The effect of spray quality on ascochyta blight control in chickpea

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Crop Protection 27 (2008) 700–709 www.elsevier.com/locate/cropro

The effect of spray quality on ascochyta blight control in chickpea C. Armstrong-Choa, G. Chongob, T. Wolfc, T. Hoggd, E. Johnsone, S. Bannizaa, a

Crop Development Centre, University of Saskatchewan, 51 Campus Drive, Saskatoon SK, Canada S7N 5A8 b Bayer CropScience , Site 600, Box 117, R.R. #6, Saskatoon, Canada SK S7 K 3J9 c Agriculture and Agri-Food Canada, Saskatoon Research Centre, 107 Science Place, Saskatoon SK, Canada S7N 0X2 d Canada-Saskatchewan Irrigation Diversification Centre, Prairie Farm Rehabilitation Administration, Agriculture and Agri-Food Canada, Outlook SK, Canada S0L 2N0 e Agriculture and Agri-Food Canada, Saskatoon Research Centre, Scott Research Farm, P.O. Box 10, Scott SK, Canada S0K 4A0 Received 17 May 2007; received in revised form 8 October 2007; accepted 9 October 2007

Abstract Ascochyta blight can completely destroy chickpea crops when weather conditions favour disease development. In addition to improving host resistance, cultural control, and fungicide application timing, the use of appropriate application technology could also enhance disease management. Differences in spray quality can influence the amount of fungicide coverage on crop plants, which could impact fungicide efficacy. The effect of application method on disease control was investigated in field trials using three nozzle types sprayed onto chickpea cultivars Myles (fern leaf) and Sanford (unifoliate). The same three nozzle types were also used in the laboratory to compare spray deposition patterns and penetration of spray into simulated crop canopies. In the field study, nozzle type had no effect on disease development or yield in any of the site years. In the laboratory study, nozzle types had no effect on the amount of spray coverage or the degree of spray penetration into the chickpea canopy. r 2007 Elsevier Ltd. All rights reserved. Keywords: Nozzle; Fungicide; Cicer arietinum; Ascochyta rabiei; Droplet size spectra; Didymella rabiei; Disease management

1. Introduction Chickpeas provide western Canadian producers with a valuable rotational alternative away from traditional cereal and oilseed-based systems, with potentially higher returns. However, heavy crop losses due to ascochyta blight caused by the fungal pathogen Ascochyta rabiei (Pass.) Labrousse have contributed to the decline in chickpea production in western Canada. Although genetic resistance is available in some cultivars, it is only partial and starts to break down at flowering (Nene and Reddy, 1987; Chongo and Gossen, 2001). As a consequence, effective fungicide application strategies are required to protect chickpea crops from the disease. Fungicide efficacy is influenced by the effectiveness of the active ingredient and the degree of coverage of the target plant. Good plant coverage depends upon many Corresponding author. Tel.: +1 306 966 2619; fax: +1 306 966 5015.

E-mail address: [email protected] (S. Banniza). 0261-2194/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2007.10.006

factors, most importantly the architecture of the plant and its leaf surface characteristics, the physico-chemical characteristics of the spray mixture, the water volume, the spray quality, and the spray trajectory. Nozzle technology has an impact on many of these variables and can therefore affect spray coverage and disease control. It has been suggested that a narrow droplet size distribution that eliminates small, easily drifting and large, poorly retained droplets can increase the efficacy of pesticide applications (Hartley and Graham-Bryce, 1980). For herbicide applications it was found that, in general, application of smaller droplets resulted in a higher efficacy compared to larger droplets (Knoche, 1994). Similarly, higher fungicide depositions on lower winter wheat leaves were observed when sprayed with an air induction nozzle compared to conventional flat fan nozzles (Marshall et al., 2000). Nozzle choice had no significant effect on sclerotinia incidence or seed yield when fungicides were applied to canola at flowering (Kutcher and Wolf, 2006). Angling spray nozzles resulted in better fungicide coverage of the middle and lower

