Effect of fungicide application technology on seed yield in field pea under variable Mycosphaerella blight pressure

Abstract

Mycosphaerella blight, caused by Peyronellaea pinodes (Berk. & A. Bloxam) Aveskamp, Gruyter & Verkley (syn. Mycosphaerella pinodes (Berk. et Blox.) Vesterg.), is a destructive foliar pathogen of field pea that is managed, in large part, through application of foliar fungicide at flowering. The fungicides are usually applied into dense crop canopies, so reaching the lower areas of the canopy where the pathogen is initially most active is a challenge. Field trials were conducted across the Canadian prairies from 2008 to 2011 to assess the efficacy of various nozzle numbers and orientations, droplet sizes, and water volumes for the management of Mycosphaerella blight to increase yield in field pea. Pea plants were assessed for disease severity during flowering and seed yield was measured. In 10 of the 13 trials, double-nozzle configurations provided a 15% reduction in disease severity and up to a 60% increase in yield. In contrast, droplet size and angle of application had no effect on field pea yield. Water volume trials using up to 400 L ha⁻¹ improved fungicide efficacy relative to control treatments, however, volumes above 400 L ha⁻¹ resulted in high-disease severity and lower yield, likely as a result of fungicide run-off due to saturation of the leaf surface. When deciding on effective sprayer techniques for fungicide application, disease pressure, environmental conditions and cultivar characteristics are important to consider.

Résumé

L’anthracnose, causée par Peyronellaea pinodes (Berk. & A. Bloxam) Aveskamp, Gruyter & Verkley (syn. Mycosphaerella pinodes [Berk. et Blox.] Vesterg.), un agent pathogène destructeur qui s’attaque au feuillage des pois potagers, est gérée en grande partie par l’application de fongicide foliaire au stade de la floraison. Les fongicides sont généralement appliqués sur le couvert végétal dense, ce qui constitue un défi, parce que le produit n’atteint pas les parties basses de la plante où l’agent pathogène est d’abord le plus actif. De 2008 à 2011, des essais au champ ont été menés partout sur les Prairies canadiennes afin d’évaluer l’efficacité de différents nombres de buses et de leurs orientations, de la grosseur des gouttelettes et des volumes d’eau pour maîtriser l’anthracnose en vue d’accroître le rendement du pois potager. Les plants de pois ont été évalués en fonction de la gravité de la maladie au stade de la floraison, et le rendement en graines a été déterminé. Dans 10 des 13 essais, des configurations de buses à double jet ont permis de réduire de 15% la gravité de la maladie et d’accroître le rendement jusqu’à 60%. En revanche, la grosseur des gouttelettes et l’angle d’application n’ont eu aucun effet sur le rendement. Les essais sur les volumes d’eau ont démontré que, jusqu’à 400 L ha⁻¹, l’efficacité du fongicide était accrue par rapport aux traitements de contrôle. Toutefois, les volumes supérieurs à 400 L ha⁻¹ ont entraîné une augmentation de la gravité de la maladie et de plus faibles rendements, probablement à cause du ruissellement du fongicide engendré par la saturation de la surface foliaire. Lorsqu’il s’agit de prendre des décisions quant à la bonne façon d’appliquer les fongicides, le risque de maladie, les conditions climatiques et les caractéristiques du cultivar doivent être pris en considération.

Keywords:

• Mycosphaerella blight
• Mycosphaerella pinodes
• nozzles
• Peyronellaea pinodes
• Pisum sativum
• sprayer technology

Mots clés:

• Anthracnose
• Mycosphaerella pinodes
• Peyronellaea pinodes
• Pisum sativum
• buses
• technologie des pulvérisateurs

Introduction

On the northern Great Plains of North America, field pea (Pisum sativum L.) provides an alternative to cereals and canola in cropping rotations, with the added benefit of lowering input costs due to the plants ability to fix atmospheric nitrogen. An increased emphasis on soil health and crop diversification on commercial farms over the last 30 years has led to substantial increases in pulse crop production across Canada’s prairies.

Mycosphaerella blight, caused by Peyronellaea pinodes (Berk. & A. Bloxam) Aveskamp, Gruyter & Verkley (syn. Mycosphaerella pinodes (Berk & A. Bloxam) Vestergr), anamorph Ascochyta pinodes (Berk. & Blox.) Jones, is a destructive foliar pathogen of field pea in western Canada and around the world (Beasse et al. 1999; Davidson and Ramsey 2000; Banniza and Vandenberg 2003; Bretag et al. 2006). At early growth stages, damaging lesions on the leaves and stems interfere with photosynthesis and plant vegetative development, while at later stages the pathogen causes crop lodging and the lesions on reproductive structures such as flowers and pods affect seed quality and yield (Bretag et al. 2006). Yield losses vary considerably, but have been reported to be as high as 50% in Canada (Conner et al. 2007). Peyronellaea pinodes is part of the Ascochyta blight complex, which comprised four fungal pathogens: A. pisi (Chilvers et al. 2009), P. pinodes, Phoma pinodella (L.K. Jones) Morgan-Jones & K.B. Burch and Phoma koolunga (Davidson et al. 2009). Of the four, P. pinodes is the most abundant in western Canada, causing 95% of the Ascochyta blight infections (Bowness et al. 2016).

Avoidance strategies such as crop rotation are important for the management of plant pathogens, especially those that are residue borne (Peairs et al. 2005; Davidson and Kimber 2007). However, wind-borne ascospores of P. pinodes are widely dispersed and provide an effective source of primary inoculum in the region (Gossen et al. 2010). Current low-till land management practices present challenges for reducing the amount of available inoculum and, as a result, multiple applications of foliar fungicide, initiated at early to mid-flowering, are required to provide effective disease reduction and improve yield (Beasse et al. 2000; Warkentin et al. 2000). Yield increases between 15% and 75% have been consistently reported in field experiments where P. pinodes has been managed with fungicides (Xue et al. 2003; Bretag et al. 2006). Pyraclostrobin, a strobilurin fungicide, has been widely used on many crops in the region since 2002. It is the active ingredient in Headline 250 EC fungicide (BASF Canada, Mississauga, ON) that provides broad-spectrum control of many plant pathogens (Karadimos et al. 2005), including the Ascochyta and Peyronellaea spp. on pulse crops (BASF 2020). Prior research showed 94% of P. pinodes isolates are sensitive to pyraclostrobin fungicide (Bowness et al. 2016).

