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The interaction of annual weed and white mold management systems for dry bean production in Canada

Publication: Canadian Journal of Plant Science
1 January 2011

Abstract

Pynenburg, G. M., Sikkema, P. H., Robinson, D. E. and Gillard, C. L. 2011. The interaction of annual weed and white mold management systems for dry bean production in Canada. Can. J. Plant Sci. 91: 587–598. Annual weeds and white mold (Sclerotinia sclerotiorum) are serious pests in dry bean, and can cause substantial yield losses. The proper management of these pests is essential for profitable production. A 2-yr study conducted at three field locations in Ontario examined the effects of two pre-plant incorporated herbicide programs on weed management and three foliar fungicides on white mold development. In addition, thiamethoxam was evaluated for its ability to alleviate stress caused by annual weeds and white mold. Interactions among disease severity, weed control, agronomics and economic returns were examined. Thiamethoxam seed treatment had inconsistent benefits with respect to plant emergence and vigour, harvested weight, seed weight and economic returns. There were no benefits for the other parameters measured. The premium herbicide program (s-metolachlor plus imazethapyr) reduced weed ground cover, white mold severity and pod drop, and increased 100-seed weight, harvested weight and net economic return compared with the economic herbicide program (trifluralin). The foliar fungicides reduced white mold severity and pod drop, while increasing 100-seed weight, harvested yield and net economic return. Fluazinam resulted in the lowest white mold severity, and the highest yield and treatment return, when compared with cyprodinil/fludioxonil and boscalid in some environments. High weed pressure in the presence of white mold increased disease severity. Where treatment differences occurred, the premium herbicide program and fluazinam foliar fungicide resulted in the highest net economic return to growers.

