© 2010 Plant Management Network.
Effects of Foliar Fungicide and Insecticide Applications on Soybean in Ohio
A. E. Dorrance, C. Cruz, D. Mills, Department of Plant Pathology, The Ohio State University, OARDC, Wooster, OH 44691; R. Bender, M. Koenig, G. LaBarge, R. Leeds, D. Mangione, G. McCluer, S. Ruhl, H. Siegrist, A. Sundermeier, D. Sonnenberg, J. Yost, H. Watters, G. Wilson, County Extension Educators, The Ohio State University, Columbus, OH 43210; and R. B. Hammond, Department of Entomology, The Ohio State University, OARDC, Wooster, OH 44691
Dorrance, A. E., Cruz, C., Mills, D., Bender, R., Koenig, M., LaBarge, G., Leeds, R., Mangione, D., McCluer, G., Ruhl, S., Siegrist, H., Sundermeier, A., Sonnenberg, D., Yost, J., Watters, H., Wilson, G., and Hammond, R. B. 2010. Effect of foliar fungicide and insecticide applications on soybeans in Ohio. Online. Plant Health Progress doi:10.1094/PHP-2010-0122-01-RS.
Mid-season applications of Quadris with and without Warrior insecticide were evaluated in 2004 and 2005, and Headline, Folicur, Domark, or Headline plus Folicur were evaluated in 2006, 2007, and 2008 in 37 farm scale studies in Ohio. Producer cooperators selected fields, applied treatments at growth stage R3 and harvested fields. Each trial was rated at growth stage R5 or R6 for incidence and severity of brown spot and frogeye leaf spot. Aphids and foliar disease incidence was low in 2004. Soybean aphids were counted at stage R5 in 2005. Brown spot severity was reduced significantly by Headline in seven of the 13 locations. In the absence of soybean aphid, a single application of fungicide(s) increased yield significantly in only six of the 28 locations, of which only three had yield increases greater than 4.2 bu/acre. Populations of soybean aphids were high during 2005 at nine locations, and an insecticide application increased yield significantly at eight locations. These data indicated that foliar diseases and aphids contribute to yield loss in soybeans. However, more studies are required to determine action thresholds for brown spot and frogeye leaf spot.
Foliar fungicide applications have been promoted by industry in Ohio for corn, soybean and wheat in the past 6 years. Part of this push came as a result of preparations for soybean rust, caused by Phakopsora pachyrhizi, a new invasive foliar pathogen, as well as presumed "plant health benefits." Additionally, since 2000, various insecticides have been used due to the recent arrival of the soybean aphid (Aphid glycines) (7,10)
Swoboda and Pederson (9) reported that there was no significant increase in yield in Iowa when Headline or Folicur were applied alone or in combination at R1, R3, or R5 growth stages on soybean. In addition, Hershman et al. (3) reported that Quadris applied alone to soybean did not significantly increase yield but the combination of Quadris plus Warrior did increase yield by an average of 4.2 bu/acre during 2003 in Kentucky. In contrast, Sikora et al. (8) reported that two successive fungicide applications to soybean may now be required in Alabama to effectively manage soybean rust in addition to several other late season foliar and stem diseases.
Currently, the most common foliar disease of soybean in Ohio is brown spot caused by Septoria glycines and the yield impact from this lower canopy pathogen can range from 3 to 6 bu/acre (1). Interestingly, for the first time frogeye leaf spot (Cercospora sojina) was a serious pathogen on highly susceptible varieties in Ohio during 2006 and 2007 (2). The objective of the current study was to evaluate the effects of foliar fungicides with and without an insecticide on soybean foliar diseases, soybean aphids, and yield in large scale on-farm trials in Ohio.
These studies consisted of on-farm trials with only three to four treatments and three to five replications per location in fields which ranged in size from 50 to 250 acres. Each year, producers selected the field and cultivar, applied treatments, and harvested plots. All applications were made at R3, when pods were 5 mm long at one of the four uppermost nodes with a fully expanded trifoliate leaf (5). Soybeans in each study were evaluated for percent leaf area affected by brown spot in the lower and mid canopy and frogeye leaf spot in the upper canopy at growth stage R5 or R6 when seeds were 3 mm long in a pod to full seed at one of the four uppermost nodes with fully expanded trifoliate leaves. For both foliar diseases, a minimum of four observations were made in each plot and these were selected randomly, but special attention was given to include locations where the canopy was most dense. The mean number of aphids per plant was recorded for five plants at each of four locations per plot at growth stage R5 or R6.
