitrogen was applied as a single application on 18 April at both N rates. A randomised block design with 4 replicates and a plot size of 2.5 ´ 10 m was used. At 4 km/h the spray liquid consisted of tap water with addition of the tracer Rhodamin B (100 g ha-1) and a non-ionic surfactant at a concentration of 0.1%. Another tracer, Brillantsulfoflavin (100 g ha-1) was used at 8 km/h and a non-ionic surfactant was again used at a concentration of 0.1%. The surfactant used was a linear alcohol polyethoxylate (Lissapol Bio, Syngenta). The purpose of the surfactant was to give the spray liquid properties that are comparable to a spray liquid with a fungicide. The experimental treatment was carried out at growth stage BBCH 53 when the winter wheat was 75 cm high. Deposition of spray liquid was measured on 1) 1st leaf (flag leaf), 2) 2nd leaf and 3) 3rd leaf and at soil level using the same methodology as described in section 2.6. The concentration of Rhodamin B was also measured on the Perkin Elmer luminescence spectrometer. Rhodamin B was chosen as this tracer was found to interact limited with brillantsulfoflavin and has its fluorescence peak at another wavelength. Measuring Rhodamin B concentration, the sample was excited at a wavelength of 553 nm and after excitation emission was measured at 578 nm. 2.9 Statistical analysesThe plot level data were analysed using the ANOVA, GLM and MIXED procedures in the SAS system (SAS, 1996). In the general linear model, the interaction term block ´ nitrogen was used in the denominator of the F-test corresponding to the factor nitrogen, while the residual error was used for F-tests for differences between fungicide treatments and the interaction term nitrogen ´ fungicide. In the mixed models, the whole plot term (block ´ nitrogen) and blocks were having random effects, and the other factors had fixed effects. Satterthwaites method was used for calculating denominator degrees of freedom in the mixed models. Correlation and regression analyses on the sensor measurements were performed using the CORR and REG procedures of the SAS system (SAS, 1996). Regression models were compared in terms of the multiple correlation coefficient (R²) and the root means squared error (RMSE) of the model residuals.
|