Résumé

Pynenburg, G. M., Sikkema, P. H., Robinson, D. E. et Gillard, C. L. 2011. Interaction des systèmes de lutte contre les mauvaises herbes annuelles et contre la moisissure blanche dans les cultures de haricot sec au Canada. Can. J. Plant Sci. 91: 587–598. Les adventices annuelles et la moisissure blanche (Sclerotinia sclerotiorum) posent de sérieux problèmes dans les champs de haricot et peuvent donner lieu à de sérieuses baisses de rendement. Il est donc essentiel de lutter correctement contre eux pour parvenir à une culture lucrative. Les auteurs ont entrepris une étude de deux ans sur le terrain, à trois sites de l'Ontario en vue de préciser les répercussions de l'incorporation de deux herbicides de pré-levée au sol sur les mauvaises herbes et l'incidence de trois fongicides foliaires sur le développement de la moisissure blanche. D'autre part, ils ont déterminé dans quelle mesure le thiaméthoxame parvenait à atténuer le stress attribuable aux adventices annuelles et à la moisissure blanche. Dans cette optique, ils ont examiné les interactions entre la gravité de la maladie, le désherbage, divers paramètres agronomiques et le rendement économique. Le traitement des semences avec du thiaméthoxame ne présente pas d'avantages cohérents au niveau de la germination et de la vigueur des plants, ni en ce qui concerne le poids à la récolte, le poids des graines et le rendement économique. Les autres paramètres examinés n'en bénéficient pas davantage. Comparativement au programme de désherbage le plus économique (trifluralin), le programme de désherbage le plus coûteux (s-métolachlor additionné d'imazethapyr) diminue la couverture de mauvaises herbes, la gravité de la moisissure blanche et la perte de gousses, tout en rehaussant le poids de 100graines, le poids à la récolte et le rendement économique net. Les fongicides foliaires diminuent la gravité de la moisissure blanche et la perte de gousses tout en accroissant le poids de 100graines, le poids à la récolte et le rendement économique net. Comparativement à l'application de cyprodinil/fludioxonil et de boscalid dans certaines conditions, l'application de fluazinam est le fongicide qui réduit le plus la gravité de la moisissure blanche et donne lieu au meilleur rendement ainsi qu'au plus haut rendement économique pour les traitements. La forte pression des mauvaises herbes en présence de moisissure blanche accroît la gravité de la maladie. Quand il y a une différence entre les traitements, c'est le programme de désherbage le plus coûteux et l'application foliaire du fluazinam qui procurent le meilleur rendement économique aux producteurs.
Dry bean (Phaseolus vulgaris L.) can be a profitable crop for agricultural producers, but requires a high level of management due to various stresses (Graham and Ranalli 1997). Weed interference in dry beans can result in yield losses of up to 85%, since dry beans are poor competitors with weeds (Blackshaw and Esau 1991; Malik et al. 1993; Chikoye et al. 1995; Wall 1995; Sikkema et al. 2008). The primary herbicides used for early-season weed control by Ontario dry bean producers are trifluralin, S-metolachlor and imazethapyr (Hall, B., Ontario Ministry of Agriculture, Food and Rural Affairs, 2010, personal communication). Trifluralin is a dinitroaniline (Group 3) herbicide, S-metolachlor is a chloroacetamide (Group 15) herbicide and imazethapyr is an imidazolinone (Group 2) herbicide. Under certain unfavourable environmental conditions, crop injury has been reported with the use of imazethapyr (Wilson and Miller 1991; Renner and Powell 1992; Arnold et al. 1993; Bauer et al. 1995; Blackshaw and Saindon 1996; Vencill 2002; Sikkema et al. 2004; Soltani et al. 2004, 2006). Crop injury depends on application rate, application timing, market class and cultivar (Vencill et al. 1990; Renner and Powell 1992; Blackshaw and Saindon 1996; Ward and Weaver 1996; VanGessel et al. 2000). In a related study, imazethapyr reduced plant height, shoot dry weight and yield in otebo beans, while trifluralin and S-metolachlor did not cause measurable crop injury. (Sikkema et al. 2006). The authors concluded that there was potential for imazethapyr injury in the small seeded market classes of dry beans.
White mold is a destructive disease caused by an invasive fungal pathogen [Sclerotinia sclerotiorum (Lib.) de Bary] that can infect up to 408 plant species (Boland and Hall 1994; Schwartz et al. 2006) in 65 families (Purdy 1979). Dry bean is one of the host species that is susceptible to white mold (Wallen and Sutton 1967; Haas and Bolwyn 1972; Purdy 1979; Tu and Beversdorf 1982; Steadman 1983; Boland and Hall 1994; CABI/EPPO 1999; Schwartz et al. 2006). Potential dry bean yield losses from white mold can vary from trace to 100% (Steadman 1983; Tu 1989; Schwartz et al. 2006). Favourable environmental conditions can account for 85% of the potential white mold incidence in dry bean (del Rio and Harikrishnan 2005; Harikrishnan and del Rio 2005). The environmental conditions in southwestern Ontario have been found to be highly conducive to white mold disease development, which can result in substantial but unpredictable yield losses (Wallen and Sutton 1967; Hass and Bolwyn 1972; Tu 1989). The average incidence of white mold in Ontario is 25%, and ranges from trace to 100% (Tu 1989). White mold severity in Ontario is also influenced by cultural practices and sclerotial density in the growing area (Tu 1997), resistant cultivars (Tu and Beversdorf 1982), biological control (Tu 1997) and chemical controls (Morton and Hall 1982).
The proper method and timing of application of a chemical fungicide has been an effective way to reduce yield losses due to white mold (Morton and Hall 1982; Tu 1997). Fungicides should be applied at early bloom, and if conditions continue to be conducive to disease development, a second application may be necessary (Vieira 2004). Fungicide timing is critical to protect immature (white) to mature (yellow) blossoms from infection. Appling fungicides to non-irrigated pinto and navy bean crops infected with white mold in North Dakota increased yields by up to 33%, and decreased white mold incidence by up to 42% (del Rio et al. 2004).