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leaves of potato compared to straight nozzles, and angling compensated for larger droplet size (Robinson et al., 2000). It has been suggested that spray nozzle performance is influenced by carrier volume, with droplet size effects being most pronounced at low volumes (Knoche, 1994). Additional studies on chickpea grown under high disease pressure in western Canada showed that carrier volumes of 200 and 300 l ha1 applied with a conventional flat fan nozzle resulted in lower ascochyta blight severity than a carrier volume of 100 l ha1 (Armstrong-Cho, unpublished data). The objectives of the current study were to investigate the effect of different nozzle types on fungicide efficacy, and on spray deposition and penetration using the recommended carrier volume of 200 l ha1. 2. Materials and methods 2.1. Field study Field experiments were conducted in Saskatchewan, Canada from 2001 to 2003 to examine the influence of nozzle type on the efficacy of different fungicides for management of ascochyta blight in chickpea. A conventional flat fan nozzle was compared with a twin nozzle and an air-induced nozzle, representing three different spray qualities. The flat fan nozzle was a TeeJet XR8002 (Spraying Systems, Wheaton, Illinois, USA) (referred to as ‘Standard’). The twin nozzle was comprised of two XR8001 tips fitted in a Lurmark Twin Cap (Hypro Spray Group, New Brighton, Minnesota, USA) delivering two sprays, one directed 301 forward, the other 301 backward (referred to as ‘Twin’). The air-induced nozzle was an Air Bubble Jet 11002 (Billericay Farm Services Ltd., Downham, Essex, UK) (referred to as ‘Venturi’). Spray quality information for these sprays was collected using an Aerometrics PDPA 100 1-D using tap water. The spray fan was traversed through the instrument’s probe volume 1.25 cm on either side of the central X-axis, replicated three times, and compared to ASABE reference nozzles similarly tested in accordance with ASABE Standard S-572 (Table 1) (ASABE, 2004). Fungicides were applied using a carrier volume of 200 l ha1 applied at 275 kPa. Nozzles were calibrated separately at each trial location by collecting tap water for 30 s from each nozzle operating at 275 kPa. Pressures were adjusted slightly (710%) to maintain equivalent flow rates

Table 1 Spray quality parameters for the nozzles used in field and laboratory trials Nozzle

DV0.1 (mm) DV0.5 (mm) DV0.9 (mm) ASABE spray quality

XR8001 91 XR8002 93 ABJ 11002 174

152 188 348

242 324 613

Fine Fine Coarse

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from all nozzles so that the same travel speeds could be used for all treatments. Travel speed (approximately 4.6 km h1) was calculated from the calibration data. Boom height was 50 cm above the crop canopy. Depending on location, plot sizes ranged from 12 to 30 m2, with row spacing from 17 to 20 cm and a target plant density of 45 plants m2. Two chickpea cultivars, Myles (desi type) and Sanford (kabuli type), were selected for this study to investigate potential interactions between nozzle type and canopy structure created by different leaf types. Myles has intermediate resistance to ascochyta blight and fern-type leaves consisting of 9–15 leaflets, and the susceptible cultivar Sanford has unifoliate leaves. Fungicide treatments consisted of two applications; the first was made when the first disease symptoms were noted (prior to flowering), and the second application followed 10–14 d later (at early-to mid-flowering). Development of disease was encouraged by spreading infected plant material in the plots. At the Outlook site, chickpeas were grown under an overhead pivot irrigation system that was used to promote infection at this site in case of drought. All plots at this site received 50/50/25 mm in May/June/July of 2001, 50/50/ 150 mm in May/June/July of 2002 and 15 mm only in June of 2003. Disease severity ratings were performed at each fungicide spray date, followed by up to three additional ratings at regular intervals using the 0–11 Horsfall–Barratt scale (Horsfall and Barratt, 1945). Plant density and seed yield were also recorded. Thousand seed weight (TSW) and seed infection rates were based on samples of 100 and 40 seeds from each plot, respectively. Sufficient seed samples to determine TSW were not available for both cultivars in 2001 and 2002 at Saskatoon because drought or severe disease development led to premature plant death. Seed infection was not determined in 2001 and was minimal in 2003; thus results are not presented. In 2001 the field trial was conducted at Saskatoon, Outlook and Scott in central Saskatchewan. Treatments included two applications of chlorothalonil at 1000 g a.i. ha1 (Bravo 500, Syngenta Crop Protection Canada, Inc., Guelph, Ontario, Canada), azoxystrobin at 125 g a.i. ha1 (Quadris, Syngenta Crop Protection Canada, Inc.), pyraclostrobin at 100 g a.i. ha1 (Headline, BASF Canada Inc., Mississauga, Ontario, Canada), tebuconazole at 187.5 g a.i. ha1 plus 0.125% v/v non-ionic surfactant (Folicur, Bayer CropScience Inc., Calgary, Alberta, Canada) and an untreated control. For each cultivar, the experimental design was a split plot with four replicates, with fungicide as the main-plot factor and nozzle type as the sub-plot factor. In 2002 and 2003, the trial was conducted at Saskatoon and Outlook using two applications of chlorothalonil, azoxystrobin or pyraclostrobin. Tebuconazole was omitted from the study. The experimental design was changed to a factorial randomized complete block design with four replicates.