The majority of sprayers on commercial farms on the northern Great Plains utilize single flat-fan or hollow-cone hydraulic nozzles. A tapered flat-fan nozzle design is most common because it provides a uniform spray pattern and minimum spray drift (Elliot and Mann 1997). Most sprayers are set up to optimize herbicide application on young weeds, where the targets are horizontal surfaces at the top of the canopy. Fungicides are generally applied with the minimum water volume possible, but are most effective when targeted for the entire canopy (Gossen et al. 2008). Fungicides are very important in crop disease management and represent about 21% of pesticide use in the world (Steurbaut 1993). In Canada, pesticide use has increased from 7% in 1996 to 23% in 2011 (Gossen et al. 2014).

When applying crop protection agents, the objective is to place sufficient active ingredient at the appropriate growth stage to achieve the desired biological result on the target tissue safely and economically (Ebert et al. 1999). There are a number of factors affecting safe, effective application of fungicides, from the spray solution properties to the active ingredient in the target system (Wirth et al. 1991). One aspect is efficacy, which is determined by the uptake and effectiveness of the active ingredient combined with the degree of coverage of the target plant (Edgington 1981; Armstrong-Cho et al. 2008a). Plant coverage is affected by the architecture of the plant such as number and size of leaves, plant height, stem strength, leaf surface characteristics, characteristics of the spray mixture, carrier water volume, droplet size, and spray angle (Gossen et al. 2008).

Droplet size is an important component of pesticide application, with benefits associated with the use of both small and large droplets (Grover et al. 1997). Finer sprays provide a greater number of smaller droplets that are easily carried by airflow resulting in better coverage, and because of their size are less likely to run off (Cross et al. 2001). In general, small droplet size provides better leaf coverage and retention. As a result, protectant fungicides are generally most effective when applied as small droplets that evenly cover both sides of the leaf surface (Knoche 1994). In contrast, systemic fungicides move within leaf tissue and so may be most effective when applied in larger droplets (Bateman 1993; Elliot and Mann 1997). The movement of small droplets is largely dependent on the target crop, the spray system, meteorological conditions, and the plant canopy. However, small droplets do not penetrate the canopy as well and are readily displaced by wind, so they contribute to the majority of off-target drift (Spillman 1984; Wolf et al. 1993; Wilson 2007). Smaller droplets can also mean faster evaporation rates (Wolf 2011).

A double-nozzle system for spray application can improve the spray pattern for finer sprays, provide greater pesticide efficacy and reduce the dilution of the product on the leaf surface compared to a single nozzle (Hall et al. 1996). The orientation of the two nozzles can also affect penetration of the active ingredient into crop canopies. Double nozzle spray application combinations can include a nozzle delivering water directly down (vertical) combined with a nozzle spraying at an angle, both nozzles spraying vertically, or both nozzles spraying at an angle (one pointed forward and one backward). Often, one nozzle produces a coarse spray and the second a fine spray. Use of a double-nozzle system can reduce application volumes by 30–50% in many host--pathogen systems as a consequence of better coverage (Chapple et al. 1997). Double nozzles combined with coarse sprays and lower boom height provided better coverage for fungicides on canola (Brassica napus L.) and wheat (Triticum aestivum L.) crops (Dietz 2013). The results can be most effective if the fine spray nozzle contains the active ingredient and delivers it into the water spray cloud (Ebert and Downer 2006). Double nozzles have been recommended to optimize the coverage of vertical targets, such as the growing tips of many pulse crops (Wolf 2011).

Increasing the water carrier volume in sprayer systems can improve penetration into the crop and increases the frequency of droplets at all levels of the canopy. Higher volumes also have the added benefit of decreasing the potential for drift and increasing nozzle performance (Wirth et al. 1991). For management of Mycosphaerella blight in field pea, application at early flowering, when the crop canopy is already closed, makes fungicide delivery to the target tissues in the lower canopy challenging. An increase in fungicide carrier volume reduced Ascochyta blight severity in chickpea (Cicer arietinum L.) under moderate-to-high disease pressure (Armstrong-Cho et al. 2008b) and improved leaf and fruit coverage in apple orchards (Cross et al. 2001).

It is important to deliver and retain the active ingredient at critical sites at sufficient rates to inhibit the target pathogen (Gossen et al. 2008). Specific combinations of droplet size, nozzle orientation, and carrier volume may increase the efficacy of foliar fungicides against Mycosphaerella blight, but data on the effect of these factors is limited. The objective of this study was to assess the efficacy of selected component of the delivery system for foliar fungicide application, especially droplet size, nozzle orientation, and carrier volume to optimize reduction in Mycosphaerella blight severity on field pea.

Materials and methods

Field studies

Nozzle configurations and angles. Field trials were conducted at the Agriculture and Agri-Food Canada Research and Development Centres at Morden (MB), Saskatoon (SK), and Lacombe (AB), and at the Crop Diversification Centre North, Alberta Agriculture and Forestry, Edmonton (AB) from 2008 to 2011. These four sites represent the main areas of field pea production on the Canadian prairies. Treatments varied between locations and evolved over the study years as described in Table 1. All trials included an untreated control where plots were inoculated with the pathogen, but no fungicide treatments were applied.

Table 1. List of treatments used to apply pyraclostrobin fungicide to field pea in two field studies (1 and 2) conducted at Morden, MB, Saskatoon, SK, Lacombe, AB and Edmonton, AB, from 2008 to 2011

Nozzle^a		Droplet size	Angle	Study 1 (6 station years)	Study 2 (7 station years)
Single
ER8002		fine	vertical	X	X
MR8002		coarse	vertical	X	X
ER8001^b		fine	vertical	X
ER8002		fine	60°		X
MR8002		coarse	60°		X
Double
ER8001	ER8001	fine	vertical	X	X
DR8001	DR8001	coarse	vertical	X	X
ER8001	DR8001	fine/coarse	60°/vertical	X	X
ER8001	ER8001	fine	60°	X	X
DR8001	DR8001	coarse	60°	X	X
Control				X	X

^aComboJet™ nozzles – ER (extended range), MR (mid-range), and DR (drift reduction) with a flat fan pattern spraying at an 80° angle from the nozzle tip. Nozzles ending in −02 have higher output than nozzles ending in-01.

^bWater carrier volume applied at 100 L ha⁻¹. All other treatments were applied at 200 L ha⁻¹.

The initial study (Study 1) to compare the efficacy of single- and double-nozzle treatments was conducted in Morden in 2008, 2009, and 2010, and Saskatoon in 2008 and 2009 (two trials with different field pea cultivars). The treatments were pyraclostrobin fungicide (Headline EC, BASF Canada) applied at early flowering using selected combinations of ComboJet™ nozzles (ER, extended range; MR, mid-range; DR, drift reduction) with a flat fan pattern (Westward Parts, Red Deer, AB) and an 80° angle of dispersion from the nozzle tip, unless otherwise specified (Table 1). In a second study (Study 2), one double-nozzle treatment and a treatment with reduced carrier volume from Study 1 were replaced with three treatments applied at a 60° forward angle from the nozzle tip (Table 1). Two trials were conducted at Lacombe and two at Edmonton in 2009, and one trial at Saskatoon and two at Lacombe in 2011.