The efficacy of the foliar fungicides boscalid, fluazinam and cyprodinil/fludioxonil for the control of white mold in dry bean has been extensively studied. Boscalid is a Group 7 fungicide, and is part of the chemical Group pyridine-carboxamides. It was the most efficacious product in several studies (Vieira et al. 2001; Kee et al. 2004; Huang and Erickson 2007). Fluazinam is a Group 29 fungicide, and is part of the chemical Group 2,6-dinitro-anilines. It provided the best white mold control in a number of studies (Paula Jr. et al. 2006, 2009a, b; Varner and Terpstra 2007). Cyprodinil is a Group 9 fungicide, and it is part of the chemical Group aniline-pyrimidines. Fludioxonil is a Group 12 fungicide, and is part of the chemical Group phenyl pyrroles. The combination of these two fungicides provided superior white mold control in one study (Shah et al. 2002), while boscalid, fluazinam and cyprodinil/fludioxonil all reduced white mold severity equally in one study (Everts and Zhou 2007). Substantial evidence exists to document the efficacy of boscalid, fluazinam and cyprodinil/fludioxonil for white mold control in dry beans.
Cultural practices, including plant population, row width and weed control, impact white mold in dry beans. Increasing plant densities from 25 to 60 plants m−2 generally resulted in higher white mold pressure (Steadman et al. 1973; Park 1993; Saindon et al. 1995). In two related studies, the yield increases from higher plant populations outweighed any associated yield losses caused by white mold (Saindon et al. 1995; Blackshaw et al. 2000). A reduction in white mold was achieved by reducing plant densities and using fungicides (Paula Jr. et al. 2009a). In a similar study, a foliar fungicide (fluazinam) was needed in narrow rows with increased plant populations to counteract the associated white mold pressure to maximize yields, compared with wider rows and lower populations (Vieira et al. 2005). Weed population provided a similar effect to an increase in crop density, in that higher weed densities within the crop increased white mold severity (Blackshaw et al. 2000), by limiting air movement and trapping moisture within the crop canopy, as well as providing increased contact between infected and uninfected plants (Dillard and Hunter 1986; Blackshaw et al. 2000). Herbicide (Tharp et al. 2004; Soltani et al. 2007a; Sikkema et al. 2008) and fungicide (Harikrishnan et al. 2008) applications applied to control weeds and white mold, respectively, generally provided higher incomes to growers. Therefore, appropriate herbicides and fungicides are required to maintain a weed- and disease-free environment for dry bean production, particularly in narrow rows.
Thiamethoxam is a neonicotinoid insecticide with positive chemical and biological properties (Yamamoto 1996). Thiamethoxam can be applied as a seed treatment (ST), in-furrow application or foliar application on many crops in Canada. It controls soybean aphid Aphis glycines (Matsumura), bean leaf beetle Cerotoma trifurcate (Forster), potato leaf hopper Empoasca fabae (Harris) and cucumber beetle Diabrotica undecimpunctata (Howardi) in dry beans [Calafiori and Barbieri 2001; Maloney, T. S., Agri-Tech Consulting, 2002, unpublished; Nault et al. 2004; Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) 2007]. In addition to thiamethoxam's insecticidal properties, it has been reported to improve plant vigour in the absence of insect pests (Lebun, T., Syngenta Crop Protection Canada Inc., 2008, personal communication) which could potentially improve plant emergence, competition with weeds, stress tolerance and yield. Thiamethoxam has been shown to increase plant emergence and nodulation (Calafiori and Barbieri 2001), but increases in early plant development may have been due to the control of insect pests (Hofer et al. 2000). At times, the benefits are seen visually but are hard to measure objectively (Maloney, T. S., Agri-Tech Consulting, 2002, unpublished), or at all (Lourencao et al. 2003). No known published literature was found that studied the effect of thiamethoxam on plant vigour. Syngenta Crop Protection is conducting numerous experiments worldwide to quantify the effect of thiamethoxam on plant vigour (Lebun 2009, personal communication). More consistent benefits of thiamethoxam on plant vigour have been observed in dicot than monocot crops, and the benefits were more pronounced under abiotic stress conditions (Lebun 2009, personal communication). In addition to thiamethoxam's role as an effective insecticide in numerous crops, some evidence exists that suggests there is a plant vigour effect as well.
The potential return on investment from the application of a pesticide is an important consideration for dry bean growers. The benefits of herbicide application are influenced by knowledge of weed species composition, weed density, crop tolerance, and proper application timing (Forcella et al. 1996; Renner et al. 1999; O'Donovan et al. 2004; Tharp et al. 2004). Harikrishnan et al. (2008) studied the economic impact of white mold in North Dakota by surveying 250 fields between 2003 and 2005. Yield losses averaged 524 kg ha−1 (range 424–722 kg ha−1), which equates to an average economic loss of $2.95 million (range U.S. $0.63–5.74 million) per year. Profitability of a fungicide application for white mold control was influenced by disease pressure and varied between years. In years with high disease pressure, a fungicide application resulted in a positive return in 72% of the fields; but under medium to low disease-pressure, applying fungicides was a profitable practice in less than 20% of fields. Therefore, pest density and application timing are the key factors that influence the potential return on investment for pesticides in dry beans.
The objective of this research was to investigate the agronomic and economic benefits of a pest management program for dry bean production in Ontario. This study focused on three crop inputs; insecticide seed treatment, herbicide programs and preventative white mold foliar fungicide programs. The objectives were quantified by evaluating the pesticides for efficacy, improvements in crop emergence, vigour, yield and economic returns.

