Solving the fungicide puzzle

Jun 05, 2023

By Taylor Dill, Tennessee Agronomy
Manager, GreenPoint Ag
Successfully growing high-yielding corn in the warm and humid southeast U.S. is more of a challenge than many people realize. There is a minefield of decisions for a farmer to make, and choices can result in a loss of profits or just the opposite: higher yields and a better bottom line.

The variables are massive. Chief among these is the choice of seed hybrid. With corn, most yield potential is set before or at planting based on hybrid selection, seeding rate, total nitrogen budgeted, ground conditions at planting, and fertility (excluding, of course, rainfall in a dryland scenario). After the decisions are made, we then protect that yield from pests — weeds, insects, and disease. Those decisions aren’t always easy to make. If every dollar of input applied to a field of corn doesn’t result in a positive return of investment (ROI), the decision was not a sound one.

Fungicide applications are often made to produce high-yielding corn in our area of the country because several diseases either thrive here or, at the very least, have the potential to. These include anthracnose, leaf blight, common rust, eyespot, gray leaf spot, northern corn leaf blight, and southern rust — which can have the biggest impact if it reaches corn early enough.
First choice — hybrids
One of the earliest decisions a producer will make will be his choice of a corn hybrid. Co-op is uniquely set up to help growers with this through a combination of local on-farm trials though partnership with GreenPoint Ag in combination with Winfield’s Answer Plots to dial in management of nitrogen, fungicide, and seeding rate.
First, it helps to fully understand what response-to-fungicide (RTF) rankings mean. When a new corn hybrid is released to the market, Winfield United Technical Seed Agronomists and Answer Plot Crews evaluate them for their RTF. Multiple reps of those hybrids are sprayed with a fungicide alongside an identical untreated check (set of rows) of the exact same hybrids. Then, throughout the year, the crews conduct disease rankings — pre- and post-application — to get an idea of what the disease pressure is, which fungicide products are working best, and differences in the same hybrid that has been sprayed or left alone. At the conclusion of the season, that information is collected — along with yields — viewed holistically, and then segregated into low, medium, and high response to disease pressure.

A low-RTF hybrid means that the yield response was right at or below the break-even point when you consider the fungicide and application costs versus the commodity prices for that year.

A moderate-RTF hybrid is right at or above break-even for those same variables. Sometimes you will gain a little, sometimes you’ll be slightly under.

Then, a high-RTF hybrid is always well above the break-even point. Regardless of the disease environment, they will return a positive ROI.

All of these hybrids are good products that the producer should consider planting based on local performance, soil type, and management practices. When we talk about RTF, we’re only talking about the yield response to being sprayed with fungicide — not the overall yield.
Modes of action
So, how do you, the grower, use this information on your farm? First select a hybrid based on local performance and your desired management practices. When it comes time to apply fungicide, optimally at tassle (R1), consider yield potential, market prices, current conditions, and disease pressure. In 2022, because of the severe drought through West and parts of Middle Tennessee, not many corn fungicide applications were made because the yield potential was simply not there. However, these applications have increased over the last several years thanks to new, better fungicides that include multiple modes of action, and response has been more consistent along with yield, plant health, standability, and test weight benefits.

Multiple modes of action provide a broader range of control if fungicide resistance is present, and also delay that disease resistance. All corn fungicides include either Group 11 Qol Strobilurins, Group 3 DMI Triazoles, and Group 7 SDHI or some combination of the three. There are also more opportunities to apply fungicide to tassling corn. In the past, an area might be limited for a plane or helicopter, but several Co-ops across the state now offer custom drone applications — along with third party services — which gives growers more opportunity to protect their corn crop.
In case of southern rust
The biggest exception to this decision making is the presence of southern rust, a disease caused by the pathogen Puccinia polysora. Southern rust generally develops in the southernmost corn states and then moves north via prevailing winds if the conditions are favorable — which usually means high temperatures and humidity. If southern rust is present, regardless of RTF, corn will benefit from a fungicide application.
How do fungicides work?
While field crops can also be infected by bacterial and viral diseases, fungicides are only active on fungal diseases, which occur when fungal spores germinate and penetrate a plant. The fungus grows in, on, and through the plant, and may reproduce, releasing spores that can lead to secondary infections. For fungi to infect the crop, the fungi (pathogen), the host (crop), and a favorable environment must all be present at the same time, which is often the case in the Southeast.

There are two classifications of fungicides: contact and systemic, which can be preventative and curative.
Contact fungicides work on the leaf surface to prevent fungal spores from germinating or penetrating the plant. These products require the most care in application because complete coverage is essential for effectiveness. Systemic fungicides work inside the plant and can be locally systemic or moved throughout the plant. Systemic fungicides can be preventative and curative.

As suggested by their name, preventative fungicides prevent fungal infection to the plant. Curative fungicides, on the other hand, can enter the plant and stop fungal infection after it has occurred. Curative fungicides can help prevent spore infection from spreading and forming lesions to ultimately prevent re-infection. Fungicides cannot repair damaged tissue caused by fungal infection; therefore, fungicides should be used before serious infection has occurred.
Plan on using an adjuvant
When the time comes to spray fungicide, you should do everything you can to make that product pay, and that includes using a high-quality adjuvant. This holds true regardless of which fungicide you’re using, whether you’re using a ground rig, a helicopter, airplane, or drone. WinField® United MasterLock® does a great job of controlling drift and improving deposition — getting that product all the way down throughout the canopy and making it stick to the leaf surface. Winfield reports a 5.7 bushel advantage when adding MasterLock to the fungicide application. Masterlock is unique in that it is not a NPE adjuvant which can cause arrested ear.

Remember, as a Co-op member or customer, you have access to a great deal of experience and expertise in the agronomy professionals at your local store. Don’t hesitate to reach out and schedule a fungicide consultation.

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