Each trial was laid out in a randomized complete block design (RCBD) with four replications. Each plot consisted of four rows (Morden, Lacombe, and Edmonton) or eight rows (Saskatoon). Row spacing varied from 25 cm to 30 cm, depending on seeding equipment and were seeded to establish a target plant density of 85–90 plants m⁻². As a result, plots varied in size across locations (7.5 m² at Morden, 9 m² at Edmonton and Lacombe, 15 m² at Saskatoon).

Several field pea cultivars were assessed to test fungicide delivery on different canopy structures. Cultivar choice represented different plant characteristics found in field pea such as vine length (plant height), leafy versus semi-leafless types, stem thickness, leaf size, leaf shape, length between nodes, days to flowering and maturity (related to disease avoidance) and other characteristics that would affect disease management. The use of multiple cultivars contributed to a robust data set considering these characteristics. The descriptive terms that describe these characteristics are industry standards used in provincial Seed Guides, based in comparison with widely grown registered cultivars and standard check cultivars provided to assist growers in cultivar choice. For Mycosphaerella blight, terms such as ‘poor’, ‘fair’, ‘good’, and ‘very good’ are used. For lodging, a scale of 1 to 9 is used where 1 = erect and 9 = flat.

Field pea ‘Topper’ was grown in the trials at Morden in 2008, 2009 and 2010 (Study 1); at Saskatoon in 2011 (Study 2); at Edmonton in 2009 and at Lacombe in 2009 and 2011 (Study 2). Topper is a yellow, early maturing cultivar with poor resistance to Mycosphaerella blight and has a tendency to lodge (Ali-Khan 1991). The cultivar ‘Delta’ was used in Saskatoon in 2008 (Study 1). ‘Delta’ is a yellow pea that has fair Mycosphaerella blight resistance (Anderson et al. 2002) and fair resistance to lodging (5.1 out of 9) (Saskatchewan Seed Guide; Saskatchewan Seed Growers Association 2010). Cultivar ‘Carneval’ was used at Edmonton in 2009 and at one of the sites at Lacombe in each of 2009 and 2011 (Study 2). ‘Carneval’ is a yellow, semi-leafless, medium maturing cultivar with moderate Mycosphaerella blight resistance (Anderson et al. 2002; Xue and Warkentin 2001) and fair lodging resistance (3.5 out of 9).

The cultivars ‘Nitouche’ and ‘CDC Montero’ were used in separate trials at Saskatoon in 2009 (Study 1) to compare treatments in an upright crop canopy vs. one more likely to lodge. ‘Nitouche’ is a green, semi-leafless, medium maturing cultivar with fair Mycosphaerella blight resistance (Warkentin et al. 2006) and good lodging resistance (2.8 out of 9) (Saskatchewan Seed Guide; Saskatchewan Seed Growers Association 2007). ‘CDC Montero’ is a green, semi-leafless, medium maturing cultivar with fair Mycosphaerella blight resistance (Vandenberg et al. 2002) and fair lodging resistance (5.1 out of 9) (Saskatchewan Seed Guide; Saskatchewan Seed Growers Association 2009).

Initial weed control was obtained by application of soil-applied trifluralin (Loveland Products, Loveland, CO) or ethalfluralin (Dow AgroSciences Canada Inc., Calgary, AB) at the recommended rates in the previous fall or early spring. In-crop applications of bentazon (BASF Canada, Mississauga, ON), sethoxydim (BASF Canada) or imazethapyr (BASF Canada) were applied at the recommended rates and timing. The plots were then hand-weeded as necessary. Overhead irrigation was applied at Saskatoon in 2009 to initiate disease infection under very dry environmental conditions. Seedling emergence was counted to ensure uniformity within the plots.

Plots were inoculated using one of two methods, depending on location, with both methods having demonstrated efficacy in previous studies. In Morden, Saskatoon, Lacombe and Edmonton, crop residues were collected from a previous field pea crop with a heavy infestation of Mycosphaerella blight and applied evenly to the entire trial before the canopy closed. In addition, plots at Edmonton and Lacombe were inoculated with a spore suspension of P. pinodes applied using a hand pump sprayer at the early flowering stage to target good disease establishment. The isolates used were collected the previous year from surveys conducted in Alberta. The isolates were grown on commercial potato dextrose agar (Difco Laboratories, Detroit, IL, USA) in Petri dishes for 14 d under white fluorescent light at 20°C (± 2°C) with 16 h light/8 h dark. The dishes were flooded with 5 mL of water and spores were dislodged with a glass rod and/or a small transfer loop. The resulting raw spore suspension from each dish was filtered through two layers of commercial cheesecloth and combined into a single-spore suspension. The concentration was adjusted to 2 × 10⁵ spores mL⁻¹, 0.05% Tween® 20 was added, and the solution was sprayed onto plants until run-off.

The foliar fungicide pyraclostrobin was applied at a rate of 100 g a.i. ha⁻¹ with a backpack sprayer in a carrier volume of 250 L ha⁻¹ of water at Saskatoon, Edmonton and Lacombe, and at 200 L ha⁻¹ at Morden (unless otherwise stated). Each nozzle combination was calibrated to 210–275 kPa before initial application. The fungicide was applied either once (at the early flowering stage when symptoms were noted) or twice (once at the early flowering stage and once 10–14 d later at the mid-flower to early pod stage). The timing of applications depended on Mycosphaerella blight severity at each location, and fungicide was delayed if disease was not present. Fungicide was applied according to presence of the pathogen, disease level, crop canopy moisture, environmental conditions, risk of pathogen spread (Lopetinsky and Strydhorst 2002) and the appropriate recommended growth stage of the crop (Warkentin et al. 1996).

Ten pea plants were selected from each plot and whole plants were assessed for severity of Mycosphaerella blight symptoms based on leaf lesion damage (%). The foliage and stems were examined and rated on a 0–9 scale, where 0 = no disease symptoms and 9 = the plant was completely covered with lesions (Xue et al. 1996). Ratings were taken just before fungicide application and again approximately every 7 d until plant senescence. Plots were harvested at physiological maturity using a small plot combine. Seed was air-dried, cleaned, weighed, and yield determined.