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2.2. Spray retention laboratory study The impact of different nozzle types on spray retention and canopy penetration was investigated using the same

chickpea cultivars as in the field study, Myles and Sanford. Single plants were grown in 10 cm diameter pots for 6 weeks in a greenhouse, by which time the plants had started to flower. Plants were brought to a track room and

Fig. 1. Area under the disease progress curve (AUDPC) in field experiments on chickpea evaluating the effect of three nozzle types used to apply fungicides. Bars represent standard errors of the means.

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Fig. 2. Chickpea yields in field experiments evaluating the effect of three nozzle types used to apply fungicides. Bars represent standard errors of the means.

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arranged in trays so that the canopy consisted of nine rows of nine pots with 20 cm between each row, and 11 cm spacing within rows, resulting in the standard plant density in the field of approximately 45 plants m2. At this density, the edges of plants were touching but foliage was not intertwined. A five-nozzle boom was fitted with the three nozzle types described in the field study at 50-cm spacing and traversed at 4.6 km h1. Boom height was 50 cm above the top of the canopy, and travelled in the same direction as the plant rows, as had been the case in the field study. Nozzles were calibrated with water for 30 s per nozzle, and spray pressure was adjusted to maintain equivalent output for all nozzles so that the same travel speed could be used. Spray pressures were 270, 280, and 290 kPa for the Standard, Twin and Venturi tips, respectively, delivering 200 l ha1. The spray mixture contained fluorescent tracer dye (Rhodamine WT, 1000 ppm) and a non-ionic surfactant (Agral 90, 0.1% v/v). Petri dishes (15 cm diameter) placed on either end of the plant canopy were used to determine the actual volume of solution applied. Each treatment was replicated six times. After the spray pass, the central tray of nine plants was removed from the track room. Plants were carefully removed from this tray to avoid cross-contamination until only the central plant remained. This central plant was cut into thirds by height and each section was divided into leaves and stems, resulting in six sub-samples per replicate plant. During this sampling the plants were held with forceps, and plant parts were cut directly into plastic containers subsequently used for dye extraction. The leaf and stem samples were washed by agitating in 100 ml (leaves) or 50 ml (stems) of 95% ethanol for 1 min. The concentration of tracer dye in a sub-sample of the ethanol wash was determined using fluorescence spectrophotometry (545 nm excitation and 570 nm emission). The quantity of liquid retained by the plants was normalized to 200 l ha1 by dividing the measured dye on plants by the proportion of 200 l ha1 captured in the Petri dishes for that

