High management corn systems have gained popularity in recent years and V-5 fungicide application is one of the components commonly used in those systems. Typically, the fungicide is tank mixed with the post herbicide application and the second application of fungicide is applied at the VT/R1 growth stage. The purpose of this article is to focus on the capabilities and limitations of applying a fungicide at the V-5 growth stage.
Disease Control
V-5 fungicide applications are effective in reducing disease incidence and severity for diseases that overwinter in crop residue. Grey Leaf Spot, Anthracnose Leaf Blight, and Northern Corn Leaf Blight are examples. One exception to this is Tar Spot. Although Tar Spot overwinters in crop residue, V-5 applications have not been effective in controlling Tar Spot since it is prone to cause infection later in the season. The most consistent application timings for severe infections of Tar Spot in the Northern Corn Belt have been VT followed by R3. The V-5 fungicide applications are not likely to control of diseases like Southern Rust that do not overwinter in residue since spores are deposited and infect later in the growing season. V-5 fungicide applications will not be effective on diseases like Southern Rust do not overwinter and rely on weather fronts to deposit spores from the South. The VT/R1 timing has provided the most consistent control of Southern Rust. Some factors that increase the likelihood and severity of disease pressure include, corn on corn, no-till, minimum-till, and susceptible hybrids.
Fungicide Mobility
Mobility of fungicides in the plant can vary widely and the products we use in row crops are not fully systemic like systemic herbicides. Fungicide mobility can be grouped into 4 basic categories:
- Contact – older products that are not absorbed in the leaf and can be washed off with rain. Examples are copper, mancozeb, chlorothalonil.
- Translaminar – fungicide applied to the upper leaf surface moves through the leaf to the lower leaf surface. Limited mobility.
- Xylem Mobile – also known as acropetal, mobile within the water conducting tissue of the plant. Xylem mobile fungicides move outward towards the leaf tip on leaves at the time of application and do not move into new leaves that emerge after the application. A xylem mobile fungicide applied at V-5, will not be present in the upper leaves at the V-8 growth stage.
- Xylem and Phloem Mobile – also known as amphimobile, which is fully systemic. Currently there are no products used in row crops that fall in this category.
Fungicide FRAC (Fungicide Resistance Action Committee) Groups – there are 3 main groups of fungicides labeled for corn and there are premixes that have one from each group.
- FRAC Group 3. DMI’s – Di-Methylation Inhibitors also known as triazoles. DMI’s are xylem mobile and generally short residual activity, 7-14 days.
- FRAC Group 11. QoI’s – Quinone Outside Inhibitors also known as strobilurins. QoI’s range in mobility from translaminar to xylem mobile. Long residual activity 21+ days.
- FRAC Group 7. SDHI’s – Succinate-Dehydrogenase Inhibitors. Xylem mobile and long residual activity 21+ days.
For information on fungicide efficacy ratings, here is a link to the Crop Protection Network. https://cropprotectionnetwork.org/publications/fungicide-efficacy-for-control-of-corn-diseases This link provides control ratings for fungicide products as well as a breakdown of active ingredients and FRAC Groups for each product.
Although V-5 fungicide applications have some limitations on disease control, they have provided additional yield and ROI by controlling early season diseases. Talk to your Crop Specialist about the best products and timing for your operation.
Anthracnose Leaf Blight. Photo Credit: Alison Robertson, Iowa State University.
Grey Leaf Spot
Southern Rust
Tar Spot
Related categories: diseases, fungicides, application timing