Carrier volume and nozzle number. Field trials were conducted at Saskatoon, SK, and Lacombe, AB, in 2010 and 2011 to examine the effect on yield of selected water volumes and nozzle number to control Mycosphaerella blight. Treatments were rates of carrier volume, applied with single or double nozzles (Table 2) and varied slightly between locations.

Table 2. List of nozzle treatments and carrier volumes used to apply pyraclostrobin fungicide in field and growth chamber trials at Saskatoon, SK, and Lacombe, AB, in 2010 and 2011

Nozzle^a		Volume (L ha^−1)
Single
ER8002	–	50
ER8002	–	100
ER8004	–	200
ER8008	–	400
ER8025	–	800
Double
ER8001	ER8001	50
ER8001	ER8001	100
ER8002	ER8002	200
ER8004	ER8004	400
ER8015	ER8015	800
Control

^aComboJet ™ nozzles – ER (extended range) with a flat fan pattern spraying at an 80° angle from the nozzle tip. Nozzles ending in −01 have lowest output and output increases as number increases with nozzles ending in −25 having the highest output.

The trials were arranged in a RCBD, seedling emergence was counted, weeds were controlled, and plots were inoculated, rated and harvested as described previously. Plot size was 7.5 m² at Saskatoon (four rows per plot) and 9 m² in Lacombe. Plots were seeded with the cultivar ‘Cutlass’ to achieve a target density of 85–90 plants m⁻². ‘Cutlass’ is a yellow, semi-leafless, medium maturing variety with fair Mycosphaerella blight resistance, very good powdery mildew resistance, and good lodging resistance (Blade et al. 2004; Saskatchewan Seed Growers Association (Saskatchewan Seed Guide) 2011). Plots were inoculated using one of two methods, depending on location, as described previously. The foliar fungicide pyraclostrobin was applied at a rate of 100 g a.i. ha⁻¹ with a backpack sprayer at the various water volume treatment rates. Each nozzle combination was calibrated to 210–275 kPa before initial application. The fungicide was applied twice; once at the early flowering stage and once 10–14 d later at the mid-flower to early pod stage.

Growth chamber study

An experiment was conducted under controlled conditions in a growth chamber to assess the effect of the same nozzles, arrangements and carrier volume treatments as in the field trials (Table 2) on levels of P. pinodes severity on inoculated ‘Cutlass’ field pea. Pure mass-transfer cultures of selected pathogenic isolates of P. pinodes were inoculated onto 50 Petri dishes containing commercial potato dextrose agar medium and grown for 1 week with a 16 h photoperiod under fluorescent light at 20°C (± 2°C). The isolates were collected the previous year from surveys conducted in Alberta and Saskatchewan. After 7 d, conidia were harvested from each dish as described previously.

The experiment was arranged in a RCBD with four replications (pots). Each 15 cm diameter pot of soilless mix (Premier Horticultural Canada Inc., Riviere-de-Loupe, QC) was thinned to 10 plants after emergence and placed in a growth chamber at 16 h photoperiod and 15°C (± 2°C).

Pyraclostrobin fungicide was applied to the pots 21 d after planting at an equivalent field rate of 100 g a.i. ha⁻¹ (5 mL per pot) and corresponding field water volume equivalents (0.5–8 L). Treatments were applied with a backpack sprayer in a confined area under controlled conditions. Pots were inoculated 2 d later by spraying plants with a spore suspension of 2 × 10⁵ spores mL⁻¹ until run-off with a hand-held spray bottle containing a pre-determined amount of water (enough to cover the leaves and stems until run-off). After inoculation, the pots were transferred into a clear plastic humidity chamber and maintained at high relative humidity for 48 h with a 16 h photoperiod at 15°C (± 2°C). After removal from the humidity chamber, the plants were returned to the growth chamber, where the humidity was kept as high as possible with the use of a cool air electrostatic humidifier. Each plant was rated for lesions of P. pinodes at 7 d, 14 d, and 21 d after inoculation using the 0–9 percentage rating scale developed by Xue et al. (1996) as described previously. Yield data were not collected.

Data analysis

The statistical analyses were a mixed model analysis of variance conducted using PROC MIXED, in SAS 9.2 (SAS Institute Inc., Cary, NC, USA). Differences were considered significant at p ≤ 0.05. Residuals were tested for normality using the Shapiro-Wilk test, and for homogeneity prior to analysis. Minor heterogeneous variances were modelled using the mixed procedure in SAS (Gomez and Gomez 1984). Application treatment, cultivar and their interactions were considered fixed effects. Replication, year and location, as well as interactions with fixed effects, were considered random effects. Given that the disease ratings were generated using a 0–9 scale (Xue et al. 1996) and represent a continuous data set, disease ratings were not statistically analysed. Ratings are presented in combination with statistically analysed yield data to illustrate disease pressure and provide information to support treatment efficacy.

Yield data were initially analysed within site year. Data were pooled for analysis across locations and years whenever the treatment structure was similar and cultivar had no effect on yield (SAS 2011). Differences in the number of treatments between the two field studies made the suitability of combining data from all treatments across all sites questionable, since blocks of different sizes would have different inter- and intra-block variation, affecting proper allocation of error in PROC MIXED analysis (SAS 2011; Yang, personal communication). Therefore, similar treatments were pooled across years and locations where possible.

Treatments were examined in a combined analysis across all of the site years; the effect of fungicide application on yield was compared with the nontreated control and other treatments using a single degree of freedom orthogonal contrast. Where this contrast was significant in the nozzle orientation study, treatments at a vertical orientation were analysed as a factorial design with nozzle number (single vs. double) and droplet size (fine vs. coarse) as the fixed effects. Similarly, sites that included treatments at a high angle of orientation were combined for locations where fungicide reduced blight severity and yield analysed as a factorial design with nozzle number, droplet size and orientation (vertical vs. high angle) as the fixed effects.

In the carrier volume and nozzle configuration trials, all treatments except the nontreated control were analysed for yield as a factorial design with nozzle number (single vs. double) and water volume (50–800 L ha⁻¹) as the fixed effects.

Plant density was assessed to verify that the stands were uniform (± 10%) and that differences among treatments were not confounded by plant population. Disease ratings were collected and initial analyses of seed yield explored for differences among fungicide application treatments with different nozzle configurations and water volumes. The treatment means were then compared using the differences between least square means method (Steel et al. 1997). Single degree of freedom contrasts (although not always orthogonal) were used to compare the seed yield of pre-determined differences among logically corresponding treatments and each treatment to the control.