Data collected at each location was analyzed separately due to differences in cultivars, locations, and pressure exerted by soybean aphids and diseases. The means from each plot for percent leaf area affected by disease, number of aphids per plant, and yield were analyzed with PROC GLM of SAS (SAS Institute Inc., Cary, NC).
Quadris, Warrior, Quadris plus Warrior 2004 and 2005
Quadris (6.4 fl oz/acre), Warrior (3.2 fl oz/acre), and Quadris (6.4 fl oz) plus Warrior (3.2 fl oz/acre) were evaluated at 10 and 14 locations during 2004 and 2005, respectively. The planting dates ranged from April 16 to June 1. Fungicide and insecticide applications were made using 12 to 20 gpa and 30 to 70 psi. A preliminary report of results at 10 locations during 2004 was published earlier (4) (Table 1). Brown spot was present at very low levels and limited to the lower canopy during 2004 and there were no soybean aphids or frogeye leaf spot. During 2005, the mean for brown spot severity in non-treated plots ranged from 2.0 to 42.5% of leaf area affected in the lower to mid canopy in eight of 14 locations and frogeye leaf spot was absent (Table 2 and Table 3). In addition, nine of the 14 locations had a high incidence of soybean aphid which ranged from a mean of 181 aphids per plant in Shel-J to 3333 aphids per plant in non-treated plots at the Ott location (Table 2). Yields were not significantly different for treatments in eight of the 10 locations in 2004 (4) (Table 1). At the Hardin location, yields for all treatments were significantly higher than the non-treated while at the Wood location, only Quadris and Quadris plus Warrior had significantly higher yields. During 2005, yields of Quadris alone were significantly higher than the non-treated in three of the nine locations with soybean aphids and only one (Licking) of the five locations without aphids. Yields with Warrior and Quadris plus Warrior were significantly higher than the non-treated in eight of the nine locations with soybean aphids (Table 2). Warrior increased yield significantly in two of the five locations without aphids and Quadris plus Warrior increased yield in three of those locations (Table 3). Interestingly, yields from Warrior alone and Warrior plus Quadris were not significantly different in any of the 14 trials in 2005 (Table 2). Thus, the addition of a fungicide did not improve the yield response to insecticide.
Table 1. Mean yields (bu/acre) of soybeans following applications of Quadris (6.4 fl oz/acre), Warrior (3.2 fl oz/acre) and Quadris (6.4) plus Warrior (3.2 fl oz/acre) at growth stage R3 at locations in Ohio during 2004.
Table 2. Mean number of aphids per plant, percent leaf area affected by brown spot in the mid canopy, and yield of soybean non-treated and treated at growth stage R3 with Quadris (6.4 fl oz/acre), Warrior (3.2 fl oz/acre), or Quadris (6.4 fl oz/acre) plus Warrior (3.2 fl oz/acre) in Ohio during 2005 at locations with aphids.
Table 3. Mean percent leaf area affected by brown spot in the mid canopy, and yield (bu/acre) of soybean non-treated and treated at R3 growth stage with Quadris (6.4 fl oz/acre), Warrior (3.2 fl oz/acre), or Quadris (6.4 fl oz/acre) plus Warrior (3.2 fl oz/acre) in Ohio during 2005 at locations without aphids.
Headline, Folicur, Headline plus Folicur 2006
Due to the extensive yield loss where soybean aphids were present, trials after 2005 did not evaluate insecticide applications. Foliar applications of Headline (6 fl oz/acre), Folicur (4 fl oz/acre) and Headline (6 fl oz/acre) plus Folicur (4 fl oz/acre) were evaluated at six locations (Table 4). Fungicide applications were made using 15 to 25 gpa and 45 to 80 psi. Seasonal rainfall varied from 21.3 to 29.5 inches. During 2006, brown spot levels were less than 5% leaf area affected in five of the six trials. At the Fayette location where brown spot levels averaged 27.4% of leaf area affected in non-treated plots, Headline and Headline plus Folicur significantly reduced brown spot rated at growth stage R5 (Table 4). Yields from fungicide treatments were higher than non-treated in only two of the six locations: Headline plus Folicur at Fayette (P = 0.0567) and Headline alone and Headline plus Folicur at the Shelby location (P = 0.0492).
