Do we or Don’t We? Corn Fungicides

We’re in the middle of a challenging growing season with significant crop stress in many areas of the Mid-Atlantic region. Entering the tasseling and grain fill stages raises many questions.

 

• Should I put fungicides on my crop this season?

• Do fungicides help under drought conditions?

• How much disease pressure is there?

• Which diseases are likely to be most problematic this season?

• Some people tell me to apply fungicides, and some tell me not to; who’s right?

 

Let’s think through some of these questions.

 

 

Do fungicides help under biotic or abiotic stress?

Heat and drought are abiotic stresses, while diseases or nutrient deficiencies are examples of biotic stresses. We know that fungicides protect against selective pathogens that can infect the plant. Different chemistries or modes of action give different levels of control against various disease organisms, helping the plant defend itself against yield-robbing infections. Some fungicides that contain strobilurin chemistry can assist with stress mitigation from abiotic stress. Ethylene is a hydrocarbon gas and a naturally occurring plant hormone. Strobilurin chemistries can regulate ethylene production within the plant, allowing the plant to better handle abiotic stresses by affecting plant growth, respiration, and water use efficiency.

 

What potential diseases could be problematic this season?

Penn State positively identified Tar Spot on July 10. It is already present in fields in multiple counties across Pennsylvania. This infection date is considerably earlier than any of the past three seasons. Early on, we believed Tar Spot would be most viable and problematic when temperatures were milder, as in the following statement: Cool temperatures (60°–70° F), humid conditions (>75% relative humidity), and at least 7 hours of leaf wetness due to rain, fog, dew, or overhead irrigation favor Tar Spot infection and development. We need to rethink this based on the heat and drought stress we have experienced this growing season and the fact that we already have infections. Tar Spot is a critical disease to prevent because once it sets in, it is not curative with fungicides, and heavy infections can be a significant yield robber. We can also expect Grey Leaf Spot to be challenging when heat and humidity are present.

 

Application timing…

Typically, we lean towards early applications to prevent disease infections. The application window is large and can range from initial tassel emergence through brown silk. With today’s fungicide portfolio, we have longer-lasting technology that can protect for more than 30 days, so applications applied at silking will keep you protected through the grain fill stages of growth.

 

Some people tell me to apply fungicides, and some tell me not to. Who’s right?

They both are! Realistically, severe drought stress may limit the crop beyond the point of getting a reasonable response or return on investment with a fungicide. Though strobilurin fungicides can help manage abiotic stress, they do not override the need for adequate rainfall to build yield.

 

Let’s be objective, identify the fields that have the greatest yield potential, and protect them. Some later-planted corn may be more at risk as the disease pressure builds throughout the season.

 

The weather has been very spotty across the Mid-Atlantic region, and we need to ask all the right questions as we consider our options to protect the crop and maximize yields for the rest of the season. We are always eager to assist you in any way we can to optimize your crop management efforts.