The data from the carrier volume trials and growth chamber trials were tested for first and second degree polynomial response (linear and quadratic, respectively) for disease severity and the carrier volume trials were tested for yield using orthogonal polynomial coefficient contrasts (Steel et al. 1997) to assess the response to application rates.

For all field studies, a Pearson correlation of disease severity with seed yield was calculated using PROC CORR in SAS 9.2 (SAS Institute Inc., Cary, NC, USA) for each location. Fungicide application treatments were combined to identify a relationship between observed final disease ratings and final yield. The correlation coefficients were considered significant at p ≤ 0.05.

Results

Field studies

Nozzle configurations and orientation. In the trials at Morden (Study 1) using ‘Topper’, there were no differences among treatments observed for disease severity and no significant differences for yield in 2008 or 2010. Growing conditions in 2008 were abnormally dry, and the severity of Mycosphaerella blight was low. In 2009, despite dry conditions, there were differences among treatments with the double nozzle system and a significant negatively correlated relationship between disease severity and yield (Table 9). The double nozzle fine-spray treatments had the lowest observed blight severity (Supplemental Table S1) and highest seed yield. The control treatment yielded 3.60 T ha⁻¹, which was significantly lower than the double nozzle fine-spray (4.47 T ha⁻¹), double nozzle – coarse spray (4.33 T ha⁻¹), and double nozzle – both fine- and coarse-spray treatments (4.39 T ha⁻¹) (Table 3, Supplemental Table S1). Yield in the double nozzle coarse-spray treatment was also significantly higher than the single nozzle coarse-spray treatment (3.74 T ha⁻¹) (Table 3). In 2010, blight severity was high as a result of very wet conditions. There were no differences observed for severity, no significant differences in yield and no significant correlation among the data points (Table 9), but (as it was in 2009) the double nozzle fine-spray treatment had the lowest final disease severity ratings (Supplemental Table S1). When the data from ‘Morden’ were combined across all years, the double-nozzle treatment with one fine and one coarse nozzle was the only treatment that differed from the nontreated control (data not shown).

Table 3. The effect of pyraclostrobin fungicide application treatments at Morden, MB, Saskatoon, SK, Lacombe, AB, and Edmonton, AB, from 2008 to 2011 based on orthogonal contrasts of least square means

Year	Location	Cultivar	Treatment A	Yield	Treatment B		Yield	Pr > |t|
				(T ha^−1)	Nozzle	Angle	(T ha^−1)
2008	Saskatoon	Delta	control	1.90	single-fine	vertical	2.22	0.0060
			control	1.90	double-fine	vertical	2.15	0.0265
2009	Morden	Topper	control	3.60	double-fine	vertical	4.47	0.0052
			control	3.60	double-coarse	vertical	4.33	0.0156
			control	3.60	double-both	both	4.39	0.0100
			single-coarse	3.74	double-coarse	vertical	4.33	0.0442
2009	Saskatoon	Nitouche	control	3.60	double-coarse	vertical	4.06	0.0148
			single-fine	4.01	double-fine	vertical	3.53	0.0118
			double-fine	3.53	double-both	vertical	3.90	0.0212
		Nitouche/Montero	control	4.01	double coarse	vertical	4.38	0.0136^a
			single-coarse	4.07	double coarse	vertical	4.38	0.0347^a
2009	Edmonton	Topper	control	1.75	single-fine	vertical	2.06	0.0212
			control	1.75	double-fine	vertical	2.17	0.0034
			control	1.75	single-fine	high	2.12	0.0084
			control	1.75	single-coarse	high	2.10	0.0112
			control	1.75	double-fine	high	2.20	0.0205
			control	1.75	double-coarse	high	2.07	0.0018
		Topper/Carneval	control	2.00	double-fine	vertical	2.35	0.0234^a
			control	2.00	double-coar	high	2.20	0.0146^a
2009	Lacombe	Topper	control	1.47	single-fine	vertical	2.04	0.0161
			control	1.47	single-coarse	vertical	2.42	0.0002
			control	1.47	double-fine	vertical	2.00	0.0231
			control	1.47	double-coarse	vertical	2.33	0.0012
			control	1.47	single-fine	high	2.37	0.0004
			control	1.47	single-coarse	high	2.32	0.0008
			control	1.47	double-fine	high	2.38	0.0004
			control	1.47	double-coarse	high	2.21	0.0025
2011	Lacombe	Topper	control	1.72	single-fine	vertical	2.62	0.0029
			control	1.72	single-coarse	vertical	2.53	0.0009
			control	1.72	single-fine	high	2.66	0.0196
			control	1.72	single-coarse	high	2.33	0.0003
			control	1.72	double-fine	high	2.78	0.0013
			control	1.72	double-coarse	high	2.62	0.0010

Single nozzle either mounted in a vertical position from the boom (vertical) or mounted at a 60° angle (high). Double nozzles (two nozzle) either mounted in a vertical position from the boom (vertical) or mounted at a 60° angle (high). Nozzles delivered either a small droplet size (fine) or a large droplet size (coarse).

^aPooled data.

Table 4. Analysis of variance (fixed effects) of pyraclostrobin fungicide application treatments and cultivar effects on yield on two studies in 2009

Location	Cultivars	Effect	Num DF	Denom DF	F value	Pr > F
Saskatoon	Montero/Nitouche	Treatment (T)	6	39	1.89	0.1072
(Study 1)		Cultivar (C)	1	39	81.27	< 0.0001
		T*C	6	39	0.67	0.6766
Edmonton	Carneval/Topper	Treatment (T)	8	51	1.52	0.1748
(Study 2)		Cultivar (C)	1	51	22.44	< 0.0001
		T*C	8	51	1.02	0.4349

Treatments including single and double nozzles, vertical and high angles, fine and coarse spray droplets.

Table 5. Mycosphaerella blight severity and seed yield following selected treatments for application of pyraclostrobin fungicide on field pea cv. Topper at Lacombe, AB, in 2009 and 2011 (Study 2)

	2009			2011
	Severity rating^a		Yield	Severity rating^a		Yield
Nozzle type and angle	20-Aug	26-Aug	(T ha^−1)	2-Aug	25-Aug	(T ha^−1)
Single Nozzle
- fine spray	7.9	8.2	2.04^b	5.4	5.6	2.62^b
- coarse spray	8.1	8.1	2.42^b	5.1	5.5	2.53^b
- fine spray, 60° angle	8.1	8.4	2.37^b	5.2	5.7	2.66^b
- coarse spray, 60° angle	8.0	8.2	2.32^b	5.5	5.4	2.33^b
Double Nozzle
- fine spray	7.6	8.0	2.00^b	5.4	5.6	2.25^b
- coarse spray	8.0	8.3	2.33^b	4.9	5.4	2.17
- fine spray, 60° angle	7.7	7.7	2.38^b	5.0	5.4	2.78^b
- coarse spray, 60° angle	8.0	8.5	2.21^b	5.4	5.6	2.62^b
Control	8.5	8.8	1.47	5.7	5.8	1.72

^aVisual ratings using a scale of 0–9 (Xue 1996).

