Which fungicide timing will deliver the best return on investment? How do I pick fungicides? How much carrier do I need?

The Indiana certified crop adviser panel answering this question includes Betsy Bower, agronomist for Ceres Solutions, Terre Haute; Abby Horlacher, Nickel Plate Consulting, Frankfort; Brian Mitchem, proprietary products manager for Nutrien Ag Solutions, Fort Wayne; and Dan Quinn, Purdue Extension corn specialist, West Lafayette.

Bower: It depends on the season and what diseases are in the canopy at VT through R2. Last year was dry in June in southwest Indiana. We did not see any disease until we received 1- to 2-inch rains in mid-to late July. In 2022, those who waited until brown silk were probably not hurt much. But in 2021, due to a wet June, in fields with tar spot or gray leaf spot, R2 or brown silk was likely too late. Some diseases already had a foothold.

For 2023, keep track of rainfall from V8 to tassel, and start scouting for diseases at V8 to V9. If you find lesions and are unsure what they are, get with your trusted adviser. The Purdue Plant and Pest Diagnostic Lab is a great resource to help quickly identify lesions for a very low cost.

Late-planted fields will likely always be best protected at VT. They pollinate later, when we tend to see more disease pressure.

Horlacher: Timing of fungicide depends on how it’s applied and disease pressure. If fungicide goes on with a helicopter, you do not have much say on when it is applied. With a ground rig, you have a little more control. If you are low on disease, hold off till after VT to get the best coverage. If you can use a ground rig, the more carrier, the better to increase coverage on the plant. 

Mitchem: Fungicide applications have proven most consistent when applied close to the reproductive stage. I prefer slightly earlier as opposed to later, especially with more aggressive foliar diseases like tar spot and southern rust. Otherwise, you may not get equipment when you need it.

I believe most fungicides will provide similar performance when compared in nonbiased settings. There are exceptions, however, particularly with southern rust. Specific products have better performance. Use the Purdue fungicide effectiveness chart for specific performance information.

Cover as much of the ear leaf as possible. It’s difficult to drive a lot of material into the canopy. Deposition aid adjuvants help. Water volume plays a role: 15 gallons by ground and 2 gallons by air are minimums. If applying with a pivot, the lowest amount of water possible is advised.

Quinn: Typically, the most consistent timing to apply corn fungicide is the VT/R1 growth stage. This timing provides the most consistent disease control and yield response, year in and year out. However, fungicide applications at R2, and in some cases, even R3, can still perform well. It often does not pay to apply a fungicide at the R4 growth stage and beyond.

If disease symptoms are observed earlier, closer to pollination, it would be worth spraying at VT/R1. However, if not much disease is present at VT/R1, continue scouting and spraying at R2 or R3, if you find disease symptoms later. To find the best fungicide, use the fungicide efficacy chart from the Crop Protection Network. You will find other resources on disease there as well.