Four tips for managing crop disease

Pulling back on disease management can be tempting when commodity prices fall. While lower input costs may sound like an easy way to save money, the risk of diseases decimating corn yields increases significantly.

“Economics, at the end of the day, is going to drive a lot of the decisions,” says Ryan Bryant, a herbicides technical development manager for UPL. “When considering inputs, we have to keep that return on investment in mind but also understand what the risk is if we don’t make any applications.”

Understand disease risk

Disease pressure can vary greatly from year to year and field to field. Stay informed on which diseases could emerge. Gray leaf spot, Northern Corn Leaf Blight, and Diplodia leaf streak remain prevalent throughout most of the Corn Belt, while tar spot and Southern rust also are increasing concerns.

“Southern rust doesn’t overwinter in the U.S.; it blows in from South and Central America, so the conditions there determine how much rust and spores get up here,” says Tyler Harp, technical fungicide manager for Syngenta Crop Protection. “In a bad year, it can be very devastating,” he says. “Tar spot does overwinter here, so if growers have had tar spot diagnosed in their [counties], they’re always going to have to be on the lookout for that.”

Weather significantly affects corn disease spread. In 2023, dry conditions meant extremely low disease pressure in many parts of the Corn Belt, but that’s no reason to relax this season, with its early abundant rain.

Disease can be most severe when farmers don’t pay attention, Bryant says. “When we start to see those conditions develop, hopefully, that means we’re getting some rain,” he notes. “We just need to be mindful of the conditions and what is associated with each disease.”

Scout early and often

Getting into fields early and tracking any disease progression can allow for timely decisions regarding fungicide applications. To catch early symptomatology, Bryant recommends thorough scouting during the early reproductive stages.

In some cases, scouting when weather points to higher disease risk can save fields from devastating yield losses. Tar spot, for example, can explode in cooler, humid conditions, when leaves are exposed to wetness for an extended period.

“When we start to see the stars align for that type of situation, that’s when we really need to be on our game and get a timely fungicide application made before we see significant incidence of disease,” Bryant says.

When scouting, be sure to evaluate the entire plant, since different diseases may appear on different parts. Also, root digs can show evidence of hidden diseases such as crown rot.

Understand fungicide value

Fine-tuning input applications can help with cost cutting, but don’t lose sight of fungicide benefits.

“Our goal, especially in a year like this, with commodity prices lower, is to educate people about the importance of knowing what’s in their program and what value it’s bringing to their farm,” says Camille Lambert, a technical service manager for FMC.

Strong, overlapping residual herbicide programs and a foliar fungicide can help ensure every bushel is protected, Lambert says.

Beyond disease control, some fungicides offer plant health benefits such as stress mitigation.

Today’s fungicides aren’t like those your father or grandfather used, Syngenta’s Harp says. For example, he points out, Syngenta’s new plant-health fungicides contain a newer carboxamide and SDHI chemistry, which can mitigate stress.

“We’re not only preserving yield in the presence of biotics such as diseases,” he says, “but we’re preserving yield in the presence of abiotic stress such as heat and drought. There’s a whole new value in what these products can deliver in terms of yield preservation.”

Harp says data from 550 field trials across the Corn Belt showed a profitable return on investment 80% of the time when using Syngenta’s biofungicide.

For some farmers, those added benefits may mean applying fungicide becomes less situational and more part of routine agronomic practice. Applying fungicide preemptively, when timed right, also could lead to better disease control.

Once you have some disease or stress, an applied fungicide can protect from subsequent stress or disease but won’t repair existing damage. “It’s best to protect your investment with a preventative application,” Harp recommends.

Manage resistance

Once, farmers often relied heavily on one active ingredient rather than pair it with other control methods. But to extend the life of existing control options, make resistance top of mind.

“When you put all the selection pressure on one active ingredient, that generates pathogen resistance,” Harp says. “Today we use two-and three-way mixtures, where each active ingredient is effective on the given pathogen. The selection pressure is spread among two or three different powerful modes of action, which helps us to minimize resistance.”

Using robust rates, rotating active ingredients when making additional applications, and incorporating novel modes of action can also limit disease resistance.