^bYield significantly different than nontreated control at p ≤ 0.05 using Proc Mixed in SAS 9.2.

Table 6. Effects of pyraclostrobin fungicide application treatments on seed yield of field pea cv. Topper at Lacombe, AB, in 2009 and 2011 based on orthoganol contrast of pooled least square means (Study 2)

Treatment A	Yield (T ha^−1)	Treatment B	Yield (T ha^−1)	Estimate	Pr > |t|
single fine	2.33	single fine – 60°	2.52	−163.54	0.2984
single coarse	2.51	single coarse – 60°	2.32	167.77	0.2869
double fine	2.13	double fine – 60°	2.58	−407.83	0.0605
double coarse	2.23	double coarse – 60°	2.42	−171.04	0.2782

Table 7. Factorial analysis of variance (fixed effects) of pyraclostrobin fungicide application treatment effects on Topper pea yield at Morden, MB, Saskatoon, SK, Lacombe and Edmonton, AB, in 2008–2011 (Study 1 and 2, pooled data)

Treatments^a	Effect^b	Num DF	Denom DF	F value	Pr > F
2–5	Nozzle number (N)	1	70	0.01	0.9306
	Droplet size (S)	1	70	0.01	0.9036
	N*S	1	70	0.01	0.9951
2–5 and 8–11^c	Nozzle number (N)	1	82	0.16	0.6945
	Droplet size (S)	1	82	0.07	0.7955
	N*S	1	82	0.00	0.9512
	Angle (A)	1	82	3.63	0.0603
	N*A	1	82	1.49	0.2264
	S*A	1	82	1.16	0.2844
	N*S*A	1	82	0.29	0.5913

^aTreatments: 2 = a single nozzle, producing a fine spray, vertical position; 3 = a single nozzle, producing a coarse spray, vertical position; 4 = double nozzles, producing a fine spray, vertical position; 5 = double nozzles, producing a coarse spray, vertical position; 8 = a single nozzle, producing a fine spray, 60° angle; 9 = single nozzle, coarse spray, 60° angle; 10 = double nozzles, fine spray, 60° angle, and 11 = double nozzles, coarse spray, 60° angle.

^bNozzle number including single and double nozzles, droplet size including fine and coarse spray droplets, and angles including vertical and high (60°).

^cTreatments 8–11 were included in the analysis at sites tested and when sdf contrast was significant at p ≤ 0.05.

Table 8. Orthogonal contrast analysis of least square means for yield response to pyraclostrobin fungicide carrier volume application treatments at Lacombe, AB, in 2010 and 2011

Year	Treatment A	Treatment B			Std
		Nozzle	Volume (L ha^−1)	Estimate	Error	t-value	Pr > |t|
2010	control	single nozzle	100	−615.70	180.45	−3.41	0.0028
	control	single nozzle	400	−477.70	180.45	−2.65	0.0155
	control	double nozzles	200	−474.53	179.41	−2.64	0.0155
2011	control	single nozzle	800	−1020.75	369.39	−2.76	0.0097
2010/2011	control	single nozzle	800	−746.31	225.76	−3.31	0.0079

Table 9. Pearson correlation analysis results of Mycosphaerella disease severity ratings and yield to pyraclostrobin fungicide application treatments and carrier volumes at Morden, Saskatchewan, Lacombe, and Edmonton, 2008 to 2011

Test	Year	Location	Cultivar	N	r	p
Study 1	2008	Saskatoon	Delta	28	−0.67	0.0181
	2009	Morden	Topper	28	−0.56	0.0018
		Saskatoon	Nitouche	28	−0.37	0.0512
	2010	Morden	Topper	28	−0.34	0.0744^a
Study 2	2009	Edmonton	Topper	36	−0.26	0.1233^a
		Lacombe	Topper	35	−0.14	0.4220^a
	2011	Lacombe	Topper	36	−0.07	0.6596^a
Carrier Volume	2010	Lacombe	Cutlass	44	−0.80	<.0001
	2011	Lacombe	Cutlass	44	−0.27	0.0767^a

^aNot significantly correlated at p ≤ 0.05 using Proc Corr in SAS 9.2.

In 2008 at Saskatoon (Study 1), conditions were dry and not conducive for disease establishment and spread. Mycosphaerella blight was negatively correlated with yield (Table 9), was most severe on ‘Delta’ in the nontreated control with a mean score of 7.3 and lowest in the treatments containing a double nozzle, fine spray with a mean score of 5.8 (Supplemental Table S2). Yield in the double nozzle with a fine spray was higher than the control (2.2 vs. 1.9 T ha⁻¹), as was the single-nozzle treatment with a fine spray (2.2 T ha⁻¹). In 2009, ‘CDC Montero’ was seeded at two sites (Site 1 and Site 2) and ‘Nitouche’ was seeded adjacently, at Site 1 (Study 1). At this site, final blight severity was observed to be slightly lower in the double nozzle fine spray and double nozzle coarse-spray treatments than the other treatments with ‘CDC Montero’, but there were no significant differences in yield (data not shown). This is likely due to the dry conditions with low blight severity levels that did not progress and affect yield. In the trial using ‘Nitouche’, Mycosphaerella blight severity and yield were moderately negatively correlated (Table 9). Disease ratings were observed to be lower (with a mean score of 6.2 vs. 7.9) and yield significantly higher (4.1 vs. 3.6 T ha⁻¹) for the double nozzle coarse-spray treatment compared to the control (Table 3; Supplemental Table S3). The single nozzle fine spray (4.0 T ha⁻¹) and double nozzle fine- + coarse-spray (3.9 T ha⁻¹) treatments were observed to have lower disease ratings (5.8 and 6.4, respectively) and were more effective than the double nozzle fine-spray treatment (mean disease score of 6.6) for yield (3.5 T ha⁻¹) (Table 3; Supplemental Table S3). The two trials conducted at the same site, one with ‘CDC Montero’ and the other with ‘Nitouche’, were pooled and analysed together. There was a significant cultivar effect, but no effect of application treatment and no interaction (Table 4). The double nozzle coarse-spray treatment was more effective than a single nozzle coarse spray and the nontreated control (Table 3).

