Considering Foliar Fungicides for Corn in 2009?

A Look at the Results of University Trials in Wisconsin and the North Central Region

Paul Esker and Joe Lauer

Extension Plant Pathologist and Extension Corn Agronomist

We continue to receive questions regarding the cost-effective use of foliar fungicides in corn. Continuing with the previous two articles in the Wisconsin Crop Manager that focused on results from on-farm foliar fungicide trials for corn grain and corn silage, in this article, we would like to address some of the questions that have been raised over the past winter meeting season regarding the use of foliar fungicides for corn. These questions have been about the perceived need for foliar fungicides, field plot layout and design, the number of observations (i.e., sample size), the question of an increase in yield in the absence of disease (i.e., plant health), and the role of IPM for corn disease management. All of these questions have relevance and need to be addressed, as well as misconceptions regarding the data coming from our small plot trials, in particular. 

One question that has been discussed over the winter meeting season has been the role of “open” versus “closed” plots and whether these create unique microenvironments. Likewise, there continues to be questions about small plots versus long strip trials and whether small plot data are meaningful at the farm scale. In all of our trials, except Hancock, alleyways measured two to four feet between replicate blocks. It is unlikely that alleys of this size cause failure of foliar fungicide treatments. At Hancock, we did have 10 foot alleyways between replicate blocks; however, our plot dimensions were 8 rows wide and 50 feet long (approximately double the size of corn efficacy trial plots). Also, we did not note any difference in the level (severity) of corn diseases when scouting in these plots, whether in the middle of the plot or at the end. 

A Look at Trial Results.

In 2008, the Field Crops Plant Pathology program conducted foliar fungicide trials at multiple locations (not including the on-farm trials around the state), including, Arlington, Hancock, and Lancaster. These studies included general efficacy trials as well as trials focused on the effect of previous crop history and fungicide timing on corn disease development and yield (Esker et al. 2009). The UW Corn Agronomy group has conducted research related to corn response to foliar fungicides and a summary of the 2008 trials are available in the “Gold Book” at http://corn.agronomy.wisc.edu/Research/Default.aspx One study that was conducted in 2008 and 2007 was a foliar fungicide trial in a corn-soybean-wheat long term rotation block that examined the effect of corn hybrid and fungicide on corn yield.

            Field Crops Plant Pathology Efficacy Trials. In our trials conducted at Arlington and Lancaster, the hybrid Pioneer 37Y14 was used. This hybrid has the following disease ratings (1 = poor; 9 = outstanding): northern corn leaf blight (6), anthracnose stalk rot (4), Gibberella ear rot (5), eyespot (6), and common rust (4). Plots measured 4 rows by 50 feet long and were planted at a density of 33,000 plants per acre.  

At Lancaster, yield ranged from 124 bushels per acre (Quilt) to 157 bushels per acre (Evito at 2 ounces per acre), but there was no evidence of differences among the treatments (P = 0.88) (Lauer 2002). Furthermore, there was no evidence of an effect of foliar fungicide on either grain moisture (P = 0.58) (Range: 18.6 to 19.8%) or test weight (P =0.86) (Range: 56.5 to 57.2 pounds per bushel). In Figure 1, raw data are shown using a stripchart; plot yields were quite variable and centered around the mean yield for the trial of 135 bu/a. Disease severity prior to fungicide application was low (< 1%, common rust); post-application, there was no evidence of any differences in disease severity for common rust, eyespot, anthracnose leaf blight, or incidence of stalk rot (based on a push test).

Figure 1. Stripchart showing all raw data, by replicate and treatment, for corn foliar fungicide efficacy trials conducted at the Lancaster ARS (Lancaster, WI). Each symbol represents the plot yield for each plot. The mean yield for the trial was 135 bu/a and is shown by the hortizontal line. All compounds were applied at R1 at their recommended or desired rate for the study.

At Arlington, results were similar to Lancaster in that there was no evidence of an effect of treatment, as mean yield ranged from 176 (experimental) to 194 (Evito at 3 ounces per acre) (P = 0.90), grain moisture (P = 0.63) (Range: 22.3 to 23.6%), and test weight (P = 0.50) (Range: 52.2 to 55.9 pounds per bushel). In Figure 2, raw data are shown using a stripchart; plot yields were quite variable and centered around the mean yield for the trial of 185 bu/a. Disease severity prior to fungicide application was low (< 1%, common rust); post-application, there was no evidence any treatment differences for disease severity of common rust, eyespot, anthracnose leaf blight, or the incidence of stalk rot (based on push test). Incidence of stalk rot at Arlington was lower than at Lancaster.

Role of Previous Crop History and Foliar Fungicides. Based on results from the regional trials in 2007, another study was established in 2008 at the Arlington and Hancock ARS to examine the effect of previous crop history and fungicide application timing on disease development and yield. In these trials, the previous crop at Arlington was either corn or soybean, while at Hancock, the previous crop was either corn or potato. The fungicide treatments were: (i) untreated check, (ii) Stratego at 10 ounces per acre at V12, (iii) Stratego at 10 ounces per acre at VT-R1, and (iv) Stratego at 10 ounces per acre at R2. Corn hybrids were DeKalb (DKC) 57-79 at Arlington and DKC46-28 at Hancock, both planted to 33,000 per acre (Table 1). Overall disease severity was low throughout this study (< 1% severity of common rust on the ear leaf). A summary of the yield results is presented in Table 2. There was no evidence of an effect of foliar fungicides on corn yield at either location. We hypothesize that the lower yields in our previous crop soybean at Arlington were in part due to nitrogen loss from the early season flooding rains.