MATERIALS AND METHODS

Twelve field studies were conducted over a 2-yr period (2007 and 2008) in major dry bean growing areas in Ontario, Canada. Locations included the University of Guelph, Huron Research Station near Exeter, Honeywood Research Farm near Plattsville, and University of Guelph, Ridgetown Campus near Ridgetown. The soil type at Exeter was a Brookston clay loam soil (pH 7.8, organic matter 4.4%, sand 30%, silt 44% and clay 26%), at Plattsville was a Honeywood silt loam soil (pH 6.2. organic matter 3.2%, sand 37%, silt 52% and clay 12%), and at Ridgetown was a Brookston loam soil (pH 7.3, organic matter 4.5%, sand 45%, silt 29% and clay 26%). Primary tillage in Exeter consisted of fall plowing, while Plattsville and Ridgetown consisted of fall chisel plowing. All locations were cultivated twice in the spring.
Each experiment was established as a split plot, randomized complete block design with four replications at all locations. The study consisted of three factors: two insecticide seed treatments (none and thiamethoxam), two herbicide treatments (trifluralin and s-metolachlor/imazethapyr) and four fungicide treatments (none, fluazinam, cyprodinil/fludioxonil and boscalid). There were three sites (Ridgetown, Exeter and Plattsville) for 2 yr (2007 and 2008) and two environments were planted at each site in each year. The experimental units were 6 m long, but the width of each plot varied from 2.29 m at Exeter, to 2.67 m at Plattsville, to 1.14 m at Ridgetown. Great northern bean seed (cv. Beryl) was seeded in rows spaced 38 cm apart. Insecticide seed treatments (ST) consisted of an untreated control and thiamethoxam applied at 50 g a.i. 100 kg−1 seed. Thiamethoxam was applied to the seed 30–40 d prior to planting with a Hege 11 seed treater (Wintersteiger Inc. 4705 Amelia Earhart Drive Salt Lake City, UT). Preplant incorporated (PPI) herbicide treatments included trifluralin applied at 0.6 kg a.i. ha−1, and a tank mix of s-metolachlor plus imazethapyr applied at 1.14+0.045 kg a.i. ha−1. These herbicide treatments will be referred as the economic and premium herbicide program, respectively. The herbicide treatments were selected to provide a range in treatment effect for weed control. A zero herbicide control treatment was not included, as this would not be an appropriate management strategy for a conventional dry bean production system. The herbicides were applied to the soil surface 1 d prior to planting and incorporated with two passes of a field cultivator approximately 10 cm deep, with a travel speed of 10–13 km h−1 (OMAFRA 2006). The herbicides, fungicides and insecticides were applied with a CO2-pressurized backpack sprayer calibrated to deliver 200 L ha−1 of spray solution at a pressure of 200 kPa using Teejet 8002 flat-fan nozzles (Spraying Systems Co., P.O. Box 7900, Wheaton, IL) spaced 0.5 m apart.
Fungicide treatments included fluazinam at 500 g a.i. ha−1, cyprodinil/fludioxonil at 609 g a.i. ha−1 and boscalid at 539 g a.i. ha−1. The first application was applied at 20 to 30% bloom representing an average of three mature (yellowed) flowers on a plant, and the second application was made 2 wk later. All foliar applications were made with a water volume of 200 L ha−1. In total there were 16 treatments, which included all possible combinations of insecticide, herbicide and fungicide treatments. Each pesticide was applied at the label rate, except imazethapyr, which was applied at 60 g a.i. ha−1, which represents 60% of the manufacturer's labelled rate. The reduced rate was meant to avoid potential plant injury from imazethapyr applied at label rate (Soltani et al. 2007b).
Studies were planted at two environments at each location in each year. Environment one was planted on Jun. 15, and environment two was planted on Jul. 01. These dates are generally later than most Ontario growers would plant, but the intention was to delay flowering to late August when morning dew periods are heavy, to encourage white mold development. Seed was planted to a depth of 5 cm at a rate of approximately 520 000 seeds ha−1. All trials had sclerotia fruiting bodies applied at a rate of 60 kg ha−1. The sclerotia were sourced from nearby commercial production fields.
Ontario fertilizer recommendations were used to determine fertilizer requirements for each environment (OMAFRA 2009), with the exception of nitrogen. Nitrogen was applied at 100 kg ha−1, which is higher than OMAFRA recommendations to promote additional crop growth. Experiments were maintained insect free by applying a foliar insecticide (lambda-cyhalothrin at 9.96 g a.i. ha−1) when potato leaf hoppers reached an economic threshold according to Ontario recommendations (OMAFRA 2009). The threshold values are based on leaf hopper nymph counts per leaf, and vary from 0.25 at the unifoliate leaf stage of dry bean developmental, 0.5 nymphs at 2nd–4th trifoliate leaf stage, 1.0 nymphs at 4th trifoliate to first bloom, and 2.0 nymphs after first bloom. Insecticide applications were repeated 2 wk later if insect pressure was above the economic threshold. Insecticide was applied to eliminate the confounding effect of insect pressure on the insecticide seed treatments. Azoxystrobin (125 g a.i. ha−1) was applied if anthracnose was present in the trial.
Plants emerged were counted at 1, 7 and 14 d after emergence (DAE), and divided by the number of seeds planted per row to determine percent emergence. Plant vigour was assessed at 7 and 14 DAE using a scale of 1–10 where 10=the plants in the best experimental unit in each replication. During the course of the growing season the untreated control in each replicate was labelled as the sentinel plot, and these plots were monitored weekly for visual symptoms of white mold infection on plant parts. Once white mold was detected in the sentinel plots, white mold severity ratings commenced. Each white mold severity rating involved taking 10 visual assessments for each plot. The assessments were made in two rows, 0.5 m in length by visually assessing the percentage of the plot with symptoms of white mold on a scale of 0 (no disease symptoms) to 100 (100% of plot with symptoms of white mold). Mean disease severities were calculated as the mean of the 10 plot ratings within each treatment. The ratings only included environments that had white mold present in the trial at the time of the rating. The earliest rating started 7 d after the first application (DAA1). Once the second foliar fungicide was applied, ratings were based on days after the second application (DAA2).
Percent weed ground cover ratings were completed 21, 35, and 56 DAE. Visual assessments were made by estimating the amount of ground area within each plot that was covered by that particular weed species present. Percent weed ground cover was calculated by adding all weed species together within a plot.
Crop desiccation involved applying diquat at 0.36 kg a.i. ha−1 at 80–90% natural leaf defoliation and at least 80% of pods had turned yellow, to facilitate harvest. Hege 120 and 140 (Wintersteiger Inc. 4705 Amelia Earhart Drive Salt Lake City, UT) combines were used to thresh plots. Pod drop ratings were evaluated immediately after harvest. Pod drop assessments were completed by counting all of the pods with viable seed that had fallen off presumed infected white mold plants. Yield and seed weights were adjusted to 18% moisture, and yield was converted to kilograms per hectare. Seed weight was estimated by measuring the weight (g) of 100 randomly selected whole seed from harvested seed samples.
Net economic returns were determined based on Tharp et al. (2004). Calculations consisted of taking the suggested retail price of the insecticides, herbicides and fungicides plus an average application cost to generate the treatment cost. Average crop insurance claim prices from the 2007 and 2008 (M. Smith, AgriCorp, 2009, personal communication) seasons were used to calculate the average price per kilogram. Gross return was generated by multiplying the average price by the harvested weight. The gross return minus the treatment cost provided the overall net economic return for each treatment.
Net economic return was computed using the formula (1):
Other costs, such as land, tillage, fertilizer, seed, planting, additional pesticides and application, combining and trucking, were not included in the calculation of net economic return, as these costs are assumed to be constant across all treatments.
Analysis of variance was performed on the data, using PROC MIXED (SAS version 9.1, SAS Institute, Inc, Cary, NC). Fixed effects included insecticide, herbicide, and fungicide treatment and their interactions. Random effects included environment (locations, planting date and years), and interactions with environment and fixed effects. The interaction involving environment by insecticide by herbicide by fungicide was used to determine if environments could be combined for analysis. Data were pooled into “groups” when there was no significant environment by insecticide by herbicide by fungicide interaction. To satisfy the assumptions of normality based on the highest Shapiro-Wilk statistic, percent white mold severity at 14 DAA1 and 14 DAA2, and percent weed ground cover at 56 DAE were log transformed; pod drop, harvest weight and net economic return were square root transformed; and percent plant emergence at 1 DAE were arcsine square root transformed. Transformed means were back transformed to their original scale for presentation. Fisher's Protected LSD (P<0.05) was used to separate means.