In Edmonton in 2009 (Study 2), conditions were dry, disease severity was low, and there were no yield differences in the trial with ‘Carneval’. In the trial with ‘Topper’, however, blight severity was lowest with a mean score of 4.6 in the double nozzle fine spray – 60° treatment (Supplemental Table S4). Although not significantly correlated with disease levels (Table 9), several spray treatments had higher yield than the nontreated control (Table 3). The results with this cultivar indicated that increasing the angle of the spray increased the effectiveness of the fungicide. When cultivar data were combined, the results confirmed that the double nozzle fine spray and double nozzle coarse spray, high angle treatments had higher yield when compared to the control (Table 3). There was a significant cultivar effect (Table 4) verifying the difference in response, and no interaction. This confirmed that although the cultivars responded differently, the treatment response remained the same.

At Lacombe in both 2009 and 2011 (Study 2), there were no notable differences in blight severity and no significant differences in yield in the trial with ‘Carneval’. As in Edmonton in 2009, conditions were abnormally dry and disease severity was low for that cultivar. In 2011, despite excess moisture early in the season, conditions were dry after canopy closure, and severity was moderate (Table 5). In trials using ‘Topper’, however, significant differences occurred for yield in both years, under contrasting disease pressure, although in neither year were disease ratings correlated with yield response (Table 9). Mycosphaerella blight severity was observed to be lower, ranging from an overall mean value of 8.2 in 2009 and 5.5 in 2011for all treatments when compared with the control (8.8 and 5.8). The lowest severity was noted in the double-nozzle treatments, especially when combined with a fine spray (7.7 in 2009 and 5.4 in 2011) (Table 5). For yield, there were significant differences between the nontreated control and all other treatments in both years, except for the double nozzle coarse spray in 2011 (Table 3; Table 5). When yield data for ‘Topper’ were combined across years, all of the treatments were significantly better than the control (Fig. 1). Treatments applied at a 60° angle did not differ from the same treatment applied at the lower angle (Table 6). The data from Lacombe and Edmonton in 2009 were combined and analysed to determine the effect of cultivar. The results confirmed the observations of the individual site years, where there was no response on ‘Carneval’ but a significant response for yield on ‘Topper’ for all treatments compared with the control. The combined effect of treatment was not significant, but the effect of cultivar was with no interaction between the two (data not shown).

Fig. 1 Yield response of field pea cultivar ‘Topper’ following selected application treatments of pyraclostrobin fungicide at Lacombe, AB, in 2009 and 2011 (pooled data). sing = single nozzle; fine = fine droplet size; coar/cor = coarse droplet size; doub/dob = double nozzles; ha = applied a 60° angle. Capped line = standard error

At Saskatoon in 2011 (Study 2), Mycosphaerella blight severity on ‘Topper’ was moderate to high throughout the season, but there were no treatment differences noted for blight severity and no significant differences for seed yield.

Factorial analysis of pooled selected sites (including single nozzle fine spray, single nozzle coarse spray, double nozzle fine spray, and double nozzle coarse spray) of ‘Topper’ detected no differences or interactions in yield among the treatments (Table 7).

Carrier volume and nozzle configuration. In 2010 at Lacombe, under wet conditions, disease severity ratings were strongly negatively correlated with yield (Table 9) and the lowest final disease severity on ‘Cutlass’, with a mean score of 7.4, was observed in the double nozzle – 200 L ha⁻¹ treatment (Supplemental Table S5). When compared to nontreated control (1.0 T ha⁻¹), yield for the single nozzle – 100 L ha⁻¹ (1.7 T ha⁻¹), single nozzle – 400 L ha⁻¹ (1.6 T ha⁻¹) and double nozzle – 200 L ha⁻¹ (1.5 T ha⁻¹) treatments were significantly higher (Table 8). In addition, there was a quadratic (non-linear) response to increasing carrier volume for the double nozzles; yield increased up to 200 L ha⁻¹ and then decreased for the 400 and 800 L ha⁻¹ rates (Fig. 2). In 2011, under wet conditions, yield of the single nozzle – 800 L ha⁻¹ (3.5 T ha⁻¹) treatment was significantly higher than the nontreated control (2.3 T ha⁻¹) (Table 8). Disease ratings were not correlated with yield (Table 9), no other differences were observed and no additional polynomial trends were detected.

Fig. 2 Yield response of field pea cutlivar ‘Cutlass’ in response to water carrier volumes of pyraclostrobin fungicide applied with double nozzles in a field trial at Lacombe, AB, in 2010

When the data for the two years of trials in Lacombe were combined, results were similar to the individual years. Yield was higher in the single nozzle – 800 L ha⁻¹ treatment than the nontreated control as observed in 2011 (Table 8), and there was a quadratic response to increasing carrier volumes applied using double nozzles as seen in 2010 (Fig. 2). Yield increased between the 50 and 100 L ha⁻¹ rate, levelled off between 200 L ha⁻¹ and 400 L ha⁻¹, and decreased at 800 L ha⁻¹.

In the trial at Saskatoon in 2010, blight severity was moderate to high with excess moisture early in the growing season, but conditions became drier later in the season and the disease did not progress. There were no differences observed in severity and no yield differences among the treatments. In 2011, conditions were dry from pre-bloom to harvest. As a result, blight severity was low and there were no differences observed for disease severity or yield (data not shown).

There were no differences among treatments or interactions based on factorial analysis when results from all sites were pooled (data not shown).

Growth chamber study

There was a quadratic response to increasing volumes applied with either single or double nozzles under controlled conditions in Lacombe. Disease severity decreased up to the 200 L ha⁻¹ carrier volume and then increased as the volume increased to 400 and 800 L ha⁻¹ (Fig. 3).

Fig. 3 Negative quadratic effect of nozzle orientation and water carrier volumes with single and double nozzles of fungicide applications on Mycosphaerella blight severity (0–9 scale) on the pea cultivar ‘Cutlass’ in a growth chamber experiment (pooled across repetitions). Pyraclostrobin was applied to 21-day-old plants at an equivalent field rate of 100 g a.i. ha⁻¹ (5 mL per pot) and corresponding field water volumes (0.5 L, 1 L, 2 L, 4 L, 8 L)

Discussion

These studies examined 10 combinations of nozzles and application angles over four locations, with six cultivars and five carrier volumes on two cultivars for a total of 17 station years. Variation among location, treatments, seasonal growing conditions, plot management, and cultivar influenced the epidemiology of the disease and impacted final yield leading to variability in the results, thus making it difficult to identify the most effective treatment for fungicide application. However, overall conclusions were defined and trial results indicate that a double nozzle configuration may be beneficial for management of Mycosphaerella blight on field pea.