application. Normalization was done to account for slight differences in swath width or pattern uniformity delivered to the canopy with the three application methods. After washing, plant parts were oven-dried and weighed. The liquid retained by each plant part at each position in the canopy was expressed as the amount of spray liquid per g dry weight of plant material (ml g1), and data were analysed as a randomized complete block design. 2.3. Statistical analysis Disease severity data from the various rating dates were transformed into percentage data as described by Horsfall and Barratt (1945), and the area under the disease progress curve (AUDPC) was calculated (Shaner and Finney, 1977). Plant density data were analysed to ensure that differences among treatments were not confounded by a corresponding difference in plant density. All statistical analyses were conducted in the Statistical Analysis System (SAS) version 8 (SAS Institute Inc., Cary, NC, USA). Data were tested for normality and homogeneity of variance prior to analysis with the Mixed procedure (field data) or GLM procedure (retention data) in SAS. Heterogeneous variances were stabilized through transformation or modelled. Initial analysis tested whether fungicides had an effect on disease compared to untreated controls. Controls were then dropped from data sets to analyse the effects of the different fungicides and nozzle types. Means were separated by contrasts and by the least significant square method. Treatment effects were considered significant at P ¼ 0.05. 3. Results 3.1. Field study Ascochyta blight severity varied significantly among years and locations, allowing the effect of nozzle types to

Fig. 3. Severity of Ascochyta rabiei seed infection in chickpea from field experiments evaluating the effect of three nozzle types used to apply fungicides. Bars represent standard errors of the means.

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be assessed under conditions of low, intermediate and high disease pressure. Extremely low disease development with 4% ascochyta blight severity in control plots of both cultivars was observed at Saskatoon in 2001. Drought conditions also occurred at Scott, where disease levels in control plots of cultivar Myles only reached 10%, and 39% in those of Sanford. At Outlook under irrigation, 33%

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ascochyta blight severity was recorded in control plots of Myles, whereas disease levels of 83% were observed in Sanford. In 2002, a cool, dry spring resulted in late sowing and delayed emergence. Cool weather and frequent rains late in the season led to severe blight development at both sites. The final disease severity on Myles reached 78% at

Fig. 4. Thousand seed weights (TSWs) of chickpea in field experiments evaluating the effect of three nozzle types used to apply fungicides. Bars represent standard errors of the means.

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Outlook and 92% at Saskatoon, and 99% on Sanford at both sites. Wet conditions late in the season also led to delayed maturity, poor pod fill, and contributed to low seed yields, especially in plots of Sanford.

Despite dry conditions through much of the growing season in 2003, small isolated rain events were sufficient for moderate to high disease severity to develop at Saskatoon. Disease levels were about 45% in control plots of Myles

Table 2 P-values of the mixed model and contrast analyses to compare the effect of three fungicides and three nozzle types on ascochyta blight in chickpea (measured as area under the disease progress curve), yield, seed infection and thousand seed weight (TSW) in field experiments in Saskatchewan, Canada Source

Disease Myles

Yield Sanford

Myles

Seed infection Sanford

Myles

TSW Sanford

Myles

Sanford

Saskatoon 2001 Fungicide Nozzle Fungicide*Nozzle Standard vs. Twin Standard vs. Venturi Twin vs. Venturi

0.1114 0.4839 0.7058 0.7853 0.2520 0.3796

0.3329 0.6640 0.7762 0.4437 0.9787 0.4282

0.7324 0.0795 0.3309 0.4665 0.5801 0.8476

0.0003 0.1398 0.0014 0.0497 0.2963 0.3263

– – – – – –

– – – – – –

– – – – – –

Outlook 2001 Fungicide Nozzle Fungicide*Nozzle Standard vs. Twin Standard vs. Venturi Twin vs. Venturi

o0.0001 0.4703 0.5517 0.2447 0.4316 0.6707

0.0002 0.5719 0.7746 0.3075 0.6084 0.5814

0.0571 0.5782 0.6199 0.4426 0.8668 0.5300

0.0077 0.2509 0.9905 0.1269 0.7985 0.1920

– – – – – –

– – – – – –

0.5526 0.7116 0.1894 0.8057 0.4292 0.5817

o0.0001 0.1844 0.0139 0.1038 0.8874 0.1274

Scott 2001 Fungicide Nozzle Fungicide*Nozzle Standard vs. Twin Standard vs. Venturi Twin vs. Venturi

