The plots compared three fungicide application treatments with a check of no fungicide. The treatments included one at V5 (five-collar), one at R1 (silking) and one with applications at both growth stages.
Farm Journal Test Plot demonstrates how the disease triangle impacts the effectiveness of fungicide application timings.
As producers become more proactive than reactive to disease management, the fundamentals of the disease triangle become increasingly important. The three sides of the disease triangle—a conducive environment, a present pathogen and a susceptible host—drive the decision of when (or even whether) to spray fungicides.
"Farmers ask if they could shift their application timing to V5 or split applications to V5 and R1," says Missy Bauer, Farm Journal Associate Field Agronomist. "But it really depends on the disease triangle. All three of these elements must be aligned to have disease present, and there must be some kind of disease pressure for a fungicide to be able to protect or increase yields."
Bauer recently concluded a three-year Farm Journal study examining the impact the disease triangle has on the effectiveness of fungicide and various application timings. The first year of the study included irrigated corn on corn and corn following soybeans, but the final two years focused exclusively on irrigated corn on corn, the environment ripe for higher disease pressure and in turn, a higher response to fungicide application. That’s because the disease inoculum can overwinter on old corn residue—and the steady availability of water is more likely to roll out a welcome mat for disease.
"Every year, we ran replicated, randomized trials to evaluate the hybrids’ response to fungicide and the timing of application," Bauer explains. "Each year, we used two hybrids—one that is identified by disease ratings as being more susceptible to disease and one with more resistance."
Three application timings at various growth stages were included in the trial: only V5, (five-collar), only R1 (silking) and both V5 and R1. Each was compared with a check of no fungicide. A high-clearance, self-propelled sprayer delivered all applications.
The wettest and most humid of the three years, 2010, provided the opportunity for the strongest response to fungicide use. When the two hybrids were averaged, compared with the check, the application at V5 was 6.2 bu. more; the application at R1 was 9.3 bu. more; and the two timings combined yielded 11.1 bu. more.
All Farm Journal Test Plots are harvested with calibrated yield monitors, and each bushel is weighed by grain carts outfitted with scales.
"This year  emphasized how important the disease triangle is to fungicide results. We saw early season anthracnose pressure, late-season heavy pressure of northern corn leaf blight and gray leaf spot," Bauer says.
The following year, 2011, brought overall moderate disease pressure. When the yields were averaged for the hybrids, compared with the check, the application at V5 was 1.3 bu. more; the application at R1 was 8.8 bu. more; and the two together were 6.9 bu. more.
In the drought of 2012, Bauer continued the study despite lower disease pressures. When both hybrids were averaged compared with the check, the application at V5 was 1.5 bu. more; the application at R1 showed no response; and the two timings were 1.8 bu. more.
"The hot, dry conditions with low humidity provided a poor environment for disease," Bauer explains.
Overall, the three test years with three wide-ranging in-season environments emphasized the importance of paying attention to the disease triangle when making fungicide decisions.
"You can’t adjust any crop management practice without paying attention to the agronomics behind the decisions," she adds.
Built-in defense. Hybrid selection also played a key role in the plot yields. That’s because one hybrid had a stronger response to the application based on the characteristics of the host.
- September 2013