The majority of sprayer systems on commercial farms utilize single hydraulic nozzles applying fungicides in as minimum water volumes as possible. Tapered flat-fan nozzle designs are most common because they provide uniform spray patterns with minimum spray drift (Elliot and Mann 1997; Gossen et al. 2008). Most agrochemical systems are set up to deliver herbicides, focussing on coverage of horizontal surfaces at the top of the canopy for systemic products applied to small plants. However, fungicidal products require adequate delivery throughout the entire crop canopy. Considering that fungicides constitute a significant portion of farm input costs, modifying spray application technology could significantly change the economics for many operations. Fungicides are effective tools for disease management and it is important to apply them as efficiently and economically as possible.

Hall et al. (1996) reported that the use of double nozzles over a single nozzle improved the spray pattern for finer sprays, provided greater pesticide efficacy, and reduced the dilution of the product on the leaf surface. Double nozzles combined with coarse sprays and lower boom height provided improved coverage for fungicides on canola (Brassica napus L.) and wheat (Triticum aestivum L.) (Dietz 2013). In 10 of the 13 nozzle combination trials, double nozzle configurations gave 15% better control of Mycosphaerella blight than the nontreated control. Single-nozzle treatments were generally intermediate, but often did not improve disease ratings relative to the control. In many cases, these small differences in blight severity were not correlated with yield, but double-nozzle treatments produced higher yields than the nontreated control in 6 of 17 station years (Table 3). Across locations and years, there were three instances where there were differences among the treatments when the control treatment was removed. In two of these instances, a double-nozzle treatment increased yield relative to the single-nozzle treatment with the same droplet size pattern (Table 3).

Droplet size is an important component of fungicide application with many factors affecting efficacy. Smaller droplets have better leaf coverage, better retention and studies show better pesticide efficacy (Knoche 1994; Cross et al. 2001). However, larger droplets penetrate the canopy better, are more readily absorbed, have a significant positive impact on disease levels and seem to be more effective overall because of the lower risk of drift and evaporation (Maybank et al. 1990; Feng et al. 2003). For Mycosphaerella blight, infection is initiated in the lowest portion of the crop canopy, so penetration of the fungicide into the canopy is important. These studies show both fine- and coarse-nozzle treatments generally resulted in similar disease reduction relative to the control. These findings are similar to those for A. rabiei (Pass.) L. on chickpea (Armstrong-Cho et al. 2008a) and Sclerotinia sclerotiorum (Lib.) de Bary on canola (Kutcher and Wolf 2006), where droplet size had no effect on disease levels.

Previous studies indicate that at least one nozzle should be placed at an angle when fungicides are being applied because canopy penetration is best at that orientation (Wolf 2011; Dietz 2013). The results from 2009 at Morden and Edmonton, under dry conditions, indicated that a high nozzle orientation angle (60°) reduced Mycosphaerella blight severity, which was correlated with improved yield, particularly on the cultivar ‘Topper’. However, at other locations and years, application at a lower angle was just as effective. Pooled data from Lacombe in 2009 and 2011 showed a decrease in disease severity that was not correlated with final yield. This indicates that vertical application is as effective as angled application. Factors such as disease pressure and cultivar characteristics such as standability, leaf type and plant height appear to be more important for management of Mycosphaerella blight than the application angle of the fungicide.

In these studies, disease pressure and the cultivar characteristics were important factors in disease management and had an important impact on the efficacy of fungicide application. The effect of cultivar is likely due to differences in vine length (plant height), leaf type, stem thickness, leaf size, leaf shape, length between nodes, days to flowering, maturity, and particularly its tendency to lodge. When data were combined across sites, cultivar response always differed, even when the same treatments were applied in the same year in adjacent trials. The cultivar ‘Carneval’, which has moderate resistance to P. pinodes and resists lodging, did not show any treatment differences, whereas ‘Topper’ with poor resistance to P. pinodes and a tendency to lodge, often exhibited differences among treatments. There are no cultivars completely resistant to P. pinodes, but cultivars with reduced susceptibility and better lodging resistance may reduce the need to adjust nozzle systems for best efficacy. Cultivars that have a greater tendency to lodge may be easier to target than a standing crop. The negative impacts of lodging on yield is exacerbated by P. pinodes infection (Wang et al. 2006), making disease management even more important in wet years or when a cultivar has reduced lodging resistance. In contrast, cultivar did not have a significant effect in fungicide application studies on chickpea (Armstrong-Cho et al. 2008b), which rarely lodges.

Under low to moderate disease pressure, as seen in Saskatoon in 2010 and 2011, water carrier volume did not affect blight severity or impact seed yield. In contrast, under higher disease pressure, increasing the carrier volume up to 200 L ha⁻¹ reduced blight severity and increased yield (Lacombe in both years). However, larger volumes (up to 800 L ha⁻¹) progressively increased severity and reduced yield compared with lower fungicide application rates (although not always significant). This is consistent with previous reports that an increase in fungicide carrier volume up to a certain level reduced severity under moderate-to-high disease pressure (Cross et al. 2001; Armstrong-Cho et al. 2008b). In field and controlled environment studies that examined a range of water volumes, there were no differences between single and double nozzles and no interaction between them.

Increasing the carrier volume improves penetration into the crop and increases the frequency of droplets at all levels of the canopy. Larger volumes have the added benefit of decreasing the potential for drift, improving nozzle performance (Wirth et al. 1991) and increasing product efficacy of fungicides (Wolf et al. 1993). If water volumes are not high enough to maintain adequate droplet densities, aspects of spray targeting and fungicide formulation may be compromised (Steurbaut 1993; Jensen et al. 2001). Some fungicides will work effectively on crops using lower volumes, but it appears that with pyraclostrobin on field pea, moderate-to-higher volumes are optimum providing application rates are not excessively high.

There are numerous factors involved in optimizing the application of fungicides from formulation to fungicide mode of action. The results of these studies show that double nozzles may provide an advantage for management of Mycosphaerella blight when applying fungicide in moderate carrier volumes (100 to 200 L ha⁻¹). However, applying the correct fungicide at the appropriate time and rate, not investigated in this study, is even more important to achieve optimal disease management in any cropping system. Ultimately, superior fungicide application depends on the knowledge, care, and judgement of the sprayer operator.

Acknowledgements

The authors thank K. Bassendowski, T. Dubitz and L. Schnepf for technical assistance, BASF for providing fungicide, Dr. T. Wolf, AAFC Saskatoon, for nozzles and recommendations on treatment selection, and the Alberta Pulse Growers for partial funding of the project.

Supplemental material

Supplemental data for this article can be accessed online here: https://doi.org/10.1080/07060661.2021.1872868