RESULTS AND DISCUSSION

Variation in weed pressure and white mold severity occurred across environments (Table 1). Weed pressure values consisted of low (<2), medium (2–5) and high (>5) percent weed ground cover. Common weed species included velvetleaf (Abutilon theophrasti), wild mustard (Sinapis arvensis) and barnyard grass (Echinochloa crus-galli) at Plattsville, large crabgrass (Digitaria sanguinalis) at Ridgetown, and common lambsquarters (Chenopodium album), green foxtail (Setaria viridis), common ragweed (Ambrosia artemisiifolia), and redroot pigweed (Amaranthus retroflexus) at all three sites. White mold pressure values consist of none (0), low (<1–5), medium (5–20) and high (>20) percent white mold severity 14 DAA2. Environments with medium to high weed pressure included Plattsville in 2007 and 2008, and Ridgetown in 2007 and 2008. Environments with medium to high white mold pressure included Exeter 2008, Plattsville 2008 and Ridgetown 2008. The environments with medium to high weed and white mold pressure generally resulted in the greatest treatment differences and had a greater chance for interaction between weed and white mold pressure, resulting in higher percent white mold severity due to weed pressure.
Table 1
Table 1 Weed and white mold pressures that occurred in two environments at Exeter (E), Plattsville (P) and Ridgetown (R), ON, in 2007 (7) and 2008 (8)
z
Weed pressure values consist of low=<2, medium=2–5 and high=>5 percent weed ground cover.
y
Common weed species included velvetleaf (Abutilon theophrasti), wild mustard (Sinapis arvensis) and barnyard grass (Echinochloa crus-galli) at Plattsville, large crabgrass (Digitaria sanguinalis) at Ridgetown, and common lambsquarters (Chenopodium album), green foxtail (Setaria viridis), common ragweed (Ambrosia artemisiifolia), and redroot pigweed (Amaranthus retroflexus) at all three sites.
x
White mold pressure values consist of none=0, low=<1–5, medium=5–20 and high=>20 percent white mold severity 14 DAA2.

Emergence and Vigour

Thiamethoxam increased plant emergence in 12% of the environments at 1 d after emergence (DAE), and reduced plant emergence in 25% of the environments (Table 2). The latter effect may have been due to mechanical damage to the seed from leaving it in the seed treater for an excessive period of time. No differences in plant emergence were detected at 7 DAE (data not shown). Thiamethoxam reduced plant vigour in three environments, but two of these environments were suspected to have mechanical seed damage. Twenty-five percent of the environments showed a positive plant vigour response to thiamethoxam (Table 2). This increase may demonstrate plant growth benefits of thiamethoxam. However, this effect was short-lived and was not observed 14 DAE (data not shown). The environments with increased emergence did not correspond exactly with the environments with increased vigour. Therefore, the plant growth benefit of thiamethoxam is inconclusive for plant emergence and plant vigour.
Table 2
Table 2 Means of percent plant emergence 1 d after emergence (DAE) and plant vigour 7 DAE, respectively, of great northern bean (cv. Beryl) treated with insecticide, herbicide and fungicide programs in two environments at Exeter (E), Plattsville (P) and Ridgetown (R), ON, in 2007 (7) and 2008 (8)
z
Percent plant emergence: Group 1 includes E7-1, P7-1 and R7-1. Group 2 includes E7-2, E8-2, P7-2, P8-2, R7-2 and R8-2. Group 3 includes E8-1 and P8-1. Group 4 includes R8-1.
y
Plant vigour: Group 1 includes E7-1 and E7-2. Group 2 includes P7-1 and P7-2. Group 3 includes R7-1, R7-2, R8-1 and R8-2. Group 4 includes E8-1. Group 5 includes E8-2. Group 6 includes P8-1. Group 7 includes P8-2.
x
All two-way and three-way interaction effects of insecticide, herbicide and fungicide were not significant in a F-test in the Proc Mixed procedure of SAS.

a, b Means followed by the same letter within each column and treatment set are not significantly different according to Fisher's protected LSD test (P<0.05).

*, ** Denote significant differences at P<0.05 and P<0.01, respectively.

The economic herbicide program showed an increase in emergence at 1 DAE compared with the premium herbicide program in 25% of environments. Although no phytotoxicity was observed at any location, imazethapyr has been reported to stunt roots in cool wet soils (Sinclair 1993; Mills and Jones 1996), which may explain this result. The premium herbicide program showed a positive plant vigour response compared with the economic herbicide program in 12% of environments. This response cannot be explained. There was no difference in plant emergence and vigour due to the herbicide program 14 DAE (data not shown). The fungicide treatments had no effect on percent plant emergence or plant vigour.

White Mold Severity Rating 1 and 2

A total of eight white mold ratings were completed in the environments where white mold was present to some degree (Table 1). The white mold severity ratings presented in Table 3 were assessed 14 DAA1 for severity rating 1 and at 14 DAA2 for severity rating 2. Severity rating 1 consisted of seven environments, while severity rating 2 consisted of nine environments. Both severity ratings included environments with white mold pressures ranging from low to high. All ratings followed a similar trend.
Table 3
Table 3 Means of white mold severity 14 d after the first application (DAA1) (Severity 1) and 14 d after the second application (DAA2) (Severity 2) of great northern bean (cv. Beryl) treated with insecticide, herbicide and fungicide programs in two environments at Exeter (E), Plattsville (P) and Ridgetown (R), ON, in 2007 (7) and 2008 (8)
z
White mold severity 1: Group 1 includes E7-1, P7-1 and R8-2. Group 2 includes E8-1. Group 3 includes P8-1 and R8-1. Group 4 includes P8-2.
y
White mold severity 2: Group 1 includes E7-1, E8-1 and E 8-2. Group 2 includes P7-1 and P7-2. Group 3 includes P8-1. Group 4 includes P8-2. Group 5 includes R8-1 and R8-2
x
All two-way and three-way interaction effects of insecticide, herbicide and fungicide were not significant in a F-test in the Proc Mixed procedure of SAS.

a, b Means followed by the same letter within each column and treatment set are not significantly different according to Fisher's protected LSD test (P<0.05).

