When to Pull the Fungicide Trigger

When to Pull the Fungicide Trigger

Spraying is expensive, but are you losing money by sacrificing yield?

Now’s the time to stop what you’re doing and check the health of your crops. Margins are tight, but you don’t want to get to harvest and realize you could have prevented issues such as down corn. 

Fungus and disease infestations commonly infect the plant during reproduction—pollination or flowering. If leaf tissue is affected, it will decrease photosynthesis—resulting in lower test weights, less flowering and, ultimately, lower yields.

“Fungicide doesn’t magically increase yield. It saves yield potential,” says Travis Miller, corn specialist with AgriGold.

Timely fungicide application has the potential to save 4 bu. to 15 bu. per acre, according to Iowa State University research.

During reproductive stages, plants need to focus all of their energy on photosynthesis and grain fill. Don’t let stress from fungus or disease detract from it, says Andrew Ferrel, Mycogen Seeds commercial agronomist.

“The problem with corn pollination is it only happens once,” Ferrel adds.

Gaining control of possible disease and fungus infestation starts before reproductive stages. It begins at seed selection, says Chris Doud, Pioneer field agronomist.

“If you historically have incidents of foliar diseases, it’s important to check your hybrid package for tolerance to diseases common to your environment,” he notes. 

Keep track of where you have seen fungus and disease pressures. Many fungi and diseases overwinter in cornstalks or other organic trash. For example, sudden death syndrome overwinters in soybeans and northern corn leaf blight in corn, which means they can affect crops in years to come. In these fields, it’s important for crop genetics to be the first line of defense.

In some cases, genetics are not enough. When an infestation strikes, it’s key to know what to look for when considering a fungicide application.

“Intensify scouting at key fungicide spraying times,” Miller says. “Then we can see if it will increase profit.”

Increase scouting one to two weeks prior to tassel in corn and just prior to reproduction or in early reproductive stages in soybeans. After tassel in corn and R5 in soybeans, there is less chance for prevention, and a fungicide application would likely be too late or at best a rescue treatment. 

As a general rule of thumb, consider a fungicide application if a fungal disease is present on the third leaf below the ear leaf or higher on 50% of the plants at tasseling—which is when plants are susceptible to disease, according to Iowa State University. 

Recommendations vary, though, so talk to a local company representative or Extension agent to check thresholds. Be prepared to act quickly if needed.

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