Pioneer Fungicide Research
Pioneer scientists, agronomists, and university collaborators have conducted several corn fungicide studies in which a single foliar disease was predominant at the research location or locations. In some cases, research locations were chosen specifically due to their history of a specific disease; in others, environmental conditions happened to be favorable for a given disease when the study was conducted.
Gray Leaf Spot
A research project was conducted over three years at the University of Tennessee Research and Education Center at Milan at a research site specifically chosen due to a history of high gray leaf spot pressure. The primary goal of this study was to determine the yield benefit associated with foliar fungicide management of gray leaf spot in hybrids with differing levels of genetic resistance. The plot area was in irrigated no-till corn production for four years prior to the start of the study, with a high level of gray leaf spot each year. Three Pioneer brand corn hybrids with differing levels of resistance to gray leaf spot were included in the study.
Results of the study demonstrated the potential for gray leaf spot to cause substantial reductions in yield when disease pressure is very high. Hybrid resistance was effective in mitigating a large portion of yield loss due to gray leaf spot; however, even with the most resistant hybrid, the yield benefit of the foliar fungicide application was great enough to potentially cover the cost of product and application (Figure 2). Under more moderate disease pressure, a fungicide application would likely not provide an economic benefit on a resistant hybrid.
Figure 2. Average yield response of hybrids susceptible, moderately resistant, and resistant to gray leaf spot to foliar fungicide application in a 3-year Univ. of Tennessee/ Pioneer research study.
Pioneer scientists conducted fungicide research trials at several Midwestern sites in 2009, a growing season that experienced unusually high common rust pressure in parts of the Midwest. Summer temperatures were cooler than normal in 2009, which favors development and spread of common rust. Studies were conducted at ten different field locations across five states. Corn yield response to fungicide application varied widely among research locations, largely due to differences in common rust pressure. Common rust was prevalent at research locations in Iowa, Illinois, and Indiana.
Table 2. Average corn yield response to foliar fungicide treatment at Pioneer small-plot research locations.
Average yield response across locations in Iowa, Illinois, and Indiana was 11.4 bu/acre (Table 2). Conversely, average yield response across Minnesota and Wisconsin locations where common rust was less prevalent was only 3.9 bu/acre. At sites with high common rust pressure, yield response to foliar fungicide application was greatest among hybrids with lower levels of genetic resistance to the disease (Figure 3).
Figure 3. Average fungicide yield response of hybrids with low resistance (3 on a 1-9 scale) and moderate resistance (4-6) to common rust in Pioneer small-plot trials.
Common rust was prevalent at a trial at Macomb, IL, along with low to moderate levels of gray leaf spot and northern leaf blight. Notable differences in disease symptoms and yield response to fungicide were observed (Figure 4).
Figure 4. Two hybrids treated (left) and non-treated (right) with fungicide at Macomb, IL. The fungicide helped to protect yield of a susceptible hybrid (top) but provided little benefit on a moderately resistant hybrid (above).
These research results from 2009 demonstrate the value of foliar fungicides in protecting yield when disease outbreaks occur; however, genetic resistance of hybrids may also provide adequate protection and should be considered in fungicide treatment decisions.
Northern Corn Leaf Blight
Pioneer on-farm trials were conducted at 40 locations in Iowa in 2015 to evaluate corn yield response to foliar fungicides applied at different timings. Northern corn leaf blight pressure was high in much of Iowa in 2015 and it was the predominant foliar disease at the trial locations (Figure 5). Trials compared yield of corn treated with DuPont™ Aproach® Prima fungicide at the VT, R1, or R2 growth stage to non-treated corn.
Figure 5. Field trial comparing fungicide treated (left) and non-treated corn (right) at a location with high northern corn leaf blight pressure in 2015.
Results showed that yield response to fungicide application varied by hybrid genetic resistance to northern corn leaf blight. A yield response of 13 bu/acre was observed with hybrids rated a 3 on a 1-9 scale for northern corn leaf blight, while hybrids rated a 6 for northern corn leaf blight had an average yield response of 9 bu/acre (Figure 6). Fungicide yield response was greatest at the VT application timing (Figure 7).
Figure 6. Average fungicide yield response of Pioneer® brand hybrids with different levels of genetic resistance to northern corn leaf blight in 40 Pioneer Agronomy trials in Iowa in 2015.
Figure 7. Average yield response to fungicide applications at the VT, R1, or R2 growth stages in 40 Pioneer Agronomy trials in Iowa in 2015.
Pioneer conducted fungicide research trials over two years in the southeastern U.S. at locations where southern rust was the predominant foliar disease.
A replicated research study was conducted near Camilla, GA in 2014 to assess southern rust infestation and corn yield response of six different Pioneer® hybrids with and without foliar fungicide treatment. This study included two different fungicide treatments: a single application at the V8-V10 growth stage, as well as a two-pass program with applications at both the V8-V10 stage and the VT-R1 stage. (The original protocol called for only the VT-R1 application, but treatment timings were altered when southern rust was detected earlier than expected at the research site.) Averaged over hybrids, there was no yield increase with early fungicide application alone, but yields were increased by an average of 20 bu/acre when the VT-R1 application was included (Figure 8).
Figure 8. Corn yield as affected by fungicide treatments near Camilla, GA in 2014.
(Means followed by the same letter are not significantly different based on Tukey’s HSD test conducted at the alpha=0.05 level. Means averaged over 2 planting dates and 6 hybrids.)
A study was conducted the following year across seven locations in five southeastern states to evaluate corn yield response to a single-pass fungicide application at VT-R1 for control of southern rust. Averaged over four hybrids and seven locations, corn treated with fungicide at the VT-R1 stage yielded 11 bu/acre more than non-treated corn (Figure 9).
Figure 9. Average yield of corn treated with Aproach Prima fungicide at the VT-R1 corn growth stage and non-treated corn across 7 southern research locations in 2015.
Figure 10. Corn treated with fungicide at VT-R1 compared to non-treated corn at a research location near Winchester, AR in 2015. Southern rust pressure was low at the time of application but increased in severity and ultimately caused premature death in the non-treated check before the end of the season.