*, ** Denote significant differences at P<0.05 and P<0.01, respectively.

Plants treated with thiamethoxam had higher white mold severity (Table 3) at one environment for the first disease rating at 14 DAA1. This site had higher plant vigour, which may have led to an increase in the plant canopy density resulting in higher white mold severity. No other effect of thiamethoxam on white mold severity was detected.
Compared with the premium herbicide program, the economic herbicide program had increased white mold severity in 29% of the environments for severity rating 1, and 22% of the environments for severity rating 2, when considering the environments with medium to high disease pressure only. The economic herbicide program consistently had increased percent weed ground cover (Table 4), and this may have influenced the plot microclimate, resulting in an environment more conducive to white mold development. This agrees with other studies (Blackshaw et al. 2000). An increase in weed pressure can reduce air flow between plants, limit light penetration, and trap moisture in the plant canopy (Burnside et al. 1998). As well, weeds infected with white mold can bridge the infection to dry bean plants in close contact with them (Dillard and Hunter 1986). These microclimatic conditions were particularly evident in environments with high white mold pressure.
Table 4
Table 4 Means of percent weed ground cover 56 d after planting (DAP) of great northern bean (cv. Beryl) treated with insecticide, herbicide and fungicide programs in two environments at Exeter (E), Plattsville (P) and Ridgetown (R), ON, in 2007 (7) and 2008 (8)
z
Percent weed ground cover: Group1 includes E7-2, P7-2, R7-2, P8-2 and R8-2. Group 2 includes E7-1, 8-1 and P7-1. Group 3 includes R7-1. Group 4 includes P8-1. Group 5 includes R8-1
y
All two-way and three-way interaction effects of insecticide, herbicide and fungicide were not significant in a F-test in the Proc Mixed procedure of SAS.
x
Common weed species included velvetleaf (Abutilon theophrasti), wild mustard (Sinapis arvensis) and barnyard grass (Echinochloa crus-galli) at Plattsville, large crabgrass (Digitaria sanguinalis) at Ridgetown, and common lambsquarters (Chenopodium album), green foxtail (Setaria viridis), common ragweed (Ambrosia artemisiifolia), and redroot pigweed (Amaranthus retroflexus) at all three sites.

a, b Means followed by the same letter within each column and treatment set are not significantly different according to Fisher's protected LSD test (P<0.05).

*, ** Denote significant differences at P<0.05 and P<0.01, respectively.

Foliar fungicides reduced white mold severity in 57 and 100% of the environments for severity ratings 1 and 2, respectively. Fluazinam provided better control of white mold than boscalid in 14 and 78% of all environments for white mold severity ratings 1 and 2, respectively. Fluazinam provided better control of white mold than cyprodinil/fludioxonil in 33% of all environments for white mold severity rating 2. This suggests that fungicides are necessary for disease control under various white mold severities, and that fluazinam provided the best control followed by cyprodinil/ fludioxonil, followed by boscalid.

Percent Weed Ground Cover

Thiamethoxam reduced the percent weed ground cover in the same environment where it increased crop emergence, suggesting that increasing plant populations reduced percent weed ground cover. Blackshaw et al. (2000) concluded that higher bean populations along with the use of herbicides led to decreased weed pressure and increased yields. There was no effect of thiamethoxam on weed ground cover at the other sites. The premium herbicide program decreased weed ground cover relative to the economic program in all environments. The premium program consisted of s-metolachlor plus imazethapyr, which provided improved control of the weed species in this study, compared with trifluralin. The fungicide treatments had no effect on percent weed ground cover. Percent weed ground cover ratings evaluated 21 and 35 days after planting show similar trends as 56 days after planting (data not shown).

Pod Drop

Pod drop ratings only included environments that had white mold present (Table 5). Thiamethoxam reduced pod drop in 11% of the environments. This environment is different than the one described earlier, where thiamethoxam provided higher plant emergence and lower weed ground cover. Therefore, thiamethoxam's impact on pod drop cannot be attributed to any benefit measured earlier in the season. In the same environment, pod drop was reduced with the use of a premium herbicide program. This environment had high weed pressure. Compared with the economic herbicide program, the premium herbicide reduced weed pressure, which resulted in a decrease in white mold severity and this led to a decrease in pod drop. Fungicides reduced pod drop in 22% of environments that had medium to high disease severities. These data suggest that fungicides helped to reduce pod drop by controlling white mold severity, thereby eliminating some of the associated losses from white mold. An interaction between insecticide and fungicide for pod drop occurred in 55% of environments. The results suggest that the thiamethoxam treatments where boscalid was applied had increased pod drop. Also, thiamethoxam treatments combined with fluazinam or cyprodinil/fludioxonil fungicides gave lower pod drop ratings compared with the untreated fungicide control. No explanation can be given for either interaction because there is no consistent trend.
Table 5
Table 5 Means of pod drop immediately after harvest and 100 seed weight (g) after harvest of great northern bean (cv. Beryl) treated with insecticide, herbicide and fungicide programs in two environments at Exeter (E), Plattsville (P) and Ridgetown (R), ON, in 2007 (7) and 2008 (8)
z
Pod Drop: Group 1 includes E7-1, P7-1, E8-1, P8-1 and R8-1. Group 2 includes E7-2 and P7-2. Group 3 includes E8-2. Group 4 includes R8-2.
y
100 seed weight: Group 1 includes E7-1, E7-2, E8-1 and E8-2. Group 2 includes P7-1 and P8-1. Group 3 includes P7-2 and P8-2. Group 4 includes R7-1. Group 5 includes R7-2 and R8-1. Group 6 includes R8-2.
x
All two-way and three-way interaction effects of insecticide, herbicide and fungicide were not significant in a F-test in the Proc Mixed procedure of SAS, except for the interaction of insecticide×fungicide for group 1 for pod drop, and the interaction of insecticide×herbicide for group 6 for 100-seed weight. In the former, thiamethoxam had higher pod drop than the untreated seed, for the boscalid fungicide treatment. In addition, thiamethoxam combined with fluazinam or cyprodinil/fludioxonil had lower pod drop than the untreated fungicide control. In the latter, thiamethoxam had higher seed weight than the untreated seed for both herbicide programs, and the premium herbicide program had higher seed weight than the economic program, for the untreated seed treatment.