0.0480 0.4465 0.6101 0.3445 0.7957 0.2320

0.0696 0.5659 0.6840 0.3237 0.4494 0.7991

0.1300 0.4296 0.9626 0.2824 0.9567 0.2622

0.0002 0.1300 0.2439 0.1661 0.5343 0.0506

– – – – – –

– – – – – –

0.0417 0.4662 0.0545 0.5486 0.5241 0.2215

o0.0001 0.0299 0.1378 0.0106 0.0593 0.4125

Saskatoon 2002 Fungicide Nozzle Fungicide*Nozzle Standard vs. Twin Standard vs. Venturi Twin vs. Venturi

o0.0001 0.4132 0.3763 0.5022 0.1882 0.5073

o0.0001 0.6280 0.6864 0.5270 0.7566 0.3489

0.0002 0.7047 0.7876 0.4223 0.5673 0.8143

0.0001 0.4557 0.5334 0.2168 0.5577 0.5031

0.0013 0.7239 0.1949 0.4557 0.5383 0.8947

– – – – – –

– – – – – –

Outlook 2002 Fungicide Nozzle Fungicide*Nozzle Standard vs. Twin Standard vs. Venturi Twin vs. Venturi

o0.0001 0.0754 0.4879 0.4267 0.1307 0.0269

o0.0001 0.0667 0.0865 0.7956 0.567 0.0340

0.0281 0.6482 0.8388 0.9681 0.4370 0.4144

0.0001 0.7978 0.5278 0.5395 0.9321 0.5966

o0.0001 0.4061 0.9963 0.3292 0.7561 0.2020

Saskatoon 2003 Fungicide Nozzle Fungicide*Nozzle Standard vs. Twin Standard vs. Venturi Twin vs. Venturi

o0.0001 0.2370 0.6989 0.1144 0.7709 0.1906

o0.0001 0.1208 0.2802 0.0469 0.5118 0.1599

0.1235 0.6576 0.6441 0.9478 0.4142 0.4518

o0.0001 0.2341 0.2399 0.2349 0.1010 0.6306

– – – – – –

Outlook 2003 Fungicide Nozzle Fungicide*Nozzle Standard vs. Twin Standard vs. Venturi Twin vs. Venturi

o0.0001 0.0272 0.8509 0.0091 0.0660 0.3565

0.0001 0.6794 0.3283 0.7066 0.3886 0.6214

0.0618 0.3806 0.2382 0.2632 0.2065 0.8807

o0.0001 0.7219 0.9046 0.4501 0.5446 0.8795

– – – – – –

– – – – – –

– – – – – –

o0.0001 0.0404 0.0150 0.4272 0.0141 0.0784

0.0241 0.9355 0.8497 0.7713 0.9668 0.7398

– – – – – –

0.5090 0.4507 0.3225 0.7153 0.2224 0.3439

0.0002 0.6226 0.0319 0.3614 0.7739 0.5327

– – – – – –

0.9504 0.2411 0.8612 0.2288 0.1063 0.6639

0.0007 0.8731 0.9039 0.6450 0.9766 0.6661

0.2971 0.7613 0.0320 0.6199 0.8252 0.4749

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and 91% in Sanford. At Outlook, irrigation was used sparingly, and only a low level of disease developed. Disease levels reached 20% in control plots of Myles and 28% in Sanford plots. In general, fungicide applications reduced ascochyta blight severity on chickpea plants and increased yields in all trials compared to the untreated control, irrespective of product or nozzle type used for the application (data not presented). This effect was more prominent when disease pressure was high and in the more susceptible Table 3 Summary of analysis of variance for spray retention (ml g1) on three regions of the plant canopy (top, middle, bottom) and two plant parts (leaves, stems) of two chickpea cultivars using three nozzle types Source

df

Sums of squares

P value

Cultivar Nozzle Position Plant part Cultivar*Nozzle Cultivar*Position Cultivar*Plant part Nozzle*Position Nozzle*Plant part Position*Plant part Cultivar*Nozzle*Position Cultivar*Nozzle*Plant part Cultivar*Position*Plant part Nozzle*Position*Plant part Cultivar*Nozzle*Position*Plant part Block Error