Table 1. Disease ratings for DKC57-79, DKC46-28, and DKC54-49 for foliar fungal diseases that were observed in Wisconsin in 2008.^Z

Hybrid	NCLBY	GLS	Eyespot	Common rust	ALB	ASR
DKC57-79	3X	6	3	4	3	3
DKC46-28	3	5	2	3	3	5
DKC54-49	3	5	3	4	3	6

^ZDKC57-79 and DKC46-28 were used in previous crop-foliar fungicide trials at Arlington and Hancock, WI, respectively, while DKC57-79 and DKC54-49 were used in the corn/soybean/wheat long term rotation study at Arlington, WI.

^YNCLB = Northern corn leaf blight; GLS = gray leaf spot; ALB = anthracnose leaf blight; ASR = anthracnose stalk rot.

Corn/Soybean/Wheat Rotation Study – Foliar Fungicides for Corn. This trial was conducted at Arlington in long-term rotation plots. A preliminary study was conducted on one hybrid in 2007. The treatments were rotation (corn-corn, corn-soybean, corn-soybean-wheat, corn-wheat-soybean), hybrid (DKC57-79 and DKC54-49 (Table 1)), and fungicide (untreated check, Headline, Quadris, and Quilt). One of the objectives of interest was to determine if differences in anthracnose stalk rot rating may affect the yield response, as DKC57-79 has a “very good” stalk rot rating, while DKC54-49 “good to fair” rating. Plots measured 10 feet by 60 feet. Fungicide applications were made at VT. 

Figure 3. Corn yield response to fungicide application in 2008 at Arlington, WI, stratified by fungicide treatment and rotation.

Some key points from these results include that in the top ten grower returns, there were none from a corn-following-corn rotation and that each fungicide treatment was observed at least two times. In the bottom ten grower returns, eight of those ten were from corn-following-corn rotations and, except for Quadris, the other two fungicide treatments were observed three times.

In all of the top ten returns, yield was greater than 200 bu/a (mean yield = 214 bu/a), while in the bottom ten returns, yield never was above 200 bu/a (mean yield = 183 bu/a). These results indicate that predicting when a foliar fungicide will be cost-effective is difficult. Consideration of additional factors like rotation and genetics is a must for understanding how to improve corn yield.

          Regional University Trials. Similar to the 2007 growing season, Extension Plant Pathologists provided data for a regional summary on foliar fungicides of corn. Compiled by Greg Shaner, Purdue University, there were 68 trials compiled from 13 states and Ontario (Shaner 2008). Specifically, the results of these combined trials illustrated the efficacy of a foliar fungicide for disease control. In the 2008 trials, a mean yield response of greater than 8 bushels per acre was observed in trials where the untreated check had at least a disease severity greater than 5% on the ear leaf in late season assessments. This may provide a  potential threshold for considering the application of a foliar fungicide, however, further research is necessary. As such, this is not the current recommended disease severity threshold for making a foliar fungicide application. Also, it should be noted that the number of comparisons (i.e., the number of trials comparing the untreated check with the foliar fungicide treatment) where this response was observed was only 34% of the comparisons. In the majority of trials, there was no need for a foliar fungicide application. To examine the results from the regional summary, please check here.

Overall – Looking Ahead to 2009.

To date, we have conducted research on foliar fungicides for corn grain and corn silage, and using both small plot and large strip methods. Results from our foliar fungicide trials have not shown a consistent benefit from using foliar fungicides. We will continue to conduct both our small plot (University trials and on-farm) and large strip (on-farm) foliar fungicide trials in 2009 as it helps to improve our ability to make the most appropriate management recommendations for producers.

Corn production is a combination of factors that begins with hybrid selection. Furthermore, there has been a tremendous amount of research to understand how factors like date of planting, pest control (insect, weed, disease), plant density, rotation, soil fertility, harvest timing, tillage, and row spacing all affect corn yield. In terms of foliar fungicides, in the trials where disease severity has been higher (> 5% on the ear leaf), response has been higher; however, the vast majority of trials across the Corn Belt have had disease severity less than 5%. With foliar fungicide prices in the $25-30/a range for 2009 (product cost plus application cost) and the lack of consistent results from using foliar fungicides across trials and locations, foliar fungicides should not be used on corn unless disease resistance of the hybrid was susceptible.

References:

Esker, P., Halfman, B., and Jensen, B. 2009. Management decisions for foliar fungicides in corn. Proceedings of the 2009 Wisconsin Crop Management Conference, Vol. 48: 47-50.

Lauer, J. 2002. Methods for calculating corn yield. Agronomy Advice. Available on at http://corn.agronomy.wisc.edu/AA/A033.aspx

Shaner, G. 2008. Regional Corn Fungicide Trials – 2008. Presented at the 2008 Corn Disease Management Working Group Meeting, Chicago, IL.