a, b Means followed by the same letter within each column and treatment set are not significantly different according to Fisher's protected LSD test (P<0.05).

*, ** Denote significant differences at P<0.05 and P<0.01, respectively.

100-seed Weight

There was no effect of thiamethoxam on seed weight (Table 5). The premium herbicide program increased seed weight over the economic herbicide program in one environment. In this environment there was high weed pressure (Table 4), and the premium herbicide program reduced percent weed ground cover compared with the economic program, resulting in larger seeds. Fungicide use increased seed weight compared with the untreated control in 50% of all environments, which agrees with other work (del Rio et al. 2004). All of these environments had medium to high white mold severity. An interaction between insecticide and herbicide occurred for seed weight in one environment. This interaction showed that thiamethoxam increased seed weight for both herbicide programs, but the premium herbicide program increased seed weight over the economic program only when no insecticide was applied. This suggests that the premium herbicide did not increase seed weight when combined with thiamethoxam, and the benefits of premium herbicide and thiamethoxam were not additive for seed weight.

Harvested Weight

Thiamethoxam increased harvested weight in 25% of the environments (Table 6), but only one of these environments was linked to increased plant emergence and reduced weed pressure when thiamethoxam was applied, which provides only a partial explanation for the increased harvested weight. However, thiamethoxam also reduced harvested weight in 25% of the environments. This effect may be partially explained by the fact that two of three of these environments had reduced plant emergence from mechanical seed damage. Harvest weights increased when using the premium herbicide program over the economic in 67% of all environments. This occurred in environments with medium to high weed pressure. These data suggest that effectively controlling weeds resulted in higher harvested weight (Malik et al. 1993; Chikoye et al. 1995; Sikkema et al. 2007). The economic herbicide program had higher harvested weights in one environment. In this environment there were few weeds in either treatment, so any potential benefits of the premium herbicide program were not evident. It is also possible that imazethapyr caused crop injury in the premium herbicide treatments, resulting in reduced harvest weight. Fungicides increased harvested weight in 58% of all environments. Each of these environments had medium to high white mold pressure, and had the greatest reduction in white mold severity when a fungicide was applied. In 57% of these environments, fluazinam increased harvested weights compared with cyprodinil/fludioxonil and boscalid. The remaining environments had little to no white mold, and did not respond to fungicide application.
Table 6
Table 6 Means of harvest weight (kg ha−1) of great northern bean (cv. Beryl) treated with insecticide, herbicide and fungicide programs in two environments at Exeter (E), Plattsville (P) and Ridgetown (R), ON, in 2007 (7) and 2008 (8)z
z
Harvested weight: Group 1 includes E7-1, E7-2 and P7-2. Group 2 includes P7-1, E8-1, P8-1 and P8-2. Group 3 includes R7-1. Group 4 includes R7-2. Group 5 includes E8-2. Group 6 includes R8-1. Group 7 includes R8-2.
y
All two-way and three-way interaction effects of insecticide, herbicide and fungicide were not significant in a F-test in the Proc-Mixed procedure in SAS.

a, b Means followed by the same letter within each column and treatment set are not significantly different according to Fisher's protected LSD test ( P<0.05).

*, ** Denote significant differences at P<0.05 and P<0.01, respectively.

The advantage to using the premium versus the economic herbicide program to reduce white mold severity occurred in up to 29% of environments infected with white mold (Table 3). In these environments, the premium herbicide program also had higher harvested weight. Percent weed ground cover ratings showed an advantage to the premium herbicide program over the economical herbicide program in all environments for percent weed ground cover (Table 4). Two-thirds of these environments had an increase in harvested weight. It is hard to distinguish which factor – weed pressure, white mold alone, or a combination of these factors – had the greatest effect on harvested weight. High weed pressure provided the most consistent reduction in harvested weight. The environments with reduced white mold severity in the premium herbicide program were not consistent with the environments where there were differences in harvested weight due to weed pressure and white mold. For this reason, it is hard to quantify the interaction of white mold and weeds on harvested weight.