1 2 2 1 2 2 1 4 2 2 4 2 2 4 4 5 157

34.78 6635.63 8260.91 370378.94 4378.96 4107.48 1625.89 5890.04 2818.12 7268.85 5378.62 472.58 442.24 6645.13 6904.99 1407.71 742736.66

0.0893 0.1817 0.1204 o0.0001 0.3232 0.3465 0.3595 0.5495 0.4825 0.1547 0.5939 0.8846 0.8915 0.4876 0.4674 0.9809

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cultivar Sanford (Figs. 1 and 2). Under high disease pressure, seed infection and TSW were significantly lower in fungicide-treated plots compared to control plots (Figs. 3 and 4). Experiments showed that in general the effect of nozzle types used for fungicide application was not influenced by the chickpea cultivar or the fungicide product (Table 2). Nozzle types only affected disease severity differentially in one of the seven trials. Under low disease pressure at Outlook in 2003 with 20% ascochyta blight severity in Myles at the end of the season, the Standard nozzle gave slightly less disease control compared to the Twin nozzles (Table 2, Fig. 1). There were no significant differences in yield between plots sprayed with different nozzles, nor did any nozzle type consistently affect seed infection rates and seed weight (Table 2, Figs. 2–4). 3.2. Spray retention laboratory study Spray deposition on Petri dishes placed in front of and behind the plant canopy averaged 158725 l ha1. Analysis of variance showed that spray deposition was not significantly affected by chickpea cultivar, nor by the nozzle used (Table 3). Both cultivars captured approximately 71 ml g1 dry weight when averaged over all nozzle types, canopy locations, and plant parts. Position within the canopy did not affect deposition significantly, whereas plant part affected spray deposition (Po0.001), with leaves retaining on average 115 ml g1 and stems retaining only 28 ml g1. All three nozzle types gave similar coverage of Myles and Sanford chickpea plants, and had similar canopy penetration (Fig. 5).

Fig. 5. Deposition of spray liquid (ml g1) applied with three different nozzle types on stems and leaves of chickpea. Bars represent standard errors of the means.

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4. Discussion In 2001, ascochyta blight levels were very low in most parts of Saskatchewan as a result of severe drought conditions, but disease development was moderate to high in irrigated plots at Outlook. Disease levels were extremely high at both sites in 2002, and ranged from low to high in 2003. Comparison of the Standard nozzle (flat fan nozzle TeeJet XR8002) with the Twin nozzle (Lurmark Twin Cap nozzles with two XR8001 tips) and the Venturi nozzle (Air Bubble Jet 11002) revealed that spray quality had no effect on ascochyta blight control irrespective of the severity of ascochyta blight and the chickpea cultivar. This result is similar to the work of Kutcher and Wolf (2006) in which conventional and air-induced sprays did not differentially affect sclerotinia disease or seed yield of canola with two fungicides over 5 site-years as long as spray pressure of the air-induced nozzles was sufficiently high. Spray deposition studies under controlled conditions confirmed that there was no difference in spray deposition among the nozzles, irrespective of the canopy architecture of the target plants. Similarly, spray retention studies on mustard and buckwheat sprayed with glyphosate revealed no effect of droplet size on control (Howarth et al., 2004). A reduction in spray deposition on vertical more so than on horizontal surfaces with larger spray droplets was observed in spray deposition studies on flat cut-grass swards (Webb et al., 2004). Unifoliate and fern leaf chickpeas exhibit distinct canopy architectures that were expected to influence spray penetration and spray deposition. Both chickpea types vary in the overall canopy morphology, leaf orientation, the surface area of the leaves and the structure of leaves. Unifoliate chickpea cultivars are characterized by a planophile canopy, a more horizontal orientation of the leaves, and an overall smaller surface area per leaf (Li, 2006). In contrast, fern-type chickpea cultivars are more erectophile, with more vertically oriented branches and leaves that also have a larger, but more discontinuous surface area compared to unifoliate leaves. Higher leaf area has been associated with higher spray deposition in barley (Jagers op Akkerhuis et al., 1998), but this is influenced by the position of the leaves. Wirth et al. (1991) showed that vertical barley leaves captured 80% of the spray from a flat fan nozzle that was retained on horizontal leaves. Droplets of less than 150 mm are primarily trapped by inertial impaction and are more likely deposited on vertical structures, but also on abaxial leaf surfaces (Bache, 1985). In contrast, droplets of more than 150 mm move primarily by sedimentation and thus would be expected to be trapped more often by horizontal leaves (Knoche, 1994). Although there are differences in branching and leaf angles among dicotyledonous plant species, the overall architecture of the plants remains complex. It may be, therefore, an over-simplification to classify canopies as horizontal and vertical, and to infer the differential effects of droplet sizes (Knoche, 1994), which may explain why no