Table 4. Mean percent leaf area affected by brown spot (BS) or frogeye leaf spot (FLS) and yield following fungicide applications of Headline (6 fl oz/acre), Folicur (4 fl oz/acre), or Headline (6 fl oz) plus Folicur (4 fl oz/acre) at R3 growth stage in Ohio during 2006.w
w Soybean pods at growth stage R3 were 5 mm long at one of four uppermost, mainstem nodes.
x Seeds were 3 mm long in a pod at one of the four uppermost nodes with a fully expanded trifoliate leaf at growth stage R5; "−" indicates that brown spot disease in the mid canopy was below 1% of leaf area.
y Means were separated by Fisher’s protected least significant difference (LSD) at P ≤ 0.05 and NS indicates not significant.
z Yields adjusted to 13% moisture.
Headline or Domark, 2007 and 2008
Headline and Domark were evaluated at four locations in 2007 and 2008. Applications were made using 20 gpa in 2007 and 15 to 20 gpa in 2008 with pressures at 60 to 75 psi in both years. Seasonal rainfall varied from 14.0 to 17.6 inches in 2007 and 19.3 to 23.4 inches in 2008. The Mercer Co. location in 2008 was not included in the final analysis due to flooding and a high incidence of Phytophthora stem rot caused by Phytophthora sojae. Across the remaining seven locations, the percent of leaf area affected by brown spot in non-treated plots averaged from 6.9 to 13.6% at growth stage R6 (Table 5). Headline or Domark alone significantly reduced the level of brown spot at six locations. Yields were not significantly different across treatments for three of the four locations during 2007 (Table 5). At the Wood location, Headline resulted in significantly higher yields than non-treated plots; however, one of the non-treated controls was 9 bu/acre lower than the field mean. Without that replication of the control, yields were not significantly different (analysis not shown). During 2008, yields were significantly different across treatments with the non-treated significantly higher than Headline or Domark in Delaware, Domark was significantly higher than the non-treated at Hardin, and Headline was significantly higher than the non-treated and Domark at the Ross location (Table 5).
Table 5. Mean percent leaf area affected by brown spot at soybean growth stage R6 following fungicide applications of Headline (6 fl oz/acre), or Domark (4 fl oz/acre) at growth stage R3 in Ohio during 2007 and 2008x.
x Soybean pods at growth stage R3 were 5 mm long at one of four uppermost, mainstem nodes and at R6 seeds filled the pod cavity at one of these nodes.
y Means were separated by Fisher’s protected least significant difference (LSD) at P ≤ 0.05 and NS indicates not significantly different.
z Yields adjusted to 13% moisture.
When present in high numbers, soybean aphids significantly reduced yields and Warrior provided excellent control. Application of fungicides reduced the incidence and severity of brown spot and frogeye leaf spot in Ohio. In trials without aphid pressure, there was a significant increase in yield at six out of 28 locations following application of Quadris or Headline but only three had yield increases greater than 4.2 bu/acre. The economic threshold for application of fungicides and insecticides can vary quite widely as the price per bushel fluctuates between and within years. Soybean sold at $7/bu represented the "break-even" price when fungicide and application costs total $28/acre. The results of large on-farm trials were similar to results from smaller plots on research farms (9). These data supported previous studies which indicated insecticide application was economical when soybean aphids reach damaging levels in fields (6). More studies are needed to determine the specific action thresholds for brown spot and frogeye leaf spot at various growth stages of soybean and the environmental conditions necessary for continuation of disease development.
We wish to thank the numerous producers and chemical dealers that collaborated on this project. This project was funded by State and Federal Funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University, The Ohio State University Extension, and county commissioners to extension for Delaware, Fayette, Fulton, Hancock, Hardin, Henry, Licking, Mercer, Miami, Morrow, Ottawa, Ross, Shelby, and Wood counties. Funding was also provided in part through soybean check off dollars from Ohio Soybean Council, Top Farmer Club of Ohio, and Ohio Seed Improvement Association. We would also like to thank Syngenta Crop Protection, BASF, and Valent for providing products.
1. Cruz, C. 2008. Impact of foliar diseases on soybeans in Ohio: Frogeye leaf spot and Septoria Brown Spot. M.S. thesis, The Ohio State Univ., Columbus, OH
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10. Venette, R. C., and Ragsdale, D. W. 2004. Assessing the invasion by soybean aphid (Homoptera: Aphididae): Where will it end? Ann. Entomol. Soc. Am. 97:219-226.