Net Economic Return

Thiamethoxam increased net economic return in 17% of the environments (Table 7). This increase correlates with the increased harvested weight in the same environments. Thiamethoxam reduced net economic returns in 33% of all environments; some of these environments had a reduction in harvested weight. The remaining environments that had reduced net economic returns with thiamethoxam-treated seed were due to the cost of thiamethoxam because the harvested weights were similar. The premium herbicide program improved net economic returns in 33% of all environments. These environments had high weed pressures. No economic benefit was observed in the rest of the environments, but five of the remaining eight environments had differences in harvested weight. This suggests that weed pressure was high enough to see benefits to the herbicide programs, but differences in cost between the herbicide programs offset the yield advantage.
Table 7
Table 7 Means of net economic return ($ ha−1) of great northern bean (cv. Beryl) treated with insecticide, herbicide and fungicide programs in two environments at Exeter (E), Plattsville (P) and Ridgetown (R), ON, in 2007 (7) and 2008 (8)
z
Net economic return: Group 1 includes E7-1 and E7-2 and E8-1 and E8-2. Group 2 includes P7-1 and P7-2, P8-1 and P8-2. Group 3 includes R7-1. Group 4 includes R7-2. Group 5 includes R8-1. Group 6 includes R8-2.
y
All two-way and three-way interaction effects of insecticide, herbicide and fungicide were not significant in a F-test in the Proc Mixed procedure of SAS.

a–c Means followed by the same letter within each column and treatment set are not significantly different according to Fisher's protected LSD test (P<0.05).

*, ** Denote significant differences at P<0.05 and P<0.01, respectively.

Foliar fungicides improved net economic return in 33% of the environments. These environments consistently had medium to high white mold pressures. These disease conditions were necessary to realize a net economic return from using fungicides. Fluazinam provided the greatest increase in net returns, followed by cyprodinil/ fludioxonil and boscalid. Foliar fungicides had no effect on net economic return in 67% of all environments. In 42% of these environments, white mold pressure was low. In the remaining 25% of these environments, white mold pressure was moderate, but any benefits of fungicide application were offset by the cost of the fungicide and application. In these environments, it is possible that a single fungicide application may have provided a positive economic return. Any interaction between weed pressure and white mold severity did not translate into differences in net economic return. In the environments with a weed and white mold interaction, the advantages were offset by the increase in cost of the premium herbicide program.
In summary, thiamethoxam increased plant emergence, plant vigour, harvested weight, 100-seed weight and net economic return in at least some environments. There was little consistency between ratings as to which environments showed a positive effect to thiamethoxam. In at least two environments, thiamethoxam-treated plants also had reduced plant emergence, plant vigour, harvested weight and net economic returns, but this may have been due to mechanical seed damage. No explanation can be given for the remaining environments. Overall, the data suggest that the plant growth benefits of thiamethoxam are unclear and hard to quantify.
Compared with the economic herbicide program, the premium herbicide program reduced weed ground cover, increased harvested weights in medium to high weed environments and increased net economic returns in high weed environments. The economic herbicide program resulted in higher weed populations that may have influenced the plot microclimate resulting in an environment that was more favourable to white mold development. There was higher white mold severity in 22% of the environments with the economic herbicide program. White mold severity was increased by 2 to 10% under high weed pressure, which resulted in reduced harvested weight, but did not impact the net economic return.
Under medium to high disease pressure, fungicides reduced white mold severity and increased harvest weight in at least 80% of the environments, increased net economic returns in 50% of environments and increased 100 seed weight in 80% of environments. Compared with cyprodinil/fludioxonil and boscalid, fluazinam reduced white mold severity and increased harvested weight and net economic returns at 50% of sites where differences between the fungicide and control treatments were documented.
The pest management program that provided the greatest benefits in sites with medium to high weed pressures and medium to high white mold pressures was thiamethoxam-treated seeds, with the premium herbicide program and fluazinam fungicide.

ACKNOWLEDGEMENTS

The authors acknowledge the technical support of D. Bilyea, T. Cowan, D. Depuydt, C. Shropshire and S. Willis. In addition, assistance was received from C. Shropshire with the statistical analysis, Dr. R. Vyn with the economic analysis, Dr. G. Boland with disease management, and Dr. N. Soltani with final editing of the manuscript for publication. The authors also acknowledge funding support from the Ontario Bean Producers Marketing Board and the Ontario Coloured Bean Growers Association.

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Information & Authors

Information

Published In

cover image Canadian Journal of Plant Science
Canadian Journal of Plant Science
Volume 91Number 3May 2011
Pages: 587 - 598

History

Received: 7 June 2010
Version of record online: 1 January 2011
Accepted: 4 January 2011

Key Words

  1. Dry bean (Phaseolus vulgaris)
  2. economics
  3. imazethepyr
  4. s-metolachlor
  5. white mold (Sclerotinia sclerotiorum)
  6. thiamethoxam
  7. trifluralin
  8. weeds

Mots clés

  1. Haricot sec (Phaseolus vulgaris)
  2. économique
  3. imazéthapyr
  4. s-métolachlor
  5. moisissure blanche (Sclerotinia sclerotiorum)
  6. thiaméthoxame
  7. trifluralin
  8. mauvaises herbes

Authors

Affiliations

Gerard Pynenburg
Department of Plant Agriculture, University of Guelph Ridgetown Campus, Ridgetown, Ontario, Canada N0P 2C0
Peter Sikkema
Department of Plant Agriculture, University of Guelph Ridgetown Campus, Ridgetown, Ontario, Canada N0P 2C0
Darren Robinson
Department of Plant Agriculture, University of Guelph Ridgetown Campus, Ridgetown, Ontario, Canada N0P 2C0
Chris Gillard
Department of Plant Agriculture, University of Guelph Ridgetown Campus, Ridgetown, Ontario, Canada N0P 2C0

Notes

Abbreviations: DAA1, days after first application; DAA2, days after second application; DAE, days after emergence

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