differences among nozzles were observed in the current study. It has been suggested that leaf hairs, which are abundant in chickpea, can significantly improve impaction frequency (Spillman, 1984), but may reduce spray retention depending on the physico-chemical nature of the spray mixture (Holloway, 1970). On such difficult-to-wet surfaces, increased spray retention has been observed with smaller spray droplets in the droplet size range of 100–400 mm (Lake and Marchant, 1983). Indeed, when reviewing herbicide studies, Knoche (1994) found that in 71% of studies spray deposition increased with decreasing droplet size. In 21% of the studies there was no difference and in 9% of studies smaller droplets negatively affected spray deposition. Studies on strawberry indicated that fungicides sprayed at a fine spray quality with 181–186 mm VMD resulted in higher efficacy in controlling powdery mildew in midseason compared to a medium spray quality with 221–232 mm VMD (Cross et al., 2000). However, the final powdery mildew severity was not significantly different between plots of both treatments. Debroize and Denoirjean (2000) found no effect of droplet size on speedwell control using a contact herbicide. In contrast, Howarth et al. (2004) reported that while droplet size did not influence the efficacy of glyphosate in broad-leaved mustard, smaller droplet sizes were more efficacious in controlling the more erect and difficult-to-wet wild oats. They concluded that droplet size effects became more pronounced at lower water volumes, particularly for the grassy species. In conclusion, field studies and laboratory spray retention studies showed that spray quality did not influence the performance of fungicides in controlling ascochyta blight. Based on these findings, it is appropriate to recommend fungicide application with coarse spray qualities, as these reduce spray drift potential without affecting efficacy. Acknowledgments Funding provided by the Saskatchewan Pulse Growers is gratefully acknowledged. We also acknowledge support from BASF, Syngenta, and Bayer CropScience. Technical support was provided by Heather Deobald, Teri Ife, Gerry Stuber, Allan MacDonald, Clint Ringdal, and Don David. Thanks also to the field crew at the AAFC Scott Research Farm. References ASABE, 2004. Spray Nozzle Classification by Droplet Spectra (ASAE S572 FEB04). ASABE Standards, St. Joseph, MI , pp. 437–440. Bache, D.H., 1985. Prediction and analysis of spray penetration into plant canopies. In: Southcombe, E.S.E. (Ed.), Application and Biology, BCPC Monograph No. 28. BCPC Publications, Croydon, pp. 183–190. Chongo, G., Gossen, B.D., 2001. Effect of plant age on resistance to Ascochyta rabiei in chickpea. Can. J. Plant Pathol. 23, 358–363. Cross, J.V., Berrie, A.M., Murray, R.A., 2000. Effect of droplet size and spray volume on deposits and efficacy of strawberry spraying. In:

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