Every crop season sets up different conditions for the development and progression of disease in corn and soybeans. Farmers and researchers have had a wide variety of results with foliar fungicide use over the years, from no response to huge yield increases, especially in corn – depending upon numerous variables.

Mike Meyer, plant pathologist and field development representative with DuPont Crop Protection, offers his expertise in assessing risk factors for disease when determining whether a fungicide application is likely to deliver a return on your investment.

1.      What does field history reveal?

Field history is important, especially when you have limited input dollars to spend on fungicide applications. “After you’ve eliminated all other yield-limiting agronomic factors, such as subpar soil fertility and poor drainage, and you have a history of disease or have planted a disease-susceptible hybrid or variety, then a fungicide application is most likely to provide a return on investment,” Meyer says.

2.      How are environmental conditions?

Most fungal diseases in corn and soybeans develop when conditions are wet or humid with moderate temperatures. Watch the extended forecast – if wet or humid conditions are expected to persist, a fungicide can help protect yield. Dry, hot temperatures naturally halt disease progression, and a fungicide application may not be as beneficial. Still, Meyer adds, “It is not uncommon to see yield increases in the absence of disease-favorable weather conditions due to the beneficial plant health effects associated with applications of strobilurin-containing fungicides.”

3.      How severe is the disease?

Because many variables affect disease development, it’s difficult to establish economic thresholds for most diseases in row crops. In corn, start scouting before tasseling and look for disease developing in the lower canopy. The earlier disease develops, the more likely it is to cause yield damage.

“The ear leaf and leaves above the ear contribute 75 to 90 percent of the carbohydrates to fill grain,” explains Meyer. “If disease is reducing green leaf area on these leaves or is quickly progressing up the plant, yield reduction is more likely to occur.”

In soybeans, scout fields prior to flowering to assess disease severity and loss of green leaf area. Foliar fungicides applied between late flowering and pod-filling stages can improve grain quality, test weight and yield.

Meyer says white mold in particular infects soybeans early in the season, but signs generally show up much later, when control won’t be effective. “It’s important to be proactive to prevent white mold. In areas with heavy soybean white mold pressure, an R1 fungicide application, with a repeat application 14 days later, is critical to protecting the soybean plant during the primary infection period. DuPont Aproach fungicide is especially effective on white mold.” He says university trials on soybean white mold control have shown an average increased revenue of $169 per acre when Aproach was applied at the R1 and R3 growth stages, compared to an untreated control, based on soybeans at $10.61 per bushel.

4.      Will your seed hold up to disease?

Purchasing seed hybrids and varieties that are resistant to fungal diseases is a good way to protect yield potential. Meyer says it’s important to plan seed placement according to individual field conditions, making sure vulnerable fields have the right defensive traits and disease packages to meet yield goals. In general, fungicides deliver a greater return on investment on varieties that are more susceptible to fungal disease.

5.      When do you expect to harvest?

Fungicides can help protect stalk integrity, which is especially critical for late-harvested corn. Plants that are stressed by foliar disease convert less light into sugar for grain fill. They compensate by pulling carbohydrate reserves from the stalk, resulting in poor standability late in the season. If you need to plan for a late harvest due to field conditions or workload, it may pay to apply a fungicide for more efficient harvesting and less grain loss. Meyer recommends DuPont Aproach Prima fungicide with two modes of action to protect plant health for increased grain quality and yield potential in corn, soybeans and wheat.

“Multi-year trial data has shown an average 17-bushel-per acre yield advantage on hybrids that were treated from VT to R3 with Aproach Prima compared to an untreated control. One benefit of this product is that it protects the inside and outside of the plant and re-distributes throughout the canopy for better coverage.”

Find scouting tips and disease-control strategies at fungicidevalue.dupont.com.

Other resources:

A Farmer’s Guide to Corn Diseases: http://crops.extension.iastate.edu/node/1870

A Farmer’s Guide to Soybean Diseases:

http://crops.extension.iastate.edu/farmers-guide-soybean-diseases

Corn and soybean scouting calendar:

https://www.pioneer.com/home/site/us/agronomy/crop-management/scouting/