Effect of Plant Population on Corn Yield Response to Fungicides

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Objectives

Over the past 2 years, Pioneer field agronomists have conducted a series of studies to evaluate the value of foliar fungicides in corn planted at higher populations.
The theory was that denser canopies at high populations would tend to be more prone to foliar disease due to reduced light and air movement through the canopy, which could results in stalk lodging and yield loss.

Study Description

Locations:	60 Iowa on-farm locations over 2 years
Hybrids:	Results are pooled across 47 hybrids.
Populations: (plants/acre)	• 30,000 • 38,000 • 34,000 • 42,000
Treatments:	Untreated, Treated

• Fungicide strips were applied perpendicular to hybrid and plant population strips at each
location. Treatment widths varied but were a minimum of 250 ft.

Results

Weather patterns for the years of this study ranged from extreme to moderate drought over most of the study area (Figures 1 & 2).
Averaged across locations, the yield response to fungicide treatment was greater in corn following corn compared to corn following soybeans (Figure 3).
In higher yielding fields, yield response to fungicide treatment was greater at higher plant populations (Figure 4).
In lower yielding fields, corn yields were typically greater with fungicide treatment but yield response did not differ as greatly across populations (Figures 5 & 6).

Figures 1 & 2. Seasonal rainfall was below historical norms for the time period of this study. Top: 2012, Bottom: 2013.

2013_rainfall — Source: Midwest Regional Climate Center

Figure 3. Yield advantage for fungicide was greater in corn following corn compared to corn following soybeans. (n=60 Iowa locations over 2 years)

Figure 4. Corn yield response to population and fungicide treatment in environments yielding greater than 200 bu/acre. n=21 locations, 2 years and 39 hybrids.

Figure 5. Corn yield response to population and fungicide treatment in environments yielding less than 150 bu/acre. n=9 environments, 2 years and 23 hybrids.

Figure 6. Corn yield response to population and fungicide treatment in environments yielding between 150 and 200 bu/acre. n=30 environments, 2 years and 43 hybrids.

Conclusions

Results of these studies tend to support the hypothesis that foliar fungicides would provide a greater yield benefit at greater plant populations in high-yield environments.
However, previous crop was a more important factor affecting yield response to foliar fungicide treatment.
Corn diseases pressure during the years of this study was modest to light. Fungicide would be expected to have a greater value